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S > 221hh > Where: L= Length of vertical curve (ft) S= Sight distance (ft) A= Algebraic difference in grades (%) > h1= Eye height (3.50 ft) > h2= Object height— see text (ft) Sight Distance, Crest Vertical Curve > Figure 650-4 When SL ASL > 221 200 2 hh A 100 2LS2 > 21 hh > When S 2212200 hh > AS L > A200L S > 221hh > Where: L= Length of vertical curve (ft) S= Sight distance (ft) A= Algebraic difference in grades (%) > h1= Eye height (3.50 ft) > h2= Object height— see text (ft) Sight Distance, Crest Vertical Curve > Figure 650-4 > When S>L ASL > 221 200 2 hh A 100 2LS2 > 21 hh > When S 2212200 hh > AS L > A200L S > 221hh > Where: L= Length of vertical curve (ft) S= Sight distance (ft) A= Algebraic difference in grades (%) > h1= Eye height (3.50 ft) > h2= Object height— see text (ft) Sight Distance, Crest Vertical Curve > Figure 650-4 Where: L = Length of vertical curve (ft) S = Sight distance (ft) A = Algebraic difference in grades (%) h 1 = Eye height (3.50 ft) h 2 = Object height— see text (ft) Sight Distance, Crest Vertical Curve Figure 650-4 (4) Sag Vertical Curves Sag vertical curves are only a sight restriction during the hours of darkness. Headlight sight distance is used for the sight distance design criteria at sag vertical curves. In some cases, a lesser length may be allowed. (See Chapter 630 for guidance and requirements.) Use Figure 650-1 2 or the equations in Figure 650-5 to find the minimum length for a sag vertical curve to provide the headlight stopping sight distance when given the algebraic
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difference in grades. The sight distance greater than the length of curve equation is not used in Figure 650-1 2. When the sight distance is greater than the length of curve and the length of curve is critical, the S>L equation given in Figure 650-5 may be used to find the minimum length of curve. When a new sag vertical curve is built or an existing one is rebuilt with grades less than 3%, provide Design Stopping Sight Distance from Figure 650-1. When grades are 3% or greater, see 650.04(2) for required sight distance. When evaluating an existing roadway, see 650.04(7) .Sight Distance Design Manual M 21-01 Page 650-4 May 2006 Where S>L > Figure 650-4 > Where S>L A3.5S 400 ‑2S L > 3.5 2A 400 LA S > Where S 5.3400 2A 1600AL 3.5L 3.5L S2r > Where: L= Curve length (ft) A= Algebraic grade difference (%) S= Sight distance (ft) Sight Distance, Sag Vertical Curve > Figure 650-5 > Figure 650-4 > Where S>L A3.5S 400 ‑2S L > 3.5 2A 400 LA > S > Where S 5.3400 2A 1600AL 3.5L 3.5L S2r > Where: L= Curve length (ft) A= Algebraic grade difference (%) S= Sight distance (ft) Sight Distance, Sag Vertical Curve > Figure 650-5 Where S Figure 650-4 > Where S>L A3.5S 400 ‑2S L > 3.5 2A 400 LA S > Where S 5.3400 2A 1600AL 3.5L 3.5L S2r > Where: L= Curve length (ft) A= Algebraic grade difference (%) S= Sight distance (ft) Sight Distance, Sag Vertical Curve > Figure 650-5 > Figure 650-4 > Where S>L A3.5S 400 ‑2S L > 3.5 2A 400 LA S > Where S 5.3400 2A 1600AL 3.5L 3.5L S2r > Where: L= Curve length (ft) A= Algebraic grade difference (%) S= Sight distance (ft) Sight
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Distance, Sag Vertical Curve > Figure 650-5 Where: L = Curve length (ft) A = Algebraic grade difference (%) S = Sight distance (ft) Sight Distance, Sag Vertical Curve Figure 650-5 (5) Horizontal Curves Use Figure 650-13 a or the equation in Figure 650-7 to check for adequate stopping sight distance where sight obstructions are on the inside of a curve. A stopping sight distance obstruction is any roadside object within the M distance (such as median barrier, guardrail, bridges, walls, cut slopes, wooded areas, and buildings), 2 feet or greater above the roadway surface at the centerline of the lane on the inside of the curve. Figure 650-13 a and the equation in Figure 650-7 are for use when the length of curve is greater than the sight distance and the sight restriction is more than half the sight distance from the end of the curve. When the length of curve is less than the stopping sight distance or the sight restriction is near either end of the curve, the desired sight distance may be available with a lesser M distance. (See Figure 650-6.) When this occurs, the sight distance can be checked graphically. MPT PC Objects within this area might be sight obstructions. L of lane on the inside of the curve C Sight Distance Area on Horizontal Curves > 650-6 Sight Distance Area on Horizontal Curves Figure 650-6 When the road grade is less than 3%, provide Design Stopping Sight Distance from Figure 650-1. When the grade is 3% or greater, see 650.04(2) for required sight distance. In urban design areas, with justification, a 2.00-foot object height ( h2) may be used. When h2=2.00 feet, roadside objects between 2.00 feet and 2.75 feet might not be a sight obstruction. (See Figure 650-13b for guidance on determining whether
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a roadside object is a sight obstruction.) When evaluating an existing roadway, see 650.04(7) . > »¼º«¬ª¸¹·¨©§RS28.65 cos RM1 »¼º«¬ª ¸¹·¨©§ RMRcos 28.65 RS 1‑ Sight Distance, Horizontal Curves > Figure 650-7 > »¼º«¬ª¸¹·¨©§RS28.65 cos RM1 »¼º«¬ª ¸¹·¨©§ RMRcos 28.65 RS 1‑ Sight Distance, Horizontal Curves > Figure 650-7 Where: M = Distance from the centerline of the inside lane of the curve to the sight obstruction (ft) R = Radius of the curve (ft) S = Sight distance (ft) Sight Distance, Horizontal Curves Figure 650-7 Design Manual M 21-01 Sight Distance May 2006 Page 650-5 (6) Overlapping Horizontal and Vertical Curves A vertical curve will affect the height at which a roadside object will become a sight obstruction. A crest vertical curve will raise roadside objects and make them more likely to become sight obstructions. A sag vertical curve will lower roadside objects, making them less likely to be sight obstructions. (7) Existing Stopping Sight Distance Existing stopping sight distance is used when the vertical and horizontal alignments are unchanged, the sight obstruction is existing, and there are no problems related to the sight distance. Figure 650-8 gives the values for existing stopping sight distance and the associated K C and K S. When evaluating the existing sight distance, use an object height ( h2) of 2.00 feet. For crest vertical curves where the existing vertical alignment is retained and the existing roadway pavement is not reconstructed, existing stopping sight distance values in Figure 650-8 may be used. The minimum length of an existing crest vertical curve may be found using the equations in Figure 650-4 and h2=2.00 feet, or using the K C values from Figure 650-8 . For sag vertical curves where the existing vertical alignment is retained and the existing roadway pavement is not
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being reconstructed, existing stopping sight distance values in Figure 650-8 may be used. The minimum length of an existing sag vertical curve may be found using the equations in Figure 650-5, or using the K S values from Figure 650-8. In some cases, when continuous illumination is provided, a lesser length may be allowed. (See Chapter 630 for guidance.) For horizontal curves, existing stopping sight distance values from Figure 650-8 may be used when all of the following are met at the curve: • The vertical and horizontal alignments are existing • The roadway pavement will not be reconstructed • The roadway will not be widened • The sight obstruction is existing • Roadside improvements to sight distance do not require additional right of way` A sight obstruction is any roadside object within the M distance from the equation in Figure 650-7 with a height more than 2.75 feet above the centerline of the inside lane. Roadside objects between 2.00 feet and 2.75 feet might be a sight obstruction. (See Figure 650-13b for guidance on determining whether a roadside object is a sight obstruction.) > Design Speed (mph) Existing Stopping Sight Distance (ft) KCKS > 20 115 616 25 145 10 23 30 180 15 31 35 220 22 41 40 260 31 52 45 305 43 63 50 350 57 75 55 400 74 89 60 455 96 104 65 495 114 115 70 540 135 127 75 585 159 140 80 630 184 152 Existing Stopping Sight Distance > Figure 650-8 Sight Distance Design Manual M 21-01 Page 650-6 May 2006 ## 650.05 Passing Sight Distance (1) Design Criteria Passing sight distance is the sum of four distances: • The distance traveled by the passing vehicle during perception and reaction time and initial acceleration to the point of
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encroachment on the opposing lane. • The distance the passing vehicle travels in the opposing lane. • The distance that an opposing vehicle travels during two-thirds of the time the passing vehicle is in the opposing lane. • A clearance distance between the passing vehicle and the opposing vehicle at the end of the passing maneuver. Sight distance for passing is calculated for a passenger car using an eye height ( h1) of 3.50 feet and an object height ( h2) of 3.50 feet. Figure 650-9 gives the passing sight distances for various design speeds. > Design Speed (mph) Passing Sight Distance (ft) > 20 710 25 900 30 1090 35 1280 40 1470 45 1625 50 1835 55 1985 60 2135 65 2285 70 2480 75 2580 80 2680 Passing Sight Distance > Figure 650-9 On two-lane two-way highways, provide passing opportunities to meet traffic volume demands. This can be accomplished by using numerous sections with safe passing sight distance or by adding passing lanes at critical locations. (See Chapter 1010.) In the design stage, passing sight distance can be provided by adjusting the alignment either vertically or horizontally to increase passing opportunities. These considerations also apply to multilane highways where staged construction includes a two-lane two-way operation as an initial stage. Whether auxiliary lanes are provided, however, depends on the time lag proposed between the initial stage and the final stage of construction. (2) Vertical Curves Figure 650-1 4 gives the length of crest vertical curve needed to provide passing sight distance for two-lane highways. The distance from Figure 650-9 and the equations in Figure 650-4, using 3.50 feet for both h 1 and h 2, may also be used to determine the minimum length of vertical curve to provide the required passing sight distance. Sag vertical curves
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are not a restriction to passing sight distance. (3) Horizontal Curves Passing sight distance can be restricted on the inside of a horizontal curve by roadside objects that are 3.50 feet or more above the roadway surface. Use the distance from Figure 650-9 and the equation in Figure 650-7 to determine whether the object is close enough to the roadway to be a restriction to passing sight distance. The equation assumes that the curve length is greater than the sight distance. Where the curve length is less than the sight distance, the desired sight distance may be available with a lesser M distance. Design Manual M 21-01 Sight Distance May 2006 Page 650-7 (4) No-Passing Zone Markings Knowledge of the practices used for marking no-passing zones on two-lane roads is helpful in designing a safe highway. The values in Figure 650-9 are the passing sight distances starting at the point the pass begins. The values in the MUTCD are lower than the Figure 650-9 values. They are for no-passing zone marking limits and start at the point the safe pass must be completed. The MUTCD values are not to be used directly in design, but are discussed for the designer’s recognition of locations requiring no-passing pavement markings. Sections of highway providing passing sight distance in the range of values between the distances in Figure 650-9 and MUTCD values require careful review by the designer. ## 650.06 Decision Sight Distance Decision sight distance values are greater than stopping sight distance values because they give the driver an additional margin for error and afford sufficient length to maneuver at the same or reduced speed rather than to just stop. Provide decision sight distance where highway features create the likelihood for error in information reception, decision making, or control actions. Example highway features
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include interchanges; intersections; changes in cross section (such as at toll plazas and drop lanes); and areas of concentrated demand where sources of information compete (for example, those from roadway elements, traffic, traffic control devices, and advertising signs). If possible, locate these highway features where decision sight distance can be provided. If this is not possible, use suitable traffic control devices and positive guidance to give advanced warning of the conditions. Use the decision sight distances in Figure 650-1 0 where highway features require complex driving decisions. > Design Speed (mph) Decision Sight Distance for Maneuvers (ft) ABCDE > 30 220 490 450 535 620 35 275 590 525 625 720 40 330 690 600 715 825 45 395 800 675 800 930 50 465 910 750 890 1030 55 535 1030 865 980 1135 60 610 1150 990 1125 1280 65 695 1275 1050 1220 1365 70 780 1410 1105 1275 1445 75 875 1545 1180 1365 1545 80 970 1685 1260 1455 1650 Decision Sight Distance > Figure 650-10 The maneuvers in Figure 650-1 0 are as follows: A. Rural stop B. Urban stop C. Rural speed/path/direction change D. Suburban speed/path/direction change E. Urban speed/path/direction change Decision sight distance is calculated using the same criteria as stopping sight distance: h1=3.50 feet and h2=0.50 foot. Use the equations in Figures 650-4, 5, and 7 to determine the decision sight distance for crest vertical curves, sag vertical curves, and horizontal curves. ## 650.07 Documentation The list of documents that are to be preserved in the Design Documentation Package (DDP) or the Project File (PF) can be found on the following web site: > Sight Distance Design Manual M 21-01 Page 650-8 May 2006 > 25 mph, S=155 ft 10 98765432100500 1000 1500 2000 2500 3000 > Length of Vertical
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Curve, L (ft) Algebraic Differance in Grade, A (%) > 30 mph, S=200 ft 35 mph, S=250 ft 40 mph, S=305 ft 45 mph, S=360 ft 50 mph, S=425 ft 55 mph, S=495 ft 60 mph, S=570 ft 65 mph, S=645 ft 70 mph, S=730 ft 75 mph, S=820 ft 80 mph, S=910 ft The minimum length can also be determined by multiplying the algebraic difference in grades by the K C value from Figure 650‑1 (L=K C*A). Both the figure and the equation give approximately the same length of curve. Neither use the S>L equation. * This chart is based on a 0.50‑foot object height. When a higher object height is allowed (see 650.04(3) for guidance), the equations in Figure 650‑4 must be used. 25 mph, S=155 ft 10 98765432100 500 1000 1500 2000 2500 3000 Length of Vertical Curve, L (ft) Algebraic Differance in Grade, A (%) 30 mph, S=200 ft 35 mph, S=250 ft 40 mph, S=305 ft 45 mph, S=360 ft 50 mph, S=425 ft 55 mph, S=495 ft 60 mph, S=570 ft 65 mph, S=645 ft 70 mph, S=730 ft 75 mph, S=820 ft 80 mph, S=910 ft Stopping Sight Distance for Crest Vertical Curves Figure 650-11 Design Manual M 21-01 Sight Distance May 2006 Page 650-9 The minimum length can also be determined by multiplying the algebraic difference in grades by the K Svalue from Figure 650‑ Error! Reference source not found. (L=K S*A). Both the figure and equation give approximately the same length of curve. Neither use the S>L equation. > 0200 400 600 800 1000 1200 1400 1600 1800 2000 012345678910 > Length of Vertical Curve, L (ft) Algebraic Differance in Grade, A (%) > 30 mph, S=200 ft 40 mph, S=305 ft 45 mph, S=360 ft 50 mph, S=425 ft 55
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mph, S=495 ft 60 mph, S=570 ft 65 mph, S=645 ft 70 mph, S=730 ft 75 mph, S=820 ft 25 mph, S=155 ft 35 mph, S=250 ft 80 mph, S=910 ft The minimum length can also be determined by multiplying the algebraic difference in grades by the K S value from Figure 650-1 (L=K S*A). Both the figure and equation give approximately the same length of curve. Neither use the S>L equation. The minimum length can also be determined by multiplying the algebraic difference in grades by the K Svalue from Figure 650‑ Error! Reference source not found. (L=K S*A). Both the figure and equation give approximately the same length of curve. Neither use the S>L equation. 0 200 400 600 800 1000 1200 1400 1600 1800 2000 012345678910 Length of Vertical Curve, L (ft) Algebraic Differance in Grade, A (%) > 30 mph, S=200 ft 40 mph, S=305 ft 45 mph, S=360 ft 50 mph, S=425 ft 55 mph, S=495 ft 60 mph, S=570 ft 65 mph, S=645 ft 70 mph, S=730 ft 75 mph, S=820 ft 25 mph, S=155 ft 35 mph, S=250 ft 80 mph, S=910 ft Stopping Sight Distance for Sag Vertical Curves Figure 650-12 Sight Distance Design Manual M 21-01 Page 650-10 May 2006 Horizontal Stopping Sight Distance > Figure 650-13a When h 2 =2.00 ft, objects between 2.00 ft and 2.75 ft above the centerline of the inside lane might be a sight obstruction. (See Figure 650‑13b for guidance.) 30 mph, S=200 ft 25 mph, S=155 ft 50 mph, S=425 ft 45 mph, S=360 ft 0 1000 2000 3000 4000 5000 6000 010 20 30 40 50 60 Curve Radius, R (ft) Lateral Clearance to Obstruction, M (ft) 40 mph, S=305 ft 55 mph, S=495 ft 60 mph, S=570 ft 65 mph, S=645 ft
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70 mph, S=730 ft 75 mph, S=820 ft 35 mph, S=250 ft 80 mph, S=910 ft 2.00 ft and 2.75 ft above the center-Design Manual M 21-01 Sight Distance May 2006 Page 650-11 Horizontal Stopping Sight Distance > Figure 650-13b When ¸¸¹·¨¨©§ ! > s > o ½C 0.75X 2h , roadside object is a sight obstruction. Where: M = Lateral clearance for sight distance (feet) (see Figure 650‑7) C s = Stopping sight distance chord (feet) X = Distance from the sight obstruction to the end of the sight distance chord (feet) ho = Height of roadside object above the centerline of the inside lane (feet) ML of lane CRoadside object between 2.00' & 2.75' Line of sight Edge of roadway 2.75' at the midpoint h 2=2.00' h 1=3.50' h oXC sSight Distance Design Manual M 21-01 Page 650-12 May 2006 Where S>L Where S>L > A > 2800 ‑2S LA1400 2LS Where S A2800L S L = Curve length (ft) A = Algebraic grade difference (percent) S = Sight distance (ft) 10 Where S>L A2800 ‑2S L A > 1400 2LS Where S A2800L S L = Curve length (ft) A = Algebraic grade difference (percent) S = Sight distance (ft) 10 Where SL A2800 ‑2S L A1400 2LS Where S 2800 AS L2 > A2800L S L = Curve length (ft) A = Algebraic grade difference (percent) S = Sight distance (ft) 10 Where S>L A2800 ‑2S L A1400 2LS Where S A2800L S L = Curve length (ft) A = Algebraic grade difference (percent) S = Sight distance (ft) 10 L = Curve length (ft) A = Algebraic grade difference (percent) S = Sight distance (ft) Passing Sight Distance for Crest Vertical Curves > Figure 650-14 10 98765432100 1000 2000 3000 4000 5000 6000
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7000 8000 9000 10,000 Length of Vertical Curve, L (ft) Algebraic Differance i n Gr ade, A (%) > 25 mph, S=900 ft 30 mph, S=1090 ft 35 mph, S=1280 ft 40 mph, S=1470 ft 45 mph, S=1625 ft 50 mph, S=1835 ft 55 mph, S=1985 ft 70 mph, S=2480 ft 60 mph, S= 2135 ft 65 mph, S=2285 ft Where S>L A2800 ‑2S L A1400 2LS Where S A2800L S L = Curve length (ft) A = Algebraic grade difference (percent) S = Sight distance (ft) 10 Design Manual Roadside Safety May 2006 Page 700-1 Chapter 700 Roadside Safety 700.01 General 700.02 References 700.03 Definitions 700.04 Clear Zone 700.05 Hazards to Be Considered for Mitigation 700.06 Median Considerations 700.07 Other Roadside Safety Features 700.08 Documentation ## 700.01 General Roadside safety addresses the area outside of the roadway and is an important component of total highway design. There are numerous reasons why a vehicle leaves the roadway. Regardless of the reason, a forgiving roadside can reduce the seriousness of the consequences of a roadside encroachment. From a safety perspective, the ideal highway has roadsides and median areas that are flat and unobstructed by hazards. Elements such as side slopes, fixed objects, and water are potential hazards that a vehicle might encounter when it leaves the roadway. These hazards present varying degrees of danger to the vehicle and its occupants. Unfortunately, geography and economics do not always allow ideal highway conditions. The mitigative measures to be taken depend on the probability of an accident occurring, the likely severity, and the available resources. In order of preference, mitigative measures are: removal, relocation, reduction of impact severity (using breakaway features or making it traversable), and shielding with a traffic barrier. Consider cost (initial and life cycle costs) and maintenance requirements in addition
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to accident severity when selecting a mitigative measure. Use traffic barriers only when other measures cannot reasonably be accomplished. See Chapter 710 for additional information on traffic barriers. ## 700.02 References A Policy on Geometric Design of Highways and Streets (Green Book), AASHTO, 2001 Revised Code of Washington (RCW) 47.24.020(2), “Jurisdiction, control” RCW 47.32.130, “Dangerous objects and structures as nuisances” City and County Design Standards (contained in the Local Agency Guidelines, M 36-63), WSDOT Roadside Design Guide, AASHTO, 2002 Roadside Manual , M 25-30, WSDOT Standard Plans for Road, Bridge, and Municipal Construction (Standard Plans), M 21-01, WSDOT ## 700.03 Definitions ADT The average daily traffic for the design year under consideration. backslope A sideslope that goes up as the distance increases from the roadway (cut slopes). clear run-out area The area beyond the toe of a nonrecoverable slope available for safe use by an errant vehicle. clear zone The total roadside border area, starting at the edge of the traveled way, available for use by errant vehicles. This area may consist of a shoulder, a recoverable slope, a nonrecoverable slope, and/or a clear run-out area. The clear zone cannot contain a critical fill slope. critical fill slope A slope on which a vehicle is likely to overturn. Slopes steeper than 3H:1V are considered critical fill slopes. Design Clear Zone The minimum target value used in highway design. foreslope A sideslope that goes down as the distance increases from the roadway (fill slopes and ditch inslopes). Roadside Safety Design Manual Page 700-2 May 2006 hazard A side slope, a fixed object, or water that, when struck, can result in unacceptable impact forces on the vehicle occupants or place the occupants in a hazardous position. A hazard can be either natural or manmade. nonrecoverable slope A slope on which an errant
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vehicle will continue until it reaches the bottom, without having the ability to recover control. Fill slopes steeper than 4H:1V, but no steeper than 3H:1V, are considered nonrecoverable. recoverable slope A slope on which the driver of an errant vehicle can regain control of the vehicle. Slopes of 4H:1V or flatter are considered recoverable. recovery area The minimum target value used in highway design when a fill slope between 4H:1V and 3H:1V starts within the Design Clear Zone. traffic barrier A longitudinal barrier, including bridge rail or an impact attenuator, used to redirect vehicles from hazards located within an established Design Clear Zone, to prevent median crossovers, to prevent errant vehicles from going over the side of a bridge structure, or (occasionally), to protect workers, pedestrians, or bicyclists from vehicular traffic. traveled way The portion of the roadway intended for the movement of vehicles, exclusive of shoulders and lanes for parking, turning, and storage for turning. ## 700.04 Clear Zone A clear roadside border area is a primary consideration when analyzing potential roadside and median hazards (as defined in 700.05). The intent is to provide as much clear, traversable area for a vehicle to recover as practical. The Design Clear Zone is used to evaluate the adequacy of the existing clear area and proposed modifications of the roadside. When considering the placement of new objects along the roadside or median, evaluate the potential for impacts and try to select locations with the least likelihood of an impact by an errant vehicle. (1) Design Clear Zone on All Limited Access State Highways and Other State Highways Outside Incorporated Cities and Towns Evaluate the Design Clear Zone when the Clear Zone column on the design matrices (see Chapter 325) indicates evaluate upgrade (EU) or Full Design Level (F) or when considering the
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placement of a new fixed object on the roadside or median. Use the Design Clear Zone Inventory form (Figures 700-2a & 2b) to identify potential hazards and propose corrective actions. Guidance for establishing the Design Clear Zone for highways outside of incorporated cities is provided in Figure 700-1. This guidance also applies to limited access state highways within the city limits. Providing a clear recovery area that is consistent with this guidance does not require any additional documentation. However, there might be situations where it is not practical to provide these recommended distances. In these situations, document the decision as an evaluate upgrade or deviation as discussed in Chapter 330. For additional Design Clear Zone guidance relating to roundabouts, see Chapter 915. While not required, the designer is encouraged to evaluate potential hazards even when they are beyond the Design Clear Zone distances. For state highways that are in an urban environment but outside of an incorporated city, evaluate both median and roadside clear zones as discussed above using Figure 700-1. However, there might be some flexibility in establishing the Design Clear Zone in urbanized areas adjacent to incorporated cities and towns. To achieve this flexibility, an evaluation of the impacts including safety, aesthetics, the environment, economics, modal needs, and access control can be used to establish the Design Clear Zone. This discussion, analysis, and agreement must take place early in the consideration of the median and roadside designs. An agreement on the responsibility for these median and roadside sections must be formalized with the city and/or county. The justification for the design decision for the selected Design Clear Zone must be documented as part of a project or corridor analysis. (See Chapter 330.) Design Manual Roadside Safety May 2006 Page 700-3 (2) Design Clear Zone Inside Incorporated Cities and
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Towns For managed access state highways within an urban area, it is recognized that in many cases it will not be practical to provide the Design Clear Zone distances shown in Figure 700-1. Roadways within an urban area generally have curbs and sidewalks and might have objects such as trees, poles, benches, trash cans, landscaping, and transit shelters along the roadside. (a) Roadside. For managed access state highways, it is the city’s responsibility to establish an appropriate Design Clear Zone in accordance with guidance contained in the City and County Design Standards. Document the Design Clear Zone established by the city in the Design Documentation Package. (b) Median. For managed access state highways with raised medians, the median’s Design Clear Zone is evaluated using Figure 700-1. In some instances, a median analysis will show that certain median designs provide significant benefits to overall corridor or project operations. In these cases, flexibility in establishing the Design Clear Zone is appropriate. To achieve this flexibility, an evaluation of the impacts (including safety, aesthetics, the environment, economics, modal needs, and access control) can be used to establish the median clear zone. This discussion, analysis, and agreement must take place early in the consideration of the flexible median design. An agreement on the responsibility for these median sections must be formalized with the city. The justification for the design decision for the selected Design Clear Zone must be documented as part of a project or corridor analysis. (See Chapter 330.) (3) Design Clear Zone and Calculations The Design Clear Zone guidance provided in Figure 700-1 is a function of the posted speed, side slope, and traffic volume. There are no distances in the table for 3H:1V fill slopes. Although fill slopes between 4H:1V and 3H:1V are considered traversable if free of fixed objects, these
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slopes are defined as nonrecoverable slopes. A vehicle might be able to begin recovery on the shoulder, but will be unable to further this recovery until reaching a flatter area (4H:1V or flatter) at the toe of the slope. Under these conditions, the Design Clear Zone distance is called a recovery area. The method used to calculate the recovery area and an example are shown in Figure 700-3. For ditch sections, the following criteria determine the Design Clear Zone: (a) For ditch sections with foreslopes 4H:1V or flatter (see Figure 700-4, Case 1, for an example) the Design Clear Zone distance is the greater of the following: • The Design Clear Zone distance for a 10H:1V cut section based on speed and the average daily traffic (ADT). • A horizontal distance of 5 f ee t beyond the beginning of the backslope . When a backslope steeper than 3H:1V continues for a horizontal distance of 5 f ee t beyond the beginning of the backslope, it is not necessary to use the 10H:1V cut slope criteria. (b) For ditch sections with foreslopes steeper than 4H:1V, and backslopes steeper than 3H:1V the Design Clear Zone distance is 10 f ee t horizontal beyond the beginning of the backslope . (See Figure 700-4, Case 2, for an example.) (c) For ditch sections with foreslopes steeper than 4H:1V and backslopes 3H:1V or flatter, the Design Clear Zone distance is the distance established using the recovery area formula (Figure 700-3). (See also Figure 700-4, Case 3, for an example.) ## 700.05 Hazards to Be Considered for Mitigation There are three general categories of hazards: side slopes, fixed objects, and water. The following sections provide guidance for determining when these obstacles present a significant hazard to an errant motorist. In addition, several conditions require special
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consideration: • Locations with high accident rate histories. • Locations with pedestrian and bicycle usage. See Chapters 1020, “Bicycle Facilities,” and 1025, “Pedestrian Design Considerations.” Roadside Safety Design Manual Page 700-4 May 2006 • Playgrounds, monuments, and other locations with high social or economic value . • Redirectional land forms, also referred to as earth berms, were installed to mitigate hazards located in depressed medians and at roadsides. They were constructed of materials that provided support for a traversing vehicle. With slopes in the range of 2H:1V to 3H:1V, they were intended to redirect errant vehicles. The use of redirectional land forms has been discontinued as a means for mitigating fixed objects. Where redirectional land forms currently exist as mitigation for a fixed object, ensure that the hazard they were intended to mitigate is removed, relocated, made crashworthy, or shielded with barrier. Landforms may be used to provide a smooth surface at the base of a rock cut slope. Use of a traffic barrier for hazards other than those described below requires justification in the Design Documentation Package. (1) Side Slopes (a) Fill Slopes. Fill slopes can present a hazard to an errant vehicle with the degree of severity dependent upon the slope and height of the fill. Providing fill slopes that are 4H:1V or flatter can mitigate this hazard. If flattening the slope is not feasible or cost effective, the installation of a barrier might be appropriate. Figure 700-5 represents a selection procedure used to determine whether a fill side slope constitutes a hazard for which a barrier is a cost-effective mitigation. The curves are based on the severity indexes and represent the points where total costs associated with a traffic barrier are equal to the predicted accident cost associated with selected slope heights without traffic barrier. If the
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ADT and height of fill intersect on the “Barrier Recommended” side of the embankment slope curve, then provide a barrier if flattening the slope is not feasible or cost effective. Do not use Figure 700-5 for slope design. Design guidance for slopes is in Chapters 430 and 640. Also, if the figure indicates that barrier is not recommended at an existing slope, that result is not justification for a deviation. For example, if the ADT is 4,000 and the embankment height is 10 f ee t, barrier will be cost effective for a 2H:1V slope, but not for a 2.5H:1V slope. This process only addresses the potential hazard of the slope. Obstacles on the slope can compound the hazard. Where barrier is not cost effective, use the recovery area formula to evaluate fixed objects on critical fill slopes less than 10 f ee t high. (b) Cut Slopes. A cut slope is usually less of a hazard than a traffic barrier. The exception is a rock cut with a rough face that might cause vehicle snagging rather than providing relatively smooth redirection. Analyze the potential motorist risk and the benefits of treatment of rough rock cuts located within the Design Clear Zone. A cost-effectiveness analysis that considers the consequences of doing nothing, removal, or smoothing of the cut slope, and all other viable options to reduce the severity of the hazard, can be used to determine the appropriate treatment. Also consider options to reduce the potential for roadway departures. Some potential options are: • Graded landform along the base of a rock cut. • Flexible barrier. • More rigid barrier. • Rumble strips. Conduct an individual investigation for each rock cut or group of rock cuts. Select the most cost-effective treatment. (2) Fixed Objects Consider the following objects for mitigation:
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• Wooden poles or posts with cross sectional area greater than 16 square inches that do not have breakaway features. • Nonbreakaway steel sign posts. • Nonbreakaway light standards. • Trees having a diameter of 4 inches or more measured at 6 inches above the ground surface. Design Manual Roadside Safety May 2006 Page 700-5 • Fixed objects extending above the ground surface by more than 4 inches; for example, boulders, concrete bridge rails, signal and electrical cabinets, piers, and retaining walls. • Existing guardrail that does not conform to current design guidance. (See Chapter 710.) • Drainage items, such as culvert and pipe ends. Mitigate hazards that exist within the Design Clear Zone when feasible. Although limited in application, there may be situations where removal of a hazard outside of the R.O.W . is appropriate. The possible mitigative measures are listed below in order of preference. • Remove. • Relocate. • Reduce impact severity (using a breakaway feature). • Shield the object by using longitudinal barrier or impact attenuator. (a) Trees. When evaluating new plantings or existing trees, consider the maximum allowable diameter of 4 inches measured at 6 inches above the ground when the tree has matured. When removing trees within the Design Clear Zone, complete removal of stumps is preferred. However, to avoid significant disturbance of the roadside vegetation, larger stumps may be mitigated by grinding or cutting them flush to the ground and grading around them. See the Roadside Manual for further guidance on the treatment of the disturbed roadside. (b) Mailboxes. Ensure that all mailboxes located within the Design Clear Zone have supports and connections as shown in the Standard Plans. The height from the ground to the bottom of the mailbox is 3 feet 3 inches. This height may vary from 3 feet 3
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inches to 4 feet if requested by the mail carrier. If the desired height is to be different from 3 feet 3 inches provide the desired height in the contract plans. See Figure 700-6 for installation guidelines. In urban areas where sidewalks are prevalent, contact the postal service to determine the most appropriate mailbox location. Locate mailboxes on limited access highways in accordance with Chapter 1430 “Limited Access”. A turnout, as shown on Figure 700-6, is not required on limited access highways with shoulders of 6 feet or more where only one mailbox is to be installed. On managed access highways, mailboxes must be on the right-hand side of the road in the direction of travel of the postal carrier. Avoid placing mailboxes along high-speed, high-volume highways. Locate Neighborhood Delivery and Collection Box Units (NDCBUs) outside the Design Clear Zone. (c) Culvert Ends. Provide a traversable end treatment when the culvert end section or opening is on the roadway side slope and within the Design Clear Zone. This can be accomplished for small culverts by beveling the end to match the side slope, with a maximum of 4 inches extending out of the side slope. Bars might be necessary to provide a traversable opening for larger culverts. Place bars in the plane of the culvert opening in accordance with the Standard Plans when: 1. Single cross culvert opening exceeds 40 inches measured parallel to the direction of travel. 2. Multiple cross culvert openings that exceed 30 inches each, measured parallel to the direction of travel. 3. Culvert approximately parallel to the roadway that has an opening exceeding 24 inches measured perpendicular to the direction of travel. Bars are permitted where they will not significantly affect the stream hydraulics and where debris drift is minor. Consult the regional Maintenance Office to
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verify these conditions. If debris drift is a concern, consider options to reduce the amount of debris that can enter the pipe. (See the Hydraulics Manual ). Other treatments are extending the culvert to move the end outside the Design Clear Zone or installing a traffic barrier. Roadside Safety Design Manual Page 700-6 May 2006 (d) Sign Posts. Whenever possible, locate signs behind existing or planned traffic barrier installations to eliminate the need for breakaway posts. Place them at least 25 f ee t from the end of the barrier terminal and with the sign face behind the barrier. When barrier is not present, use terrain features to reduce the likelihood of an errant vehicle striking the sign posts. Whenever possible, depending on the type of sign and the sign message, adjust the sign location to take advantage of barrier or terrain features. This will reduce accident potential and, possibly, future maintenance costs. See Chapter 820 for additional information regarding the placement of signs. Sign posts with cross sectional areas greater than 16 square inches that are within the Design Clear Zone and not located behind a barrier must have breakaway features as shown in the Standard Plans. (e) Traffic Signal Standards/Posts/Supports. Breakaway signal posts generally are not practical or desirable. Since these supports are generally located at intersecting roadways, there is a higher potential for a falling support to impact vehicles and/or pedestrians. In addition, signal supports that have overhead masts may be too heavy for a breakaway design to work properly. Other mitigation such as installing a traffic barrier is also very difficult. With vehicles approaching the support from many different angles, a barrier would have to surround the support and would be subject to impacts at high angles. Additionally, barrier can inhibit pedestrian movements. Therefore, barrier is
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generally not an option. However, since speeds near signals are generally lower, the potential for a severe impact is reduced. For these reasons, the only mitigation is to locate the support as far from the traveled way as possible. In locations where signals are used for ramp meters, the supports can be made breakaway as shown on the Standard Plan. (f) Fire Hydrants. Fire Hydrants are allowed on WSDOT right of way by franchise or permit. Fire hydrants that are made of cast iron can be expected to fracture on impact and can therefore be considered a breakaway device. Any portion of the hydrants that will not be breakaway must not extend more then 4 inches above the ground. In addition, the hydrant must have a stem that will shut off water flow in the event of an impact. Mitigate all other hydrants. (g) Utility Poles. Since utilities often share the right of way, utility objects such as poles will often be located along the roadside. It is undesirable/impractical to install barrier for all of these objects so mitigation is usually in the form of relocation (underground or to the edge of the right of way) or delineation. In some instances where there is a history of impacts with poles and relocation is not possible, a breakaway design might be appropriate. Contact Headquarters Design for information on breakaway features. Coordinate with the Utilities Office where appropriate. (h) Light Standards. Provide breakaway light standards unless fixed light standards can be justified. Fixed light standards may be appropriate in areas of extensive pedestrian concentrations, such as adjacent to bus shelters. Document the decision to use fixed bases in the Design Documentation Package. (3) Water Water with a depth of 2 f ee t or more and located with a likelihood of encroachment
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by an errant vehicle must be considered for mitigation on a project-by-project basis. Consider the length of time traffic is exposed to this hazard and its location in relationship to other highway features such as curves. Analyze the potential motorist risk and the benefits of treatment of bodies of water located within the Design Clear Zone. A cost-effectiveness analysis that considers the consequences of doing nothing versus installing a longitudinal barrier can be used to determine the appropriate treatment. For fencing considerations along water features, see Chapter 1460. Design Manual Roadside Safety May 2006 Page 700-7 ## 700.06 Median Considerations Medians must be analyzed for the potential of an errant vehicle to cross the median and encounter oncoming traffic. Median barriers are normally used on limited access, multilane, high-speed, high traffic volume highways. These highways generally have posted speeds of 45 mph or greater. Median barrier is not normally placed on collectors or other state highways that do not have limited access control. Providing access through median barrier requires openings and, therefore, end-treatments. Provide median barrier on full access control, multilane highways with median widths of 50 fee t or less and posted speeds of 45 mph or more. Consider median barrier on highways with wider medians or lower posted speeds when there is a history of cross median accidents. When installing a median barrier, provide left-side shoulder widths as shown in Chapters 430 and 440 and shy distance as shown in Chapter 710. Consider a wider shoulder area where the barrier will cast a shadow on the roadway and hinder the melting of ice. See Chapter 640 for additional criteria for placement of median barrier. See Chapter 710 for information on the types of barriers that can be used. See Chapter 650 for lateral clearance on the inside of
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a curve to provide the required stopping sight distance. When median barrier is being placed in an existing median, identify the existing crossovers and enforcement observation points. Provide the necessary median crossovers in accordance with Chapter 960, considering enforcement needs. Chapter 1050 provides guidance on HOV enforcement. ## 700.07 Other Roadside Safety ## Features (1) Rumble Strips Rumble strips are grooves or rows of raised pavement markers placed perpendicular to the direction of travel to alert inattentive drivers. There are three kinds of rumble strips: (a) Roadway rumble strips are placed across the traveled way to alert drivers approaching a change of roadway condition or a hazard that requires substantial speed reduction or other maneuvering. Examples of locations where roadway rumble strips may be used are in advance of: • Stop controlled intersections. • Port of entry/customs stations. • Lane reductions where accident history shows a pattern of driver inattention. They may also be placed at locations where the character of the roadway changes, such as at the end of a freeway. Contact the Headquarters Design Office for additional guidance on the design and placement of roadway rumble strips. Document justification for using roadway rumble strips. (b) Shoulder rumble strips are placed on the shoulders just beyond the traveled way to warn drivers when they are entering a part of the roadway not intended for routine traffic use. Shoulder rumble strips may be used when an analysis indicates a problem with run-off-the- road accidents due to inattentive or fatigued drivers. A comparison of rolled-in and milled-in Shoulder Rumble Strips (SRS) has determined that milled-in rumble strips, although more expensive, are more cost effective. Milled-in rumble strips are recommended. When SRS are used, discontinue them where no edge stripe is present such as at intersections and where curb and gutter are
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present. Where bicycle travel is allowed, discontinue SRS at locations where shoulder width reductions can cause bicyclists to move into or across the area where rumble strips would normally be placed, such as shoulders adjacent to bridges with reduced shoulder widths. SRS patterns vary depending on the likelihood of bicyclists being present along the highway shoulder, and whether they are placed on divided or undivided highways. Rumble strip patterns for undivided highways are shallower and may be Roadside Safety Design Manual Page 700-8 May 2006 narrower than patterns used on divided highways. They also provide gaps in the pattern, providing opportunities for bicycles to move across the pattern without having to ride across the grooves. There are four shoulder rumble strip patterns. Consult the Standard Plans for the patterns and construction details. 1. Divided Highways SRS are required on both the right and left shoulders of rural Interstate highways. Consider them on both shoulders of rural divided highways. Use the Shoulder Rumble Strip Type 1 pattern on divided highways. Omitting SRS on rural highways is a design exception (DE) under any one of the following conditions: • When another project scheduled within two years of the proposed project will overlay or reconstruct the shoulders or will use the shoulders for detours. • When a pavement analysis determines that installing SRS will result in inadequate shoulder strength. • When overall shoulder width will be less than 4 f ee t wide on the left and 6 f ee twide on the right. 2. Undivided Highways SRS are not required on undivided highways, but may be used where run-off-the-road accident experience is high. SRS usage on the shoulders of undivided highways demands strategic application because bicycle usage is more prevalent along the shoulders of the undivided highway system. Rumble strips affect the
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comfort and control of bicycle riders; consequently, their use is to be limited to highway corridors that experience high levels of run-off-the-road accidents. Apply the following criteria in evaluating the appropriateness of rumble strips on the shoulders of undivided highways. • Use on rural roads only. • Ensure shoulder pavement is structurally adequate to support milled rumble strips. • Posted speed is 45 mph or greater. • Ensure that at least 4 feet of usable shoulder remains between the rumble strip and the outside edge of shoulder. If guardrail or barrier is present, increase the dimension to 5 feet of usable shoulder. • Preliminary evaluation indicates a run-off-the-road accident experience of approximately 0.6 crashes per mile per year, or approximately 34 crashes per 100 million miles of travel. (These values are intended to provide relative comparison of crash experience and are not to be used as absolute guidance on whether rumble strips are appropriate.) • Do not place shoulder rumble strips on downhill grades exceeding 4% for more than 500 f ee t in length along routes where bicyclists are frequently present. • An engineering analysis indicates a run-off-the-road accident experience considered correctable by shoulder rumble strips. • Consult the regional members of the Washington Bicycle and Pedestrian Advisory Committee to determine bicycle usage along a route, and involve them in the decision-making process when considering rumble strips along bike touring routes or other routes where bicycle events are regularly held. The Shoulder Rumble Strip Type 2 or Type 3 pattern is used on highways with minimal bicycle traffic. When bicycle traffic on the shoulder is high, the Shoulder Rumble Strip Type 4 pattern is used. Shoulder rumble strip installation considered at any other locations must involve the WSDOT Bicycle and Pedestrian Advisory Committee as a partner in the decision-making
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process. Consult the following web site for guidance on conducting an engineering analysis: > RoadsideSafety/Chapter700/Chapter700B.htm Design Manual Roadside Safety May 2006 Page 700-9 (c) Centerline rumble strips are placed on the centerline of undivided highways to alert drivers that they are entering the opposing lane. They are applied as a countermeasure for crossover accidents. Centerline rumble strips are installed with no differentiation between passing permitted and no passing areas. Pavement marking should be refreshed when removed by centerline rumble strips. Drivers tend to move to the right to avoid driving on centerline rumble strips. Narrow lane and shoulder widths may lead to dropping a tire off the pavement when drivers have shifted their travel path. Centerline rumble strips are inappropriate when the combined lane and shoulder widths in each direction is less than twelve feet. See Chapters 430 and 440 for guidance on lane and shoulder width. Consider short sections of roadway that are below this width only when added for route continuity. Apply the following criteria in evaluating the appropriateness of centerline rumble strips: • An engineering analysis indicates a crossover accident history with collisions considered correctable by centerline rumble strips. Review the accident history to determine the frequency of collisions with contributing circumstances such as inattention, apparently fatigued, apparently asleep, over centerline, or on wrong side of road. • Centerline rumble strips are most appropriate on rural roads, but with special consideration may also be appropriate for urban roads. Some concerns specific to urban areas are noise in densely populated areas, the frequent need to interrupt the rumble strip pattern to accommodate left turning vehicles, and a reduced effectiveness at lower speeds (35 MPH and below). • Ensure the roadway pavement is structurally adequate to support milled rumble strips. Consult the region’s Materials Engineer to verify pavement
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adequacies. • Centerline rumble strips are not appropriate where two-way left-turn lanes exist. (2) Headlight Glare Considerations Headlight glare from opposing traffic can cause safety problems. Glare can be reduced by the use of wide medians, separate alignments, earth mounds, plants, concrete barrier, and by glare screens. Consider long term maintenance when selecting the treatment for glare. When considering earth mound and planting to reduce glare, see the Roadside Manual for additional guidance. When considering glare screens, see Chapter 650 for lateral clearance on the inside of a curve to provide the required stopping sight distance. In addition to reducing glare, taller concrete barriers also provide improved crash performance for larger vehicles such as trucks. Glare screen is relatively expensive and its use must be justified and documented. It is difficult to justify the use of glare screen where the median width exceeds 20 f ee t, the ADT is less than 20,000 vehicles per day, or the roadway has continuous lighting. Consider the following factors when assessing the need for glare screen: • Higher rate of night accidents compared to similar locations or statewide experience. • Higher than normal ratio of night to day accidents. • Unusual distribution or concentration of nighttime accidents. • Over representation of older drivers in night accidents. • Combination of horizontal and vertical alignment, particularly where the roadway on the inside of a curve is higher than the roadway on the outside of the curve. • Direct observation of glare. • Public complaints concerning glare. The most common glare problem is between opposing main line traffic. Other conditions for which glare screen might be appropriate are: • Between a highway and an adjacent frontage road or parallel highway, especially where opposing headlights might seem to be on the wrong side of the driver. Roadside
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Safety Design Manual Page 700-10 May 2006 • At an interchange where an on-ramp merges with a collector distributor and the ramp traffic might be unable to distinguish between collector and main line traffic. In this instance, consider other solutions, such as illumination. • Where headlight glare is a distraction to adjacent property owners. Playgrounds, ball fields, and parks with frequent nighttime activities might benefit from screening if headlight glare interferes with these activities. There are currently three basic types of glare screen available: chain link (see Standard Plans), vertical blades, and concrete barrier. (See Figure 700-7.) When the glare is temporary (due to construction activity), consider traffic volumes, alignment, duration, presence of illumination, and type of construction activity. Glare screen may be used to reduce rubbernecking associated with construction activity, but less expensive methods, such as plywood that seals off the view of the construction area, might be more appropriate. ## 700.08 Documentation A list of documents that are required to be preserved in the Design Documentation Package (DDP) or the Project File (PF) is on the following website: > Design Manual Roadside Safety May 2006 Page 700-11 Design Clear Zone Distances for State Highways Outside Incorporated Cities** (In feet from edge of traveled way***) Posted Speed mph Average Daily Traffic Cut Section (Backslope ) Fill Section (H:V) (H:V) 3:1 4:1 5:1 6:1 8:1 10:1 3:1 4:1 5:1 6:1 8:1 10:1 35 or Less The Design Clear Zone distance is 10 feet Under 250 10 10 10 10 10 10 * 13 12 11 11 10 251-800 11 11 11 11 11 11 * 14 14 13 12 11 40 801-2000 12 12 12 12 12 12 * 16 15 14 13 12 2001-6000 14 14 14 14 14 14 * 17 17 16 15 14 Over 6000
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15 15 15 15 15 15 * 19 18 17 16 15 Under 250 11 11 11 11 11 11 * 16 14 13 12 11 251-800 12 12 13 13 13 13 * 18 16 14 14 13 45 801-2000 13 13 14 14 14 14 * 20 17 16 15 14 2001-6000 15 15 16 16 16 16 * 22 19 17 17 16 Over 6000 16 16 17 17 17 17 * 24 21 19 18 17 Under 250 11 12 13 13 13 13 * 19 16 15 13 13 251-800 13 14 14 15 15 15 * 22 18 17 15 15 50 801-2000 14 15 16 17 17 17 * 24 20 18 17 17 2001-6000 16 17 17 18 18 18 * 27 22 20 18 18 Over 6000 17 18 19 20 20 20 * 29 24 22 20 20 Under 250 12 14 15 16 16 17 * 25 21 19 17 17 251-800 14 16 17 18 18 19 * 28 23 21 20 19 55 801-2000 15 17 19 20 20 21 * 31 26 23 22 21 2001-6000 17 19 21 22 22 23 * 34 29 26 24 23 Over 6000 18 21 23 24 24 25 * 37 31 28 26 25 Under 250 13 16 17 18 19 19 * 30 25 23 21 20 251-800 15 18 20 20 21 22 * 34 28 26 23 23 60 801-2000 17 20 22 22 23 24 * 37 31 28 26 25 2001-6000 18 22 24 25 26 27 * 41 34 31 29 28 Over 6000 20 24 26 27 28 29 * 45 37 34 31 30 Under 250 15 18 19 20 21 21 * 33 27 25 23 22 251-800 17
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20 22 22 24 24 * 38 31 29 26 25 65 801-2000 19 22 24 25 26 27 * 41 34 31 29 28 2001-6000 20 25 27 27 29 30 * 46 37 35 32 31 Over 6000 22 27 29 30 31 32 * 50 41 38 34 33 Under 250 16 19 21 21 23 23 * 36 29 27 25 24 251-800 18 22 23 24 26 26 * 41 33 31 28 27 70 801-2000 20 24 26 27 28 29 * 45 37 34 31 30 2001-6000 22 27 29 29 31 32 * 50 40 38 34 33 Over 6000 24 29 31 32 34 35 * 54 44 41 37 36 * When the fill section slope is steeper than 4H:1V but net steeper than 3H:1V, the Design Clear Zone distance is modified by the recovery area formula (Figure 700-3) and is referred to as the recovery area. The basic philosophy behind the recovery area formula is that the vehicle can traverse these slopes but cannot recover (control steering) and, therefore, the horizontal distance of these slopes is added to the Design Clear Zone distance to form the recovery area. ** This figure also applies to limited access state highways in cities and median areas on managed access state highways in cities. See 700.04 for guidance on managed access state highways within incorporated cities. *** See 700.03 for the definition of traveled way. Design Clear Zone Distance Table Figure 700-1 Roadside Safety Design Manual Page 700-12 May 2006 Design Clear Zone Inventory Form Figure 700-2a > DOT Form 410-026 EF Revised 9/02 > Design Clear Zone Inventory > Region SR Control Section MP to MP Project Title Project Number Date Responsible Unit > Item Number MP to MP Distance From Traveled
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Way Description Corrective Actions Considered (2) Estimated Cost to Correct Correction Planned (1) Yes No L R > (1) Only one “Yes” or “No” per item number. Corrections not planned must be explained on reverse side. > (2) A list of Location 1 & 2 Utility Objects to the forwarded to the region Utility Office for coordination per Control Zone G uidelines. Design Manual Roadside Safety May 2006 Page 700-13 Design Clear Zone Inventory Form Figure 700-2b > Item Number Reasons for Not Taking Corrective Action > DOT Form 410-026 EF Revised 9/02 Roadside Safety Design Manual Page 700-14 May 2006 Recovery Area > Figure 700-3 * Recovery area normally applies to slopes steeper than 4H:1V, but no steeper than 3H:1V. For steeper slopes, the recovery area formula may be used as a guide if the embankment height is 10 f eet or less. Formula: Recovery area = (shoulder width) + (horizontal distance) + (Design Clear Zone distance - shoulder width) Example: Fill section (slope 3H:1V or steeper) Conditions: Speed – 45 mph Traffic – 3000 ADT Slope – 3H:1V Criteria: Slope 3H:1V – use Recovery area formula Recovery area = (shoulder width) + (horizontal distance) + (Design Clear Zone distance - shoulder width) = 8 + 12 + (17-8) = 29 f eet Design Manual Roadside Safety May 2006 Page 700-15 Cut section with ditch (fore slope 4H:1V or flatter) Conditions: Speed - 55 mph Traffic - 4200 ADT Slope - 4H:1V Criteria: Greater of (1) Design Clear Zone for 10H:1V Cut Section, 23 f eet (2) 5 f ee t horizontal beyond beginning of back slope, 22 f eet Design Clear Zone = 23 f eet Case 1 Cut section with ditch (fore slope 3H:1V or steeper and back slope steeper than 3H:1V) Conditions: NA Criteria: 10 f
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ee t horizontal beyond beginning of back slope Design Clear Zone = 19 f eet Case 2 Cut section with ditch (fore slope 3H:1V or steeper and back slope not steeper than 3H:1V) Conditions: Speed - 45 mph Traffic - 3000 ADT Foreslope - 2H:1V Back slope 4H:1V Criteria: Use recovery area formula Recovery Area = (shoulder width) + (horizontal distance) + (Design Clear Zone distance - shoulder width) = 6 + 6 + (15 - 6) = 21 f eet Case 3 Design Clear Zone for Ditch Sections > Figure 700-4 Cut section with ditch (fore slope 4H:1V or flatter) (1) Design Clear Zone for 10H:1V Cut Section, 23 ft (2) 5 ft horizontal beyond beginning of back slope, 22 ft Case 1 Cut section with ditch (fore slope 3H:1V or steeper and back slope steeper than 3H:1V) Case 2 Cut section with ditch (fore slope 3H:1V or steeper and back slope not steeper than 3H:1V) Criteria: Use recovery area formula Recovery Area = (shoulder width) + (horizontal distance) + (Design Clear Zone distance - > Design Clear Zone = 23 ft Edge of traveled way 4H:1V 3H:1V 8 ft 6 ft shld 3 ft Design Clear Zone = 19 ft Edge of traveled w ay 3H:1V 2H:1V 10 ft 6ft 3ft shld Recovery Area = 21 ft Edge of traveled way 2H:1V 4H:1V 6 ft 6 ft shld Cut section with ditch (fore slope 4H:1V or flatter) (1) Design Clear Zone for 10H:1V Cut Section, 23 ft (2) 5 ft horizontal beyond beginning of back slope, 22 ft Case 1 Cut section with ditch (fore slope 3H:1V or steeper and back slope steeper than 3H:1V) Case 2 Cut section with ditch (fore slope 3H:1V or steeper and back slope not steeper than 3H:1V) Criteria: Use recovery area formula
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Recovery Area = (shoulder width) + (horizontal distance) + (Design Clear Zone distance - > Design Clear Zone = 23 ft Edge of traveled way 4H:1V 3H:1V 8 ft 6 ft shld 3 ft > Design Clear Zone = 19 ft Edge of traveled w ay 3H:1V 2H:1V 10 ft 6ft 3ft shld Recovery Area = 21 ft Edge of traveled way 2H:1V 4H:1V 6 ft 6 ft shld Cut section with ditch (fore slope 4H:1V or flatter) (1) Design Clear Zone for 10H:1V Cut Section, 23 ft (2) 5 ft horizontal beyond beginning of back slope, 22 ft Case 1 Cut section with ditch (fore slope 3H:1V or steeper and back slope steeper than 3H:1V) Case 2 Cut section with ditch (fore slope 3H:1V or steeper and back slope not steeper than 3H:1V) Criteria: Use recovery area formula Recovery Area = (shoulder width) + (horizontal distance) + (Design Clear Zone distance - > Design Clear Zone = 23 ft Edge of traveled way 4H:1V 3H:1V 8 ft 6 ft shld 3 ft Design Clear Zone = 19 ft Edge of traveled w ay 3H:1V 2H:1V 10 ft 6ft 3ft shld > Recovery Area = 21 ft Edge of traveled way 2H:1V 4H:1V 6 ft 6 ft shld Roadside Safety Design Manual Page 700-16 May 2006 Guidelines for Embankment Barrier Figure 700-5 Design Manual Roadside Safety May 2006 Page 700-17 Mailbox Location and Turnout Design Figure 700-6 Roadside Safety Design Manual Page 700-18 May 2006 Glare Screens Figure 700-8 Roadside Safety Design Manual Page 700-16 English Version August 1997 Glare Screens Figure 700-7 Chain Link Glare Screens Figure 700-8 Vertical Blades Glare Screens Figure 700-8 Concerete Barrier Design Manual M 22-01 Impact Attenuator Systems May 2006 Page 720-1 Chapter 720 Impact Attenuator Systems 720.01 Impact Attenuator Systems 720.02 Design Criteria
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720.03 Selection 720.04 Documentation ## 720.01 Impact Attenuator Systems Impact attenuator systems are protective systems that prevent an errant vehicle from impacting a hazard by either gradually decelerating the vehicle to a stop when hit head-on or by redirecting it away from the hazard when struck on the side. These barriers are used for rigid objects or hazardous conditions that cannot be removed, relocated, or made breakaway. Approved systems are shown in Figures 720-2a through 720-4b and on the WSDOT Headquarters (HQ) Design Office web page at: > RoadsideSafety/Chapter720/Chapter720B.ht m (1) Permanent Installations For systems used in permanent installations, a description of the system’s purpose, parts, and function, as well as requirements for transition, foundation, and slope, are provided as follows and in Figure 720-5: (a) Crash Cushion Attenuating Terminal (CAT-350) 1. Purpose: The CAT-350 is an end treatment for W-beam guardrail. It can also be used for concrete barrier if a transition is provided. 2. Description: The system consists of slotted W-beam guardrail mounted on both sides of breakaway timber posts. Steel sleeves with soil plates hold the timber posts in place. (See Figure 720-2a.) 3. Function : When hit head-on, the slotted guardrail is forced over a pin that shears the steel between the slots. This shearing dissipates the energy of the impact. 4. Foundation: Concrete footings or foundations are not required. 5. Slope: 10H:1V or flatter slope between the edge of the traveled way and the near face of the unit. 6. Manufacturer/Supplier: Trinity Industries, Inc. (b) Brakemaster 350 1. Purpose: The Brakemaster 350 system is an end treatment for W-beam guardrail. It can also be used for concrete barrier if a transition is provided. 2. Description: The system contains an embedded anchor assembly, W-beam fender panels, transition strap, and diaphragm. (See Figure 720-2a.) 3. Function:
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The system uses a brake and cable device for head-on impacts and for redirection. The cable is embedded in a concrete anchor at the end of the system. 4. Foundation: A concrete foundation is not required for this system, but a paved surface is recommended. 5. Slope: 10H:1V or flatter slope between the edge of the traveled way and the near face of the unit. 6. Manufacturer/Supplier: Energy Absorption Systems (c) QuadTrend 350 1. Purpose: The QuadTrend 350 is an end treatment for 2-foot-8-inches-high concrete barriers. The system’s short length allows it to be used at the ends of bridges where the installation of a beam guardrail transition and terminal is not feasible. 2. Description: This system consists of telescoping quadruple corrugated fender panels mounted on steel breakaway posts. (See Figure 720-2a.) 3. Function: Sand-filled boxes attached to the posts dissipate a portion of the energy of an impact. An anchored cable installed behind the fender panels directs the vehicle away from the barrier end. Impact Attenuator Systems Design Manual M 22-01 Page 720-2 May 2006 4. Foundation: The system is installed on a concrete foundation to support the steel posts. 5. Slope: A 6H:1V or flatter slope is required behind the barrier to allow for vehicle recovery. 6. Manufacturer/Supplier: Energy Absorption Systems (d) Universal TAU-II 1. Purpose: The Universal TAU-II crash cushion system is an end treatment for concrete barrier, beam guardrail, and fixed objects up to 8 feet wide. 2. Description: The system is made up of independent collapsible bays containing energy-absorbing cartridges that are guided and supported during a head-on hit by high strength galvanized steel cables and thrie beam rail panels. Each bay is composed of overlapping thrie beam panels on the sides and structural support diaphragms on the ends. Structural support diaphragms are attached to
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two cables running longitudinally through the system and attached to foundations at each end of the system. (See Figure 720-2c.) 3. Function: Overlapping panels, structural support diaphragms, cable supports, cables, and foundation anchors allow the system to resist angled impacts and mitigate head-on impacts. 4. Foundation: The system is installed on a concrete foundation or asphaltic concrete foundations conforming to the manufacturer’s recommendations. 5. Slope: 10H:1V or flatter slope between the edge of the traveled way and the near face of the unit. 6. Manufacturer/Supplier: Barrier Systems, Inc. (e) QuadGuard 1. Purpose: The QuadGuard is an end treatment for concrete barrier and beam guardrail and is also used to mitigate fixed objects up to 10 feet wide. 2. Description: The system consists of a series of Hex-Foam cartridges surrounded by a framework of steel diaphragms and quadruple corrugated fender panels. (See Figure 720-2b.) 3. Function: The internal shearing of the cartridges and the crushing of the energy absorption material absorb impact energy from end-on hits. The fender panels redirect vehicles impacting the attenuator on the side. 4. Foundation: The system is installed on a concrete foundation. 5. Slope: If the site has excessive grade or cross slope, additional site preparation or modification to the units in accordance with the manufacturer’s literature is required. Excessive is defined as steeper than 8% for the QuadGuard. 6. Manufacturer/Supplier: Energy Absorption Systems (f) QuadGuard Elite 1. Purpose: The QuadGuard Elite is an end treatment for concrete barrier and beam guardrail and is also used for fixed objects up to 7 feet 6 inches wide. 2. Description: The system consists of telescoping quadruple corrugated fender panels mounted on both sides of a series of polyethylene cylinders. (See Figure 720-2b.) 3. Function: The cylinders are compressed during a head-on impact and will return to their original
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shape when the system is reset. It is anticipated that this system will require very few replacement parts or extensive repair. 4. Foundation: The system is installed on a concrete foundation. 5. Slope: If the site has excessive grade or cross slope, additional site preparation or modification to the units in accordance with the manufacturer’s literature is required. Excessive is defined as steeper than 8% for the QuadGuard Elite. 6. Manufacturer/Supplier: Energy Absorption Systems Design Manual M 22-01 Impact Attenuator Systems May 2006 Page 720-3 (g) Reusable Energy Absorbing Crash Terminal (REACT 350) 1. Purpose: The REACT 350 is an end treatment for concrete barriers and is also used for fixed objects up to 3 feet wide. 2. Description: The system consists of polyethylene cylinders with varying wall thickness, redirecting cables, a steel frame base, and a backup structure. (See Figure 720-2d.) 3. Function: The redirecting cables are anchored in the concrete foundation at the front of the system and in the backup structure at the rear of the system. When hit head-on, the cylinders compress, absorb the impact energy, and immediately return to much of their original shape, position, and capabilities. For side impacts, the cables restrain the system enough to prevent penetration and redirect the vehicle. It is anticipated that this system will require very few replacement parts or extensive repair. 4. Foundation: The system is installed on a concrete foundation. 5. Slope : If the site has excessive grade or cross slope, additional site preparation or modification to the units in accordance with the manufacturer’s literature is required. Excessive is defined as steeper than 8% for the REACT 350. 6. Manufacturer/Supplier: Energy Absorption Systems (h) (REACT 350 Wide) 1. Purpose: The REACT 350 Wide is a device that can be used to shield objects with widths up
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to 10 feet wide. 2. Description: The system consists of polyethylene cylinders with varying wall thickness, internal struts, space frame diaphragms, and a monorail. (See Figure 720-2d.) 3. Function: When hit head-on, the cylinders compress, absorb the impact energy, and immediately return to much of their original shape, position, and capabilities. For side impacts, the system is designed to restrain and redirect the vehicle. It is anticipated that this system will require very few replacement parts or extensive repairs. 4. Foundation: The system is installed on a concrete foundation. 5. Slope: If the site has excessive grade or cross slope, additional site preparation or modification to the units in accordance with the manufacturer’s literature is required. Excessive is defined as steeper than 8% for the REACT 350 Wide. 6. Manufacturer/Supplier: Energy Absorption Systems (i) Inertial Barrier Inertial barrier configurations are shown in the Standard Plans. If a situation is encountered the configurations in the Standard Plans are not appropriate, contact the HQ Design Office for further information. 1. Purpose: Inertial barrier is an end treatment for concrete barrier and is used to mitigate fixed objects. This system does not provide redirection from a side impact. 2. Description: This system consists of an array of plastic containers filled with varying weights of sand. (See Figure 720-2d.) 3. Function: The inertial barriers slow an impacting vehicle by the transfer of the momentum of the vehicle to the mass of the barrier. This system is not suitable where space is limited to less than the widths shown in the Standard Plans. Whenever possible, align inertial barriers so that an errant vehicle deviating from the roadway by 10° would be on a parallel path with the attenuator alignment. (See the Standard Plans .) In addition, inertial barriers do not provide any redirection and are
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not appropriate where high angle impacts are likely. Impact Attenuator Systems Design Manual M 22-01 Page 720-4 May 2006 4. Foundation : A concrete or paved surface is recommended. 5. Slope : If the site has excessive grade or cross slope, additional site preparation or modification to the units in accordance with the manufacturer’s literature is required. Excessive is defined as steeper than 5% for inertial barriers. (j) SCI100GM / SCI70GM 1. Purpose: The SCI100GM / SCI70GM are end treatments that can be used for concrete barrier and beam guardrail with widths up to 2 feet. 2. Description: The system for both models consists of telescoping quadruple corrugated fender panels mounted on both sides of a series of tubular steel support frames. (See Figure 720-2e.) 3. Function: A hydraulic cylinder is compressed during a head-on impact. 4. Foundation: The system is installed on a concrete or asphalt foundation. (See manufactures installation requirements for details.) 5. Slope: 12 H:1V or flatter slope between the edge of the traveled way and the near face of the unit. 6. Manufacturer/Supplier: Work Area Protection Corp. In addition to the systems approved above, the TRACC impact attenuator may be considered for permanent use, with the concurrence of Maintenance personnel. (2) Work Zone (Temporary) Installation Several of the impact attenuators previously listed under the heading “Permanent Installations” are also appropriate for use in work zones or other temporary locations. The following is a list of these devices: • QuadGuard • QuadGuard Elite • REACT 350 • REACT 350 Wide • Inertial Barriers • SCI100GM • SCI70GM The following systems are appropriate only in work zones or other temporary installations. A description of each work zone (or other temporary) system’s purpose, parts, and functionality, as well as requirements for transition, foundation, and slope, are provided as follows
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and in Figure 720-5: (a) ABSORB 350 1. Purpose: The ABSORB 350 is an end treatment limited to temporary installations for both concrete barrier and the Quickchange Moveable Barrier (QMB). 2. Description: The system contains water-filled Energy Absorbing Elements. Each element is 2 feet wide, 2 feet 8 inches high, and 3 feet 3 ½ inches long. (See Figure 720-3.) 3. Function: The low-speed (below 45 mph) system uses five Energy Absorbing Elements and the high-speed (45 mph and above) system uses eight. The energy of an impact is dissipated as the elements are crushed. 4. Foundation: The system does not require a paved foundation. 5. Slope: 10H:1V or flatter slope between the edge of the traveled way and the near face of the unit. 6. Manufacturer/Supplier: Barrier Systems, Inc. (b) Advanced Dynamic Impact Extension Module 350 (ADIEM 350) 1. Purpose: The ADIEM 350 is limited to temporary installations where vehicle speeds are 45 mph or less. It is generally used as an end treatment for concrete barrier. Currently, there are a few existing permanent units in service. It is permissible to reset these existing devices. However, some of these units may exhibit significant deterioration and replacement may be the appropriate option. Design Manual M 22-01 Impact Attenuator Systems May 2006 Page 720-5 2. Description: The system is 30 feet long and consists of 10 lightweight concrete modules on an inclined base. (See Figure 720-3.) 3. Functionality: An inclined base provides a track for placement of the modules and provides redirection for side impacts for roughly half the length. The energy of an impact is dissipated as the concrete modules are crushed. 4. Foundation: The system does not require a paved foundation. 5. Slope: If the site has excessive grade or cross slope, additional site preparation or modification to the
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units in accordance with the manufacturer’s literature is required. Excessive is defined as steeper than 8% for the ADIEM 350. 6. Manufacturer/Supplier: Trinity Industries, Inc. (c) QuadGuard CZ This system is like the permanent QuadGuard listed for permanent systems above except that it can be installed on a 6-inch-minimum-depth asphalt concrete surface that has a 6-inch-minimum-depth compacted base. (See Figure 720-2b.) (d) Reusable Energy Absorbing Crash Terminal (REACT 350) This is the same system listed for permanent systems above except that it can be installed on a 6-inch-minimum-depth asphalt concrete surface that has a 6-inch-minimum-depth compacted base. (See Figure 720-2d.) (e) Non-Redirecting Energy Absorbing Terminal (N-E-A-T) 1. Purpose: The N-E-A-T system is an end treatment for temporary concrete barrier where vehicle speeds are 45 mph or less. 2. Description: The N-E-A-T System’s cartridge weighs about 300 pounds and is 9 feet-8 inches long. The system consists of aluminum cells encased in an aluminum shell with steel backup, attachment hardware, and transition panels. It can be attached to the ends of New Jersey shaped portable concrete barrier and the QuickChange Moveable Barrier. (See Figure 720-3.) 3. Functionality: The energy of an impact is dissipated as the aluminum cells are crushed. 4. Foundation: The system does not require a paved foundation. 5. Slope: 10H:1V or flatter slope between the edge of the traveled way and the near face of the unit. 6. Manufacturer/Supplier: Energy Absorption Systems (f) Trinity Attenuating Crash Cushion (TRACC) 1. Purpose: The TRACC is an end treatment for concrete barriers. It is limited to use in construction or other work zones on a temporary basis. 2. Description: The 21-foot-long TRACC includes four major components: a pair of guidance tracks, an impact sled, intermediate steel frames, and 10 gauge W-beam fender panels. (See Figure 720-3.) 3. Functionality: The sled (impact
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face) is positioned over the upstream end of the guidance tracks and contains a hardened steel blade that cuts the metal plates on the sides of the guidance tracks as it is forced backward when hit head-on. 4. Foundation: The system requires a concrete foundation. 5. Slope: 10H:1V or flatter slope between the edge of the traveled way and the near face of the unit. 6. Manufacturer/Supplier: Trinity Industries, Inc. (g) Inertial Barrier This is the same system listed for permanent systems above. It is not suitable where space is limited to less than the widths shown in the Standard Plans. (See Figure 720-2d.) Impact Attenuator Systems Design Manual M 22-01 Page 720-6 May 2006 4. Foundation: The system is installed on a concrete or asphalt foundation. (See manufacturer’s installation requirements for details.) The unit is attached to the road surface with 30 to 34 anchors. 5. Slope: 12H:1V (8%) or flatter slope between the edge of the traveled way and the near face of the unit is required. In addition, if the slope varies (twists) more than 2% over the length of the system, a concrete leveling pad may be required. 6. Manufacture/Supplier: Energy Absorption Systems Inc. (3) Older Systems The following systems are in use on Washington State highways and may be left in place or reset. New installations of these systems require approval from the HQ Design Office. (a) Sentre The Sentre is a guardrail end treatment. Its overall length of 17 feet allowed it to be used where space was not available for a guardrail transition and terminal. The system is very similar to the QuadTrend 350 in both appearance and function except that it uses thrie beam fender panels instead of the quadruple corrugated panels. This system requires a transition when used to terminate rigid
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barriers. (See Figure 720-4a.) (b) TREND The TREND is an end treatment with a built-in transition and was used at the end of rigid barriers including bridge rails. The system is similar to the QuadTrend 350 except that it uses thrie beam fender panels. (See Figure 720-4a.) (c) G-R-E-A-T (Guard Rail Energy Absorption Terminal) This system was primarily used as an end treatment for concrete barrier. It is similar to the QuadGuard except that it uses thrie beam fender panels. (See Figure 720-4a.) (h) Truck Mounted Attenuator (TMA) TMAs are portable systems mounted on trucks. They are intended for use in work zones and for temporary hazards. (i) Triton CET 1. Purpose: The Triton CET is an end treatment limited to temporary concrete barrier installations. 2. Description: The system contains water-filled Energy Absorbing Elements. (See Figure 720-3.) 3. Function: The system uses six Energy Absorbing Elements. The energy of an impact is dissipated as the elements are crushed. 4. Foundation: The system does not require a paved foundation. 5. Slope: 10H:1V or flatter slope between the edge of the traveled way and the near face of the unit. 6. Manufacturer/Supplier: Energy Absorption, Inc. (j) QUEST 1. Purpose: The QUEST is an end treatment limited to temporary applications. This system is designed to shield hazards 2 feet or less in width. 2. Description: The system consists of two front anchor assemblies; a nose assembly containing an integrated trigger assembly; two shaper rail assemblies; a support rail assembly with two energy absorbing tube shapers; a diaphragm assembly; a bridge assembly; two rear rails; a freestanding backup assembly; and W-beam fender panels. Transition panels are required when traffic approaches from the rear of the unit. 3. Function: During head-on impacts, the Quest system telescopes rearward and energy is absorbed through momentum transfer, friction,
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and deformation. When impacted from the side, the QUEST System restrains lateral movement by dynamic tension developed between the end restraints. Design Manual M 22-01 Impact Attenuator Systems May 2006 Page 720-7 (d) Low Maintenance Attenuator System (LMA) The LMA is an end treatment for concrete barrier and beam guardrail and was used for fixed objects up to 3 feet wide. The system is similar to the QuadGuard Elite except that it uses thrie beam fender panels and rubber cylinders. See Figure 720-4b. (e) Hex-Foam Sandwich The Hex-Foam Sandwich system is an end treatment for beam guardrail and concrete barrier and was also used for fixed objects 3 feet or more in width. This system consists of a number of Hex-Foam cartridges containing an energy absorption material separated by a series of diaphragms and restrained by anchor cables. It is installed on a concrete slab. Impact energy is absorbed by the internal shearing of the cartridges and crushing of the energy absorption material. The lapped panels on the perimeter serve to redirect vehicles for side impacts. If the site has grade or cross slope in excess of 5%, additional site preparation or modification to the units in accordance with the manufacturer’s literature is required. (See Figure 720-4b.) ## 720.02 Design Criteria The following design criteria apply to all new or reset permanent and temporary impact attenuators. The design criteria also apply to existing systems to be left in place when the Barrier Terminals and Transition Sections columns on a design matrix applies to the project. (See Chapter 325.) Impact attenuators must be placed so that they do not present a hazard to opposing traffic. For median and reversible lane locations, the backup structure or attenuator-to-object connection must be designed to prevent opposing traffic from being snagged. It is desirable that
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all existing curbing be removed and the surface smoothed with asphalt or cement concrete pavement before an impact attenuator is installed. However, curbs 4 inches or less in height may be retained depending on the practicality of their removal. In general, attenuators are aligned parallel to the roadway except the inertial barriers. ## 720.03 Selection When selecting an impact attenuator system, consider the following: • Posted speed • Available space (length and width) • Maintenance costs • Initial cost • Duration (permanent or temporary use) • The portion of the impact attenuator that is redirective/nonredirective. (See figures 720-5 and 6.) It is very important for designers to consider the portion of an impact attenuator that will redirect vehicles during a side impact of the unit. It is crucial to consider that fixed objects, either permanent or temporary (such as construction equipment), should not be located behind the non-redirective portion of these devices. The posted speed is a consideration in the selection of the QuadGuard, REACT 350 Universal TAU-II and the Inertial Barrier systems. Use Figure 720-1 to select permanent system sizes required for the various posted speeds. > Posted Speed (mph) Quad Guard (Bays) Universal TAU-II (1) (Bays) REACT 350 (Cylinders) Inertial Barrier (Type) 40 or less 32-3 4145 43-4 6250 54-5 6355 65-7 6460 67-8 9565 87-8 9670 97-8 96(1) Dependent on the width of the system Impact Attenuator Sizes > Figure 720-1 If it is anticipated that a large volume of traffic will be traveling at speeds greater than the posted speed limit, then the next larger unit may be specified. Impact Attenuator Systems Design Manual M 22-01 Page 720-8 May 2006 For a summary of space and initial cost information related to the impact attenuator systems, see Figure 720-5. When considering maintenance costs, anticipate the average annual
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impact rate. If few impacts are anticipated, lower-cost devices such as inertial barriers might meet the need. Inertial barriers have the lowest initial cost and initial site preparation. However, maintenance will be costly and necessary after every impact. Labor and equipment are necessary to clean up the debris and install new containers (barrels). Also, inertial barriers must not be used where flying debris might be a danger to pedestrians. The REACT 350 and the QuadGuard Elite have a higher initial cost, requiring substantial site preparation, including a backup or anchor wall in some cases and cable anchorage at the front of the installation. However, repair costs are comparatively low, with labor being the main expense. Maintenance might not be required after minor side impacts with these systems. For new installations where at least one impact is anticipated per year, limit the selection of impact attenuators to the low maintenance devices (QuadGuard Elite and REACT 350). Consider upgrading existing ADIEM, G-R-E-A-T, and Hex-Foam impact attenuators with these low maintenance devices when the repair history shows one to two impacts per year over a three to five year period. In selecting a system, one consideration that must not be overlooked is how dangerous it will be for the workers making repairs. In areas with high exposure to danger, a system that can be repaired quickly is most desirable. Some systems require nearly total replacement or replacement of critical components (such as cartridges or braking mechanisms) after a head-on impact, while others only require resetting. It is very important to consider that each application is unique when selecting impact attenuators for use in particular applications. This applies to both permanent and temporary installations. When specifying the system or systems that can be used at a specific location, the list shown in Figure 720-5
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is to be used as a starting point. As the considerations discussed previously are analyzed, inappropriate systems may be identified and eliminated from further consideration. Systems that are not eliminated may be appropriate for the project. When the site conditions vary, it might be necessary to have more than one list of acceptable systems within a contract. Systems are not to be eliminated without documented reasons. Also, wording such as or equivalent is not to be used when specifying these systems. If only one system is found to be appropriate, then approval from the Assistant State Design Engineer of a public interest finding for the use of a sole source proprietary item is required. When a transition to connect with a concrete barrier (see Figure 720-5) is required, the transition type and connection must be specified and are included in the cost of the impact attenuator. (See Chapter 710 for information on the transitions and connections to be used.) Contractors can be given more flexibility in the selection of work zone (temporary) systems, since long-term maintenance and repair are not a consideration. ## 720.04 Documentation A list of documents that are to be preserved in the Design Documentation Package (DDP) or the Project File (PF) can be found is on the following web site: > Design Manual M 22-01 Impact Attenuator Systems May 2006 Page 720-9 Impact Attenuator Systems – Permanent Installations > Figure 720-2a CAT -350 Brakemaster QuadTrend 350 Impact Attenuator Systems Design Manual M 22-01 Page 720-10 May 2006 QuadGuard QuadGuard Elite Impact Attenuator Systems – Permanent Installations Figure 720-2b Design Manual M 22-01 Impact Attenuator Systems May 2006 Page 720-11 Impact Attenuator Systems – Permanent Installations Figure 720-2c Universal TAU -II Impact Attenuator Systems Design Manual M 22-01 Page 720-12 May 2006 REACT 350 Wide REACT
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350 Inertial Barrier Impact Attenuator Systems – Permanent Installations Figure 720-2d REACT 350 Wide Design Manual M 22-01 Impact Attenuator Systems May 2006 Page 720-13 Impact Attenuator Systems – Permanent Installations Figure 720-2e SCI100GM / SCI70GM Impact Attenuator Systems Design Manual M 22-01 Page 720-14 May 2006 Impact Attenuator Systems – Work Zone Installations Figure 720-3a ## ABSORB 350 ## ADIEM 350 QuadGuard CZ Design Manual M 22-01 Impact Attenuator Systems May 2006 Page 720-15 Impact Attenuator Systems – Work Zone Installations Figure 720-3b ## N-E-A-T ## TRACC ## Triton CET ## QUEST Impact Attenuator Systems Design Manual M 22-01 Page 720-16 May 2006 Impact Attenuator Systems – Older Systems Figure 720-4a Sentre TREND G-R-E-A-T Design Manual M 22-01 Impact Attenuator Systems May 2006 Page 720-17 Impact Attenuator Systems – Older Systems Figure 720-4b L.M.A. Hex-Foam Sandwich Impact Attenuator Systems Design Manual M 22-01 Page 720-18 May 2006 > Impact Attenuator Systems (All dimensions in feet) System (P) Permanent (T) Temporary (B) Both Approximate Outside Width (See Note 10) Approximate System Length (See Note 11) Transition to Rigid System Required? Distance Beyond Length of Need (See Figure 720-6) Initial Cost Category(1) CAT 350 (2) P 2.5 31.3 Y 18.8 ABrakemaster 350 (2) P 2.1 31.5 Y 15.8 AQuadTrend – 350 (6) P 1.3 20.0 N 10.5 AUniversal TAU-II P 2.9 - 8.7 12.0-26.0 (4) N 3.0 B(5) QuadGuard B 2.8-10.8 13.1-32.5 (4) N 3.3 B(5) QuadGuard Elite B 2.8-8.3 23.8-35.5 N 3.3 DREACT 350 B 4 13.8-30.2 (4) N 4.3 C(5) REACT 350 Wide B 5.7-10.7 30.8-34.8 Y 4.3 D(5) Inertial Barriers B 7 17.0-34.5 (4) N (3) A(5) SCI100GM B 3.1 21.5 Y 3 CSCI70GM (8) B 2.8 13.5 Y 3 BABSORB 350(9) T 2 19.0-32.0 Y (3) A(5) ADIEM 350 (7)(8) T 2.7 30 N 14.1 BQuadGuard CZ
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T 2.75-3.25 13.1-22.1 N 3.3 C (5) N-E-A-T(8) T 1.9 9.7 N (3) A(5) TRACC (12) T 2.6 21.3 N 8 BTriton CET (9) T 1.8 40 N (3) AQUEST T 2.8 22.2 Y 3.5 B Impact Attenuator Comparison > Figure 720-5a Design Manual M 22-01 Impact Attenuator Systems May 2006 Page 720-19 1) A ($5,000 to $10,000); B ($10,000 to $15,000); C ($15,000 to $25,000); D ($25,000 to $50,000). These are rough initial cost estimates - verify actual costs through manufacturers/suppliers. Some products are priced very close to the margin between cost categories. 2) Generally for use with double-sided beam guardrail. Use as an end treatment for concrete barrier requires a transition. 3) The N-E-A-T, inertial barriers, Triton CET, and ABSORB 350 may only be used beyond the required length of need. (4) For sizes or configuration type, see Figure 720-1. (5) The lengths of the Universal TAU-II, QuadGuard, QuadGuard Elite, REACT 350, REACT 350 Wide, ABSORB 350, QuadGuard CZ, and Inertial Barriers vary because their designs are dependent upon speed. Costs indicated are for a typical 60 mph design. In addition to length, several of the systems also vary in width. For estimating purposes, the following model widths were considered. • Universal TAU II – 24” • QuadGuard – 24” • QuadGuard Elite – 24” • REACT 350 Wide – 60” • QuadGuard CZ – 24” (6) Generally for use at the ends of bridges where installation of a beam guardrail transition and terminal is not feasible. (7) Generally for use with concrete barrier. Other uses may require a special transition design. (8) Use limited to highways with posted speeds of 45 mph or less. ((9) Test Level 3 version on high-speed facilities should be limited to locations where the likelihood of being hit is low. (10) The
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given dimension is the approximate outside width of each system. In most cases, this width is slightly wider than the effective width. To determine the width of an object that may be shielded refer to the manufacture’s specifications. (See the WSDOT Design Policy, Standards, & Safety Research Unit web site for links to this information.) (11) The given dimension is the approximate system length. The effective length may vary depending on such factors as the physical design and type of anchorage used. To determine the total length needed, refer to the manufacture’s specifications. (See the WSDOT Design Policy, Standards, & Safety Research Unit web site for links to this information.) (12) May be considered for permanent installations with concurrence of Maintenance personnel. Impact Attenuator Comparison Figure 720-5b Impact Attenuator Systems Design Manual M 22-01 Page 720-20 May 2006 Impact Attenuator Distance Beyond Length of Need Figure 720-6 Design Manual M 22-01 Delineation May 2006 Page 830-1 830.01 General 830.02 References 830.03 Definitions 830.04 Pavement Markings 830.05 Guideposts 830.06 Barrier Delineation 830.07 Object Markers 830.08 Wildlife Warning Reflectors 830.09 Documentation 830.01 General The primary function of delineation is to provide the visual information needed by a driver to operate a vehicle safely in a variety of situations. Delineation can be the marking of highways with painted or more durable pavement marking lines and symbols, guideposts, and other devices, such as curbs. (See Chapter 440.) These devices use retroreflectance, reflecting light from a vehicle’s headlights back to the driver, to enhance their visibility at nighttime. The Washington State Department of Transportation (WSDOT) uses the latest edition of the MUTCD as a guide for the design, location, and application of delineation. Delineation is a required safety item of work and is addressed on all projects. A decision to omit delineation work can only
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be justified if the existing delineation is unaffected by construction and an evaluation of accident rates clearly shows that delineation is not a contributing factor. It is important to maintain an adequate level of retroreflectivity for both traffic signs and traffic markings to enhance safety for motorists during hours of darkness and during adverse weather conditions. Consult with the region’s Traffic Operations Office early in the design process to ensure that the proposed delineation is compatible with WSDOT policy and region preference. These policies and preferences address both the type of markings and the material selection. # Chapter 830 Delineation 830.02 References Laws – Federal and state laws and codes that may pertain to this chapter include: Manual on Uniform Traffic Control Devices, USDOT, FHWA, National Advisory Committee on Uniform Traffic Control Devices, including the Washington State Modifications to the MUTCD, Chapter 468-95 Washington Administrative Code (WAC), (MUTCD) > htm Design Guidance – Design guidance included by reference within the text includes: Roadway Delineation Practices Handbook ,FHWA report, Washington, DC, 1994 Sign Fabrication Manual , M 55-05, WSDOT Standard Plans for Road, Bridge, and Municipal Construction (Standard Plans), M 21-01, WSDOT Supporting Information – Other resources used or referenced in this chapter include: NCHRP Synthesis 306, Long-Term Pavement Practices , Transportation Research Board ## 830.03 Definitions coefficient of retroreflection (R L) A measure of retroreflection. delineation Any method of defining the roadway operating area for the driver. durability A measure of a traffic line’s resistance to the wear and deterioration associated with abrasion and chipping . extrude A procedure for applying marking material to a surface by forcing the material through a die to give it a certain shape. glass beads Small glass spheres used in highway pavement markings to provide the necessary retroreflectivity. Delineation Design Manual M 22-01
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Page 830-2 May 2006 mcd/m 2/lux Pavement marking retroreflectivity is represented by the coefficient of retroreflected luminance (R L) measured in millicandelas per square meter. mil Unit of measurement equivalent to 0.001 inches. MUTCD Manual on Uniform Traffic Control Devices. pavement marking A colored marking applied to the pavement to provide drivers with guidance and other information. retroreflection The phenomenon of light rays striking a surface and being returned directly back to the source of light. retroreflectometer An instrument used to measure retroreflectivity. spraying A procedure for applying marking material to a surface as a jet of fine liquid particles. service life The service life of a pavement marking is the time or number of traffic passages required for its retroreflectivity to decrease from its initial value to a minimum threshold value indicating that the marking needs to be refurbished or replaced. traffic paint A pavement marking material that consists mainly of a binder and a solvent. The material is kept in liquid form by the solvent, which evaporates upon application to the pavement, leaving the binder to form a hard film. wet film thickness Thickness of a pavement marking at the time of application without glass beads. ## 830.04 Pavement Markings (1) Pavement Marking Types Pavement markings have specific functions: (1) they guide the movement of traffic, and (2) they promote safety on the highway. In some cases, they are used to supplement the messages of other traffic control devices. In other cases, markings are the only way to convey a message without distracting the driver. Pavement markings are installed and maintained to provide adequate performance year round. Adequate performance is defined as meaning the marking meets or exceeds standards of both daytime and nighttime visibility. Pavement markings are classified as either longitudinal or transverse. Centerlines, lane lines (where
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applicable), and edge lines (except as noted), are required on all paved state highways, unless an exception is granted by the State Traffic Engineer with justification. Guidelines for the application of various pavement markings are provided in the Standard Plans and the MUTCD. (a) Longitudinal pavement markings define the boundary between opposing traffic flows, and identify the edges of traveled way, multiple traffic lanes, turn lanes, and special use lanes. The Standard Plans show the dimensions of longitudinal pavement markings. Longitudinal pavement markings are as follows: barrier centerline A very wide (18 inches minimum, usually 20 inches—five 4-inch lines) solid yellow line or a combination of two single 4-inch solid yellow lines with yellow crosshatching between the lines with a total width not less than 18 inches used to separate opposing traffic movements where all movements over the line are prohibited. Barrier centerline locations require the approval of the region’s Traffic Engineer and Access Engineer. centerline A broken yellow line used to separate lanes of traffic moving in opposite directions, where passing in the opposing lane is allowed. dotted extension line A broken white or yellow line that is an extension of an edge line or centerline used at exit ramps, intersections on horizontal curves, multiple turn lanes, and other locations where the direction of travel for through traffic is unclear. double centerline Two parallel solid yellow lines used to separate lanes of traffic moving in opposite directions where passing in the opposing lane is prohibited. double lane line Two solid white lines used to separate lanes of traffic moving in the same direction where crossing the lane line marking is prohibited. double wide lane line Two solid wide white lines used to separate a concurrent preferential lane of traffic where crossing is prohibited. Design Manual M 22-01 Delineation May
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2006 Page 830-3 drop lane line A wide broken white line used in advance of a wide line to delineate a lane that ends at an off-ramp or intersection. edge line A solid white or yellow line used to define the outer edges of the traveled way. Edge lines are not required where curbs or sidewalks are 4 feet or less from the traveled way. lane line A broken white line used to separate lanes of traffic moving in the same direction. no-pass line A solid yellow line used in conjunction with a centerline where passing in the opposing lane is prohibited. reversible lane line Two broken yellow lines used to delineate a lane where traffic direction is periodically reversed. solid lane line A solid white line used to separate lanes of traffic moving in the same direction where crossing the lane line marking is discouraged. Note: While this marking is in the MUTCD, it may not be in wide use by WSDOT, as it is the same as the edge line. two-way left-turn centerline Two yellow lines, one solid and one broken, used to delineate each side of a two-way left-turn lane. wide broken lane line A wide broken white line used to designate a portion of a high occupancy vehicle (HOV) lane located on a divided highway where general purpose vehicles may enter to make an exit. wide dotted lane line A wide broken white line used to designate a portion of a high occupancy vehicle (HOV), or business access and transit (BAT) lane located on an arterial highway where general purpose vehicles may enter to make a turn at an intersection. wide lane line A wide solid white line used to separate lanes of traffic moving in the same direction at ramp connections, storage lanes at intersections,
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and high occupancy vehicle (HOV) lanes, or business access and transit (BAT) lanes, bike lanes, and other preferential lanes where crossing is discouraged. (b) Transverse pavement markings define pedestrian crossings and vehicle stopping points at intersections. They are also used to warn the motorist of approaching conditions, required vehicular maneuvers, or lane usage. Typical transverse pavement markings are as follows: access parking space symbol A white marking used to designate parking stalls provided for motorists with disabilities. The marking may have an optional blue background and white border. aerial surveillance marker White markings used at one-mile and one-half-mile intervals on sections of highways where the State Patrol uses airplanes to enforce speed limits. bicycle lane symbol A white marking consisting of a symbol of a bicyclist and an arrow used in a marked bike lane. (See the Standard Plans for an example of the bicycle lane symbol.) The bicycle lane symbol shall be placed immediately after an intersection and at other locations as needed. (See the MUTCD.) Typical spacing is 500 feet, with a maximum distance of 1,500 feet. crosswalk line A series of parallel solid white lines used to define a pedestrian crossing. drainage marking A white line used to denote the location of a catch basin, grate inlet, or other drainage feature in the shoulder of a roadway. HOV symbol A white diamond marking used for high occupancy vehicle lanes. The spacing of the markings is an engineering judgment based on the conditions of use. Typical spacing is 1,000 feet for divided highways and 500 feet for arterial highways. railroad crossing symbol A white marking used in advance of a railroad crossing where grade crossing signals or gates are located or where the posted speed of the highway is 40 mph or higher. stop line A solid white
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line used to indicate the stopping point at an intersection or railroad crossing. traffic arrow A white marking used in storage lanes and two-way left-turn lanes to denote the direction of turning movement. Arrows are also used at ramp terminals and intersections on divided highways to discourage wrong-way movements. Delineation Design Manual M 22-01 Page 830-4 May 2006 traffic letters White markings forming word messages, such as “ONLY,” used in conjunction with a traffic arrow at drop-lane situations. Traffic letters are not required for left- and right-turn storage lanes where the intended use of the lane is obvious. (2) Pavement Marking Materials Pavement markings are applied using various materials. These materials are divided into two categories: paint and plastic. When selecting the pavement marking material to use in a project, consider the initial cost of the material; its service life; the location; the traffic conditions; the snow and ice removal practices of the particular maintenance area; and the region’s ability to maintain the markings. Both painted and plastic pavement markings can accomplish the goal of providing a visible (daytime) and retroreflective (nighttime) pavement marking at the completion of a contract. The difference between the two marking materials is the projected service life of the markings. Paint used on sections of highway subjected to high traffic volumes and/or snow removal operations might have a service life of only two to three months. Maintenance crews cannot restripe a highway during winter months; therefore, if a painted marking wears out prematurely, the highway will not have a stripe until maintenance crews can restripe in April or May. When these conditions are encountered in a highway project, it is strongly recommended that the designer specify one of the more durable plastic marking materials and application types that will provide an adequate service life for
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the marking. For the recommended pavement marking material for different highway types and snow removal practices, see Figure 830-1. Consult with the region’s Traffic Office and Maintenance Office to select the best material for the project. (a) Paint. Paint is the most common pavement marking material. It is relatively easy to apply and dries quickly (30–90 seconds in warm, dry weather) after application. This allows the application to be a moving operation, which minimizes traffic control costs and delay to the roadway users. On construction contracts, paint is applied with two coats; the first coat is 10 mils thick, followed by a second coat 15 mils thick. The disadvantage of using paint as a pavement marking material is its short service life when subjected to traffic abrasion, sanding, or snow-removal activities. Specify paint only where it will have a service life that will provide a retroreflective stripe until the maintenance crews can repaint the line and extend its service life until the next repainting. Paint is one of two material types dependent upon the solids carrier: solvent or waterborne. The designer is encouraged to specify waterborne paint. Waterborne paints developed in the last ten years have proven to be more durable than solvent paints. Solvent paint is also subject to a monetary penalty because it contains a high level of volatile organic compounds (VOC). There is an Environmental Protection Agency (EPA) Clean Air Act penalty assessed on solvent paint that is passed on to those that purchase solvent paint in quantity. Durable waterborne paint or high-build waterborne paint (a recent development) allows a thicker application (20 to 30 mils), which provides additional service life. The additional thickness permits the use of larger glass beads that enhance wet night retroreflectivity. (b) Plastic. Plastic markings have a higher installation cost than paint.
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They can, however, be a more cost-effective measure than paint because of their longer service life. Plastic marking materials may provide a year-round retroreflective pavement marking, while paint may not last until the next restriping. Plastic marking materials currently listed in the Standard Specifications include the following: • Type A – Liquid Hot Applied Thermoplastic. Thermoplastic material consists of resins and filler materials in solid form at room temperature. The material is heated to a semi-liquid, molten state (400º Fahrenheit) and is then applied to the roadway by spray or extrusion methods. This material can be used for both transverse and longitudinal line applications. Special equipment is required for both the initial application and subsequent maintenance Design Manual M 22-01 Delineation May 2006 Page 830-5 renewal. Sprayed material can be applied at a thickness of 30 mils and dries in 30 to 60 seconds. The service life of material applied in this manner is slightly longer than that of paint. Extruded material is applied at a thickness of 125 mils and has a drying time of 15 minutes. This material can be applied as a flat line or it can be applied with ridges or bumps that enhance wet night visibility. These bumps produce a rumble effect similar to raised pavement markers when a vehicle crosses over the marking. • Type B – Preformed Fused Thermoplastic. This material consists of a mixture of pigment, fillers, resins, and glass beads that is factory produced in sheet form 125 mils thick. The material is applied by heating (drying) the pavement and top heating the material. The heating process fuses the preformed thermoplastic material to the pavement surface. These materials are available in white, yellow, blue, and other colors. These materials are used for transverse markings. • Type C – Cold Applied Preformed
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Tape. Preformed tape is composed of thermoplastic or other materials that are fabricated under factory conditions. After curing, the material is cut to size and shipped to the work site in rolls or in flat pieces. The material is then applied to the roadway with an adhesive on the underside of the tape. Preformed tape is available in a thickness of 60 mils, 90 mils, or 125 mils. (WSDOT does not currently specify 125 mil tape.) The most durable application of preformed tape is achieved when the tape is either inlaid (rolled) into hot asphalt and the top of the tape is flush with the surface of the pavement, or it is placed in a groove cut into the pavement surface and the top of the tape is slightly below the surface of the pavement. ASTM has classified preformed tape into two categories: Type 1 and Type 2. Type 1 tape has a profiled surface and a requirement to have a retroreflectivity of over 500 mcd/ m2/lux. Type 1 tape has proven to be very durable. It is used on high-volume, high-speed highways. Type 2 tape has a flat surface and a requirement to have a retroreflectivity of over 250 mcd/m 2/lux. Field tests show that Type 2 tape has a shorter service life than Type 1 tape. • Type D – Liquid Cold Applied Methyl Methacrylate (MMA). Methyl methacrylate can be applied by either spraying or extrusion. Sprayed applications can be one or two coats, 30 to 45 mils thick. Extruded applications are 90 mils thick for dense asphalt or PCC pavement, or 120 mils thick for open-graded asphalt pavement. MMA can also be extruded using specialized equipment to produce a textured line 150 mils thick. The material is not heated and can be applied within an approximate temperature
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range of 40º to 105º Fahrenheit, provided the pavement surface is dry. The material can be used for both transverse and longitudinal applications. The material can also be applied with bumps (Type D profiled) that slightly enhance wet night retroreflectivity. The bumps also produce the rumble effect similar to raised pavement markers. • Type E – Polyurea. Polyurea is a two-component, 100% solid coating designed as a fast-setting highway marking coating that provides durability and abrasion resistance. Polyurea is formulated to provide a simple volumetric mixing ratio of two volumes of Component A to one volume of Component B. Polyurea is typically sprayed at 20 to 25 mils thickness. (c) Glass Beads. Glass beads are small glass spheres used in highway markings to provide the necessary retroreflectivity. The beads are dropped onto the wet marking material immediately after it is applied (drop-on beads) or premixed into the marking material and dropped onto the wet marking material immediately after it is applied. Proper installation of glass beads is critical to achieving good pavement marking retroreflectivity. Each glass bead works like a light-focusing lens reflecting light back to the driver. Glass beads are embedded into the pavement marking material; for optimum performance, the bead is embedded between 55% and 60% of its diameter. Delineation Design Manual M 22-01 Page 830-6 May 2006 Large glass beads are effective when roads are wet. Large glass beads are not appropriate for paint as the paint is too thin to properly embed the large glass beads; therefore, WSDOT specifies small glass beads for paint applications. The use of large glass beads is limited to high-build waterborne paint and other materials with a thickness of at least 22 mils. (3) Pavement Marking Application Types There are five application types used for pavement markings. Most pavement marking applications
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are applied directly to the pavement surface. In steel bit snow plowing areas, the pavement markings may be inlaid or grooved to protect the markings. Pavement markings, because they are higher than the surrounding pavement surface, are subject to rapid wear caused by traffic and snowplows. As they wear, they lose visibility and retroreflectivity particularly in wet weather. Wear on the stripes can be greatly reduced and their service life considerably increased by placing them in a shallow groove in the surface of the pavement. The five application types for pavement markings are: • Flat Lines. Pavement marking lines with a flat surface. • Profiled Marking. A profiled pavement marking that consists of a base line thickness and a profiled thickness, which is a portion of the pavement marking line that is applied at a greater thickness than the base line thickness. Profiles are applied using the extruded method in the same application as the base line. The profiles may be slightly rounded if the minimum profile thickness is provided for the entire length of the profile. (See the Standard Plans for the construction details.) • Embossed Plastic Line. Embossed plastic lines consist of a flat line with transverse grooves. An embossed plastic line may also have profiles. (See the Standard Plans for the construction details.) • Inlaid Plastic Line. A line constructed by rolling Type C tape into Hot Mix Asphalt with the finish roller. Closely monitor the temperature of the mat to ensure compliance with the manufacturer’s recommendations. • Grooved Plastic Line. A line constructed by cutting a groove into the pavement surface and spraying, extruding, or gluing pavement marking material into the groove. The groove depth is dependent upon the material used, the pavement surface, and the location. The groove is typically in the range of 20
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to 250 mils deep and 4 inches wide. Coordinate with the region’s Traffic Office on the use and dimensions of grooved plastic line marking. (4) Raised Pavement Markers Raised Pavement Markers (RPMs) are installed as positioning guides with long line pavement markings. They can also be installed as a complete substitution for certain long line markings. RPMs have a service life of two years, and provide good wet night visibility and a rumble effect. RPMs are made from plastic materials and are available in three different types: • Type 1 markers are 4 inches in diameter, 3/4−inch high, and nonreflectorized • Type 2 markers are 4 inches wide, 2 1/2 to 4 inches long, 3/4−inch high, and reflectorized • Type 3 markers are 6, 8, 10, or 12 inches wide, 4 inches long, 3/4−inch high, and nonreflectorized Type 2 RPMs are not used as a substitute for right edge lines. They can only be used to supplement the right edge line markings at lane reductions, at sections with reduced lane widths such as narrow structures, and at the gore of exit ramps. All other applications supplementing right edge line markings require approval of the region’s Traffic Engineer. Type 3 RPMs are used in locations where additional emphasis is desired, including vehicle separations and islands. Approval by the region’s Traffic Engineer is required for all installations of Type 3 RPMs. Design Manual M 22-01 Delineation May 2006 Page 830-7 Reflectorized RPMs are not required for centerline and lane line applications in continuously illuminated sections of highway. However, if reflectorized RPMs are used at an intersection within an illuminated section, they are also provided throughout that section. For raised pavement marker application details, see the Standard Plans. (5) Recessed Raised Pavement Markers Recessed raised pavement markers (RRPMs) are raised pavement markers (RPMs)
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installed in a groove ground into the pavement in accordance with the Standard Plans. RRPMs provide guidance similar to RPMs in ice chisel and steel blade snow removal areas. RRPMs can also be used in rubber blade snow removal areas in accordance with region policy. RRPMs, when specified, are installed at the locations shown for Type 2W RPMs on multilane one-way roadways, and Type 2YY RPMs on two-lane two-way roadways. For recessed pavement marker application details, see the Standard Plans. ## 830.05 Guideposts (1) General Guideposts are retroreflective devices mounted to a support post installed at the side of the roadway to indicate alignment. They are considered to be guidance devices rather than warning devices. They are used as an aid to nighttime driving primarily on horizontal curves; all multilane divided highways; ramps; tangent sections where they can be justified due to snow, fog, or other reduced visibility conditions; and at intersections without illumination. The retroreflective device may be mounted on either a white or brown post. The types of guideposts and their application are as follows: (a) Type W guideposts have silver-white reflective sheeting, are facing traffic, and are used on the right side of divided highways, ramps, right-hand acceleration and deceleration lanes, intersections, and ramp terminals. (b) Type WW guideposts have silver-white reflective sheeting on both sides, and are used on the outside of horizontal curves on two-way, undivided highways. (c) Type Y guideposts have yellow reflective sheeting, are facing traffic, and are used on the left side of ramps, left-hand acceleration and deceleration lanes, ramp terminals, intersections on divided highways, median crossovers, and horizontal curves on divided highways. (d) Type YY guideposts have yellow reflective sheeting on both sides, and are used in the median on divided highways. (e) Type G1 guideposts have silver-white reflective sheeting on
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both sides, and green reflective sheeting below the silver-white sheeting on the side facing traffic. They are used at intersections of undivided highways without illumination. (f) Type G2 guideposts have silver-white reflective sheeting on both sides, and green reflective sheeting below the silver-white reflective sheeting on the back side. They are used at intersections of undivided highways without illumination. (2) Placement and Spacing Guideposts are placed not less than 2 feet nor more than 8 feet outside the outer edge of the shoulder. Place guideposts at a constant distance from the edge of the roadway. When an obstruction intrudes into this space, position the guideposts to smoothly transition to the inside of the obstruction. Guideposts are not required along continuously illuminated divided or undivided highways. (See Figure 830-2 for guidepost placement requirements.) The Standard Plans contain information on the different types and placement of guideposts. Delineation Design Manual M 22-01 Page 830-8 May 2006 ## 830.06 Barrier Delineation Traffic barriers are delineated where guideposts are required, such as bridge approaches, ramps, and other locations on unilluminated roadways. (See Figure 830-2.) At these locations, the barrier delineation has the same spacing as that of guideposts. Barrier delineation is also required when the traffic barrier is 4 feet or less from the traveled way. Use a delineator spacing of no more than 40 feet at these locations. Beam guardrail is delineated by either mounting flexible guideposts behind the rail or by attaching shorter flexible guideposts to the wood guardrail posts. Concrete barrier is delineated by placing retroreflective devices on the face of the barrier about 6 inches down from the top. Consider mounting these devices on the top of the barrier at locations where mud or snow accumulates against the face of the barrier. ## 830.07 Object Markers Object markers are used
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to mark obstructions within or adjacent to the roadway. The MUTCD details three types of object markers. The Type 3 object marker with yellow and black sloping stripes is the most commonly used object marker. The MUTCD contains criteria for the use of object markers to mark objects in the roadway and objects adjacent to the roadway. These criteria shall be followed in project design. The terminal ends of impact attenuators are delineated with modified Type 3 object markers. These are the impact attenuator markers in the Sign Fabrication Manual . When the impact attenuator is used in a roadside condition, the marker with diagonal stripes pointing downward toward the roadway is used. When the attenuator is used in a gore where traffic will pass on either side, the marker with chevron stripes is used. End of Roadway markers are similar to Type 1 object markers and are detailed in the MUTCD. They are used to alert users about the end of the roadway. The MUTCD criteria shall be followed in project design. ## 830.08 Wildlife Warning Reflectors Studies show that wildlife warning reflectors are ineffective at reducing the accident potential for motor vehicle/wildlife collisions. WSDOT policy is to no longer design, place, or maintain wildlife warning reflectors. ## 830.09 Documentation The list of documents that are to be preserved in the Design Documentation Package (DDP) or the Project File (PF) can be found on the following web site: > Design Manual M 22-01 Delineation May 2006 Page 830-9 Ice Chisel Snow Removal Areas Roadway Classification Marking Type (3) Centerlines (5) Lane Lines (5) Edge Lines Wide Lines Transverse Markings Interstate N.A. Grooved Plastic (1) Paint Paint Paint Major Arterial Paint & RRPMs (4) or Plastic (2) &RRPMs (4) Paint Paint Paint Paint Minor Arterial Paint Paint Paint Paint
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Paint Collector Paint Paint Paint Paint Paint Steel Blade Snow Removal Areas Roadway Classification Marking Type (3) Centerlines (5) Lane Lines (5) Edge Lines Wide Lines Transverse Markings Interstate-Urban N.A. Plastic (2) Paint or Plastic (2) Paint or Plastic (2) Paint or Plastic (2) Interstate-Rural N.A. Paint Paint or Plastic (2) Paint or Plastic (2) Paint or Plastic (2) Major Arterial Paint & RRPMs (4) or Plastic (2) &RRPMs (4) Paint Paint or Plastic (2) Paint or Plastic (2) Paint or Plastic (2) Minor Arterial Paint Paint Paint Paint or Plastic (2) Paint or Plastic (2) Collector Paint Paint Paint Paint or Plastic (2) Paint or Plastic (2) Rubber Blade Snow Removal Areas Roadway Classification Marking Type (3) Centerlines (5) Lane Lines (5) Edge Lines Wide Lines Transverse Markings Interstate-Urban N.A. PMMA (6) only or PMMA (6) & RPMs Paint or Plastic (2) Plastic (7) FMMA (8) Interstate-Rural N.A. MMA only or (8) MMA & RPMs Paint Plastic (2)(7) FMMA (8) Major Arterial Paint & RPMs or Plastic (2) & RPMs (7) Paint Plastic (7)(2) Plastic (2)(7) Minor Arterial Paint & RPMs Paint & RPMs Paint Plastic (2) Plastic (2) Collector Paint & RPMs Paint Paint Plastic (2) Plastic (2) Notes: (1) Grooved Plastic is a line constructed by cutting a groove into the pavement surface and spraying, extruding, or gluing pavement marking material into the groove. (2) Plastic refers to methyl methacrylate (MMA), thermoplastic, or preformed tape. (3) For RPM substitute applications and RPM applications supplementing paint or plastic, see the Standard Plans, Section M. (4) RRPMs refer to RPMs installed in a groove ground into the pavement. RRPMs are identified as ”Recessed Pavement Markers” in the Standard Specifications and the Standard Plans. (5) Type 2 RPMs are not required with painted or plastic centerline or lane line in
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illuminated sections. (6) PMMA refers to profiled methyl methacrylate. (7) Consult region striping policy. (8) FMMA refers to flat methyl methacrylate. Pavement Marking Material Guide Figure 830-1 Delineation Design Manual M 22-01 Page 830-10 May 2006 Highway Type Guideposts on Tangents (See Notes 1 & 3) Guideposts on Horizontal Curves (See Notes 1 & 3) Divided Highways With Continuous Illumination Main Line None None Bridge Approaches None None Intersections None None Lane Reductions Standard Plan, Section H Standard Plan, Section H Median Crossovers None None Ramps Standard Plan, Section H Standard Plan, Section H Divided Highways Without Continuous Illumination Main Line with RPMs None Standard Plan, Section H Main Line without RPMs Right Side Only (0.10 mile spacing) Standard Plan, Section H Bridge Approaches Standard Plan, Section H Standard Plan, Section H Intersections Standard Plan, Section H Standard Plan, Section H Lane Reductions Standard Plan, Section H Standard Plan, Section H Median Crossovers Standard Plan, Section H Standard Plan, Section H Ramps Standard Plan, Section H Standard Plan, Section H Undivided Highways With Continuous Illumination Main Line None None Bridge Approaches None None Intersections None None Lane Reductions Standard Plan, Section H Standard Plan, Section H Undivided Highways Without Continuous Illumination Main Line See Note 2 Standard Plan, Section H (See Note 2) Bridge Approaches Standard Plan, Section H Standard Plan, Section H Intersections with Illumination None None Intersections without Illumination Standard Plan, Section H Standard Plan, Section H Lane Reductions Standard Plan, Section H Standard Plan, Section H > Notes: > 1. For lateral placement of guideposts, see the Standard Plans, Section H. 2. Installation of guideposts on tangents and on the inside of horizontal curves is allowed at locations approved > by the region’s Traffic Engineer. 3. Barrier delineation is required when the traffic barrier is 4 feet
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or less from the roadway. Use delineator spacing > of 40 feet or less. Guidepost Placement > Figure 830-2 Design Manual M 22-01 Intersections At Grade May 2006 Page 910-1 910.01 General 910.02 References 910.03 Definitions 910.04 Design Considerations 910.05 Design Vehicle 910.06 Right-Turn Corners 910.07 Channelization 910.08 Roundabouts 910.09 U-Turns 910.10 Sight Distance at Intersections 910.11 Traffic Control at Intersections 910.12 Interchange Ramp Terminals 910.13 Procedures 910.14 Documentation ## 910.01 General Intersections are a critical part of highway design because of increased conflict potential. Traffic and driver characteristics, bicycle and pedestrian needs, physical features, and economics are considered during the design stage to develop channelization and traffic control to enhance safe and efficient multimodal traffic flow through intersections. This chapter provides guidance for designing intersections at grade, including at-grade ramp terminals. See the following chapters for additional information: Chapter Subject 915 Roundabouts 920 Road Approaches 940 Interchanges If an intersection design situation is not covered in this chapter, contact the Headquarters (HQ) Design Office, for assistance. ## 910.02 References Laws – Federal and state laws and codes that may pertain to this chapter include: Americans with Disabilities Act of 1990 (ADA) Manual on Uniform Traffic Control Devices for Streets and Highways , USDOT, FHWA; including the Washington State Modifications to the MUTCD , Chapter 468-95 WAC (MUTCD), > htm Washington Administrative Code (WAC) 468-18-040, “Design standards for rearranged county roads, frontage roads, access roads, intersections, ramps and crossings” WAC 468-52, “Highway access management— Access control classification system and standards” Design Guidance – Design guidance included by reference within the text includes: Local Agency Guidelines (LAG), M 36-63, WSDOT Standard Plans for Road, Bridge, and Municipal Construction (Standard Plans), M 21-01, WSDOT Supporting Information – Other resources used or referenced in this chapter include: A Policy on Geometric Design
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of Highways and Streets (Green Book), 2001, AASHTO Guidelines and Recommendations to Accommodate Older Drivers and Pedestrians ,FHWA-RD-01-051 , USDOT, FHWA, May 2001 Highway Capacity Manual (HCM), Special Report 209, Transportation Research Board, National Research Council Highway Research Record No. 211 Aspects of Traffic Control Devices , pp 1-18, “Volume Warrants for Left-Turn Storage Lanes at Unsignalized Grade Intersections.” Harmelink, M. D. NCHRP 279 Intersection Channelization Design Guide Roundabouts: An Informational Guide, FHWA-RD-00-067, USDOT, FHWA # Chapter 910 Intersections At Grade Intersections At Grade Design Manual M 22-01 Page 910-2 May 2006 ## 910.03 Definitions bulb out A curb and sidewalk bulge or extension out into the roadway used to decrease the length of a pedestrian crossing. (See chapter 1025.) conflict An event involving two or more road users, in which the action of one user causes the other user to make an evasive maneuver to avoid a collision. crossroad The minor roadway at an intersection. At a stopped controlled intersection, the crossroad has the stop. intersection angle The angle between any two intersecting legs at the point that the center lines intersect. intersection area The area of the intersecting roadways bounded by the edge of traveled ways and the area of the adjacent roadways to the end of the corner radii, any marked crosswalks adjacent to the intersection, or stop bar, but not less than 10 f ee t from the edge of shoulder of the intersecting roadway. See Figure 910-1. > Intersection Area 10 ' Intersection Area > Figure 910-1 intersection at grade The general area where a state route or ramp terminal is met or crossed at a common grade or elevation by another state route, a county road, or a city street. four leg intersection An intersection with four legs, as where two highways cross. tee
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(T) intersection An intersection with three legs in the general form of a “T.” split tee A four leg intersection with the cross road intersecting the through roadway at two tee intersections. The crossroad must be offset at least the width of the roadway. wye (Y) intersection An intersection with three legs in the general form of a “Y” and the angle between two legs is less than 60°. intersection leg Any one of the roadways radiating from and forming part of an intersection. entrance leg The lanes of an intersection leg for traffic entering the intersection. exit leg The lanes of an intersection leg for traffic leaving the intersection. Whether an intersection leg is an entrance leg or an exit leg depends on which movement is being analyzed. For two way roadways, each leg is an entrance leg for some movements and an exit leg for other movements. intersection sight distance The distance that the driver of a vehicle on the crossroad can see along the through roadway, as compared to the distance required for safe operation. island A defined area within an intersection, between traffic lanes, for the separation of vehicle movements or for pedestrian refuge. It may be outlined with pavement markings or delineated by curbs. Within an intersection, a median is considered an island. channelization island An island that separates traffic movements into definite paths of travel and guides traffic into the intended route. divisional island An island introduced, on an undivided roadway, at an intersection to warn drivers of the crossroad ahead and regulate traffic through the intersection. refuge island An island at or near a crosswalk or bicycle path to aid and protect pedestrians and bicyclists crossing the roadway. median crossover An opening in a median provided for crossings by maintenance, law enforcement, emergency,
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and traffic service vehicles. (See Chapter 960.) roundabout A circular intersection at which all traffic moves counterclockwise around a central island. (See Chapter 915) rural intersection An intersection in a nonurban area. Design Manual M 22-01 Intersections At Grade May 2006 Page 910-3 urban intersection An intersection that is in one of the following areas: • The area within the federal urban area boundary as designated by FHWA. • An area characterized by intensive use of the land for the location of structures and receiving such urban services as sewers, water, and other public utilities and services normally associated with urbanized areas. • An area with not more than 25% undeveloped land. ## 910.04 Design Considerations Intersection design requires consideration of all potential users of the facility. This involves addressing the needs of a diverse mix of user groups including passenger cars, heavy vehicles of varying classifications, bicycles, and pedestrians. Often, meeting the needs of one user group requires a compromise in service to others. Intersection design balances these competing needs, resulting in appropriate levels of operation for all users. In addition to reducing the number of conflicts, minimize the conflict area as much as possible while still providing for the required design vehicle (910.05). This is done to control the speed of turning vehicles and reduce vehicle, bicyclist, and pedestrian exposure. (1) Traffic Analysis Conduct a traffic analysis and an accident analysis to determine the design characteristics of each intersection. Include recommendations for channelization, turn lanes, acceleration and deceleration lanes, intersection configurations, illumination, bicycle and pedestrian accommodations, ADA requirements, and traffic control devices in the traffic analysis. (2) Intersection Configurations (a) Intersection angle. An important intersection design characteristic is the intersection angle. The desirable intersection angle is 90°, with 75° to 105° allowed for new, reconstructed, or realigned intersections.
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Existing intersections with an intersection angle between 60° and 120° may remain. Intersection angles outside this range tend to restrict visibility, increase the area required for turning, increase the difficulty to make a turn, increase the crossing distance and time for vehicles and pedestrians, and make traffic signal arms difficult or impossible to design. (b) Lane alignment. Design intersections with entrance lanes aligned with the exit lanes. Do not put angle points on the roadway alignments within intersection areas or on the through roadway alignment within 100 f ee t of the edge of traveled way of a crossroad. This includes short radius curves where both the PC and PT are within the intersection area. However, angle points within the intersection are allowed at intersections with a minor through movement, such as at a ramp terminal (Figure 910-18). When practical, locate intersections so that curves do not begin or end within the intersection area. It is desirable to locate the PC and PT at least 250 fee t from the intersection so that a driver can settle into the curve before the gap in the striping for the intersection area. (c) Split Tee. Avoid split tee intersections where there is less than the required intersection spacing. see 910.04(4). Split tee intersections with an offset distance to the left greater than the width of the roadway, but less than the intersection spacing, may be designed with justification. Evaluate the anticipated benefits against the increased difficulty in driving through the intersection and a more complicated traffic signal design. Split tee intersections with the offset to the right have the additional disadvantages of overlapping main line left-turn lanes, increased possibility of wrong way movements, and traffic signal design that is even more complicated. Do not design a split tee intersection with an offset
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to the right less than the required intersection spacing [see 910.04(4)] unless traffic is restricted to right-in right-out only. Intersections At Grade Design Manual M 22-01 Page 910-4 May 2006 (d) Other Nonstandard Configurations. Do not design intersections with nonstandard configurations such as: • Intersections with offset legs, except for split tee intersections [910.04(2)(c)]. • Intersections with more than four legs. • Tee intersections with the major traffic movement making a turn. • Wye intersections that are not a one-way merge or diverge. A roundabout might be an alternative to these nonstandard configurations. (See 910.08 and Chapter 915.) With justification and approval from the region’s Traffic Engineer existing intersections with nonstandard configurations may remain in place when an analysis shows no accident history related to the configuration. (3) Crossroads When the crossroad is a city street or county road, design the crossroad beyond the intersection area according to the applicable design criteria given in Chapter 440 for a city street or county road. When the crossroad is a state facility, design the crossroad according to the applicable design level and functional class (Chapters 325, 430, and 440). Continue the cross slope of the through roadway shoulder as the grade for the crossroad. Use a vertical curve that is at least 60 f ee t long to connect to the grade of the crossroad. Consider the profile of the crossroad in the intersection area. To prevent operational problems, the crown slope of the main line might need to be adjusted in the intersection area. In areas that experience accumulations of snow and ice and for all legs that will require traffic to stop, design a maximum grade of ±4 % for a length equal to the anticipated queue length for stopped vehicles. (4) Intersection Spacing Adequate intersection spacing is required to
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provide for safety and the desired operational characteristics for the highway. The minimum spacing for highways with limited access control is covered in Chapter 1430. For other highways, the minimum spacing is dependent on the Highway Access Management Class. See Chapter 1435 for minimum intersection spacing on Managed Access highways. As a minimum, provide enough space between intersections for left-turn lanes and storage length. Space signalized intersections, and intersections expected to be signalized, to maintain efficient signal operation. It is desirable to space intersections so that queues will not block an adjacent intersection. ## 910.05 Design Vehicle The physical characteristics of the design vehicle control the geometric design of the intersection. The following design vehicle types are commonly used: > Design Symbol Vehicle Type > PPassenger car, including light delivery trucks. BUS Single unit bus A-BUS Articulated bus SU Single unit truck WB-40 Semitrailer truck, overall wheelbase of 40 ft WB-50 Semitrailer truck, overall wheelbase of 50 ft WB-67 Semitrailer truck, overall wheelbase of 67 ft MH Motor home P/T Passenger car pulling a camper trailer MH/B Motor home pulling a boat trailer Design Vehicle Types > Figure 910-2 Design Manual M 22-01 Intersections At Grade May 2006 Page 910-5 The geometric design of an intersection requires identifying and addressing the needs of all intersection users. There are competing design objectives when considering the turning requirements of the larger design vehicles and the crossing requirements of pedestrians. To reduce the operational impacts of large design vehicles, larger turn radii are used. This results in increased pavement areas, longer pedestrian crossing distances, and longer traffic signal arms. To reduce the intersection area, a smaller design vehicle is used or encroachment is allowed. This reduces the potential for vehicle/pedestrian conflicts, decreases pedestrian crossing distance, and controls speeds of turning vehicles. The negative
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impacts include possible capacity reductions and greater speed differences between turning vehicles and through vehicles. Select a design vehicle that is the largest vehicle that normally uses the intersection. The primary use of the design vehicle is to determine radii requirements for each leg of the intersection. It is possible for each leg to have a different design vehicle. Figure 910-3 shows the minimum design vehicles. As justification to use a smaller vehicle, include a traffic analysis showing that the proposed vehicle is appropriate. > Intersection Type Design Vehicle > Junction of Major Truck Routes WB-67 Junction of State Routes WB-50 Ramp Terminals WB-50 Other Rural WB-50 Industrial WB-40 Commercial SU(1)(2) Residential SU(1)(2) (1) To accommodate pedestrians, the P vehicle may be used as the design vehicle if > justification, with a traffic analysis, is > documented. (2) When the intersection is on a transit or school bus route, use the BUS design vehicle as a minimum. See Chapter 1060 for additional guidance for transit facilities. Intersection Design Vehicle > Figure 910-3 To minimize the disruption to other traffic, design the intersection to allow the design vehicles to make each turning movement without encroaching on curbs, opposing lanes, or same-direction lanes at the entrance leg. Use turning path templates (Figures 910-6a through 6c, templates from another published source, or computer generated templates) to verify that the design vehicle can make the turning movements. Encroachment on same-direction lanes of the exit leg and the shoulder might be necessary to minimize crosswalk distances; however, this might negatively impact vehicular operations. Document and justify the operational tradeoffs associated with this encroachment. When encroachment on the shoulder is required, increase the pavement structure to support the anticipated traffic. In addition to the design vehicle, often a larger vehicle must be considered. When vehicles larger
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than the design vehicle are allowed and are anticipated to occasionally use the intersection make certain that they can make the turn without leaving the paved shoulders or encroaching on a sidewalk. The amount of encroachment allowed is dependent on the frequency of the vehicle and the resulting disruption to other traffic. Use the WB-67 as the largest vehicle at all state route to state route junctions. Document and justify any required encroachment into other lanes, and any degradation of intersection operation. ## 910.06 Right-Turn Corners The geometric design of an intersection requires identifying and addressing the needs of all intersection users. For the design of right-turn corners, there can be competing design objectives when considering the turning requirements of the design vehicle and the crossing requirements of pedestrians. To reduce the operational impacts of large trucks, right-turn radii are designed so that the truck can complete its turn without encroaching on the adjacent lanes at either the entrance or the exit legs of the turn. This results in larger corner radii, increased pavement area and pedestrian crossing distance, a larger conflict area, and higher vehicle turning speeds. Intersections At Grade Design Manual M 22-01 Page 910-6 May 2006 When pedestrian issues are a primary concern, the design objectives become one of reducing the potential for vehicle/pedestrian conflicts. This is done by minimizing pedestrian crossing distance and controlling the speeds of turning vehicles. This normally leads to right-corner designs with smaller turning radii. The negative impacts include possible capacity reductions and greater speed differences between turning vehicles and through vehicles. Pedestrian refuge islands can also improve pedestrian safety. Pedestrian refuge islands minimize the crossing distance, reduce the conflict area, and minimize the impacts on vehicular traffic. When designing islands, speeds can be reduced by designing the turning roadway with a
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taper or large radius curve at the beginning of the turn and a small radius curve at the end. This allows larger islands while forcing the turning traffic to slow down. Figure 910-7 shows right-turn corner designs for the design vehicles. These are considered the minimum pavement area to accommodate the design vehicles without encroachment on the adjacent lane at either leg of the curve. With justification, right-turn corner designs given in Figure 910-7 may be modified. Document the benefits and impacts of the modified design including: changes to vehicle pedestrian conflicts, vehicle encroachment on the shoulder or adjacent same direction lane at the exit leg, capacity restrictions for right-turning vehicles or other degradation of intersection operations, and the effects on other traffic movements. To verify that the design vehicle can make the turn, include a plot of the design showing the design vehicle turning path template. ## 910.07 Channelization Channelization is the separation or regulation of traffic movements into delineated paths of travel to facilitate the safe and orderly movement of vehicles, bicycles, and pedestrians. Painted or plastic pavement markings are normally used to delineate travel paths. (See Chapter 830 and the standard Plans for details.) (1) Left-Turn Lanes Left-turn lanes provide storage, separate from the through lanes, for left-turning vehicles waiting for a signal to change or for a gap in opposing traffic. (See 910.07(3) for a discussion on speed change lanes.) Design left-turn channelization to provide sufficient operational flexibility to function under peak loads and adverse conditions. (a) One-Way Left-Turn Lanes are separate storage lanes for vehicles turning left from one roadway onto another. When recommended, one-way left-turn lanes may be an economical way to lessen delays and accident potential involving left-turning vehicles. In addition, they can allow deceleration clear of the through traffic lanes. When considering
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left-turn lanes, consider impacts to all intersection movements and users. At signalized intersections, use a traffic signal analysis to determine if a left-turn lane is needed and what the storage requirements are. (See Chapter 850.) At unsignalized intersections, use the following as a guide to determine whether or not to provide one-way left-turn lanes: • A traffic analysis indicates that a left-turn lane will reduce congestion. On two-lane highways, use Figure 910-8a, based on total traffic volume (DHV) for both directions and percent left-turn traffic, to determine if further investigation is needed. On four-lane highways, use Figure 910-8b to determine if a left-turn lane is recommended. • An accident study indicates that a left-turn lane will reduce accidents. • Restrictive geometrics require left-turning vehicles to slow greatly below the speed of the through traffic. • There is less than decision sight distance at the approach to the intersection. An HCM analysis may also be used to determine if left-turn lanes are necessary to maintain the desired level of service. Design Manual M 22-01 Intersections At Grade May 2006 Page 910-7 Determine the storage length required on two-lane highways by using Figures 910-9a through 9c. On four-lane highways use Figure 910-8b. These lengths do not consider trucks. Use Figure 910-4 for storage length when trucks are present. > Storage* Length (ft) % Trucks in Left-Turn Movement 10 20 30 40 50 100 125 125 150 150 150 150 175 200 200 200 200 200 225 250 275 300 300 250 275 300 325 350 375 300 350 375 400 400 400 *Length from Figures 910-8b, 9a, 9b, or 9c. Left-Turn Storage With Trucks (ft) > Figure 910-4 Design opposing left-turn design vehicle paths with a minimum 4-foot (12-foot desirable) clearance between opposing turning paths. Existing signalized intersections that do not meet
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the 4-foot clearance may remain with split signal phasing, an evaluate upgrade, and concurrence from the HQ Traffic Office. Where one-way left-turn channelization with curbing is to be provided, ensure that surface water will drain. Provide illumination at left-turn lanes in accordance with the guidelines in Chapter 840. At signalized intersections with high left-turn volumes, double left-turn lanes may be needed to maintain the desired level of service. A throat width of 30 to 36 f ee t is desirable on the exit leg of the turn to offset vehicle offtracking and the difficulty of two vehicles turning abreast. Use turning path templates to verify that the design vehicle can complete the turn. Where the design vehicle is a WB-40 or larger it is preferred to provide for the design vehicle and an SU turning abreast rather than two design vehicles turning abreast. Figures 910-10a through 10e show one-way left-turn geometrics. Figure 910-10a shows widening to accommodate the new lane. Figures 910-10c and 10d show the use of a median. Figure 910-10e shows the minimum protected left-turn with a median. 1. Widening (Figure 910-10a). It is desirable that offsets and pavement widening be symmetrical about the centerline or base line. Where right of way or topographic restrictions, crossroad alignments, or other circumstances preclude symmetrical widening, pavement widening may be on one side only. 2. Divided Highways (Figure 910-10b through 10d). Widening is not required for left-turn lane channelization where medians are 11 fee t wide or wider. For medians between 13 f ee t and 23 f ee t or where the acceleration lane is not provided, it is desirable to design the left-turn lane adjacent to the opposing lane, as shown on Figure 910-10b, to improve sight distance. A median acceleration lane, shown on Figures 910-10c and 10d, may
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be provided where the median is 23 f ee t or wider. The median acceleration lane might not be necessary at a signalized intersection. When a median acceleration lane is to be used, design it in accordance with 910.07(3) Speed Change Lanes. Where medians have sufficient width, provide a 2-foot shoulder adjacent to a left-turn lane. 3. Minimum Protected Left-Turn with a Median (Figure 910-10e). At intersections on divided highways where channelized left-turn lanes are not provided, consider the minimum protected storage area. With justification, left-turn lane designs given in Figures 910-10a through 10d may be modified. Document the benefits and impacts of the modified design including: changes to vehicle pedestrian conflicts, vehicle encroachment, deceleration length, capacity restrictions for turning vehicles or other degradation of intersection operations, and the effects on other traffic movements. The modified design must be able to accommodate the design vehicle and provide for the striping requirements of the Standard Plans and the MUTCD. To verify that the design vehicle can make the turn, include a plot of the design showing the design vehicle turning path template. Intersections At Grade Design Manual M 22-01 Page 910-8 May 2006 (b) Two-Way Left-Turn Lanes (TWLTL) are located between opposing lanes of traffic. They are used by vehicles making left turns from either direction, either from or onto the roadway. Use TWLTLs only on managed access highways where there are no more than two through lanes in each direction. Consider installation of TWLTLs where: • An accident study indicates that a TWLTL will reduce accidents. • There are existing closely spaced access points or minor street intersections. • There are unacceptable through traffic delays or capacity reductions because of left turning vehicles. A TWLTL can reduce delays to through traffic, reduce rear-end accidents, and provide separation between opposing lanes
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of traffic. However, they do not provide a safe refuge for pedestrians and can encourage strip development with additional closely spaced access points. Consider other alternatives, before using a TWLTL, such as prohibiting midblock left-turns and providing for U-turns. See Chapters 440 and 1435 for additional restrictions on the use of TWLTLs. The basic design for a TWLTL is illustrated on Figure 910-10f. Additional criteria are: • The desirable length of a TWLTL is not less than 250 f ee t. • Provide illumination in accordance with the guidelines in Chapter 840. • Pavement markings, signs, and other traffic control devices must be in accordance with the MUTCD and the Standard Plans. • Provide clear channelization when changing from TWLTL to one-way left-turn lanes at an intersection. (2) Right-Turn Lanes and Drop Lanes Right-turn movements influence intersection capacity even though there is no conflict between right-turning vehicles and opposing traffic. Right-turn lanes might be needed to maintain efficient intersection operation. Use the following as guidelines to determine when to consider right-turn lanes at unsignalized intersections: • Recommendation from Figure 910-11 based on same direction approach and right-turn traffic volumes for multilane roadways with a posted speed 45 miles per hour or above and for all two-lane roadways. • An accident study indicates that a right-turn lane will result in an overall accident reduction. • Presence of pedestrians who require right-turning vehicles to stop. • Restrictive geometrics that require right-turning vehicles to slow greatly below the speed of the through traffic. • Less than decision sight distance at the approach to the intersection. For unsignalized intersections, see 910.07(3) Speed Change Lanes for guidance on right-turn lane lengths. For signalized intersections, use a traffic signal analysis to determine if a right-turn lane is needed and the length requirement. (See Chapter 850.) A
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capacity analysis may be used to determine if right-turn lanes are necessary to maintain the desired level of service. Where adequate right of way exists, providing right-turn lanes is relatively inexpensive and can provide increased safety and operational efficiency. The right-turn pocket or the right-turn taper (Figure 910-12) may be used at any minor intersection where a deceleration lane is not required and turning volumes indicate a need as set forth in Figure 910-11. These designs will cause less interference and delay to the through movement by offering an earlier exit to right-turning vehicles. If the right-turn pocket is used, Figure 910-12 shows taper lengths for various posted speeds. A lane may be dropped at an intersection with a turn-only lane or beyond the intersection with an acceleration lane (Figure 910-14). Do not allow a lane-reduction taper to cross an intersection or end less than 100 f ee t before an intersection. Design Manual M 22-01 Intersections At Grade May 2006 Page 910-9 When a lane is dropped beyond a signalized intersection, provide a lane of sufficient length to allow smooth merging. For facilities with a posted speed of 45 miles per hour or higher, use a minimum length of 1,500 f ee t. For facilities with a posted speed less than 45 miles per hour, provide a lane of sufficient length so that the advanced lane reduction warning sign will be placed not less than 100 f ee t beyond the intersection area. (3) Speed Change Lanes A speed change lane is an auxiliary lane primarily for the acceleration or deceleration of vehicles entering or leaving the through traveled way. Speed change lanes are normally provided for at-grade intersections on multilane divided highways with access control. Where roadside conditions and right of way allow, speed change lanes may be
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provided on other through roadways. Justification for a speed change lane depends on many factors such as speed, traffic volumes, capacity, type of highway, the design and frequency of intersections, and accident history. A deceleration lane is advantageous because, if a deceleration lane is not provided the driver leaving the highway must slow down in the through lane regardless of following traffic. An acceleration lane is not as advantageous because entering drivers can wait for an opportunity to merge without disrupting through traffic. When either deceleration or acceleration lanes are to be used, design them in accordance with Figures 910-13 and 14. When the design speed of the turning traffic is greater than 20 miles per hour, design the speed change lane as a ramp in accordance with Chapter 940. When a deceleration lane is used with a left-turn lane, add the deceleration length to the storage length. (4) Shoulders With justification, shoulder width requirements may be reduced within areas channelized for intersection turning lanes or speed change lanes. Apply left shoulder width criteria to the median shoulder of divided highways. On one-way couplets, apply the width criteria for the right shoulder to both the right and left shoulders. For roadways without curb sections, the shoulder adjacent to turn lanes and speed change lanes may be reduced to 2 f ee t on the left and 4 f ee t on the right. When a curb and sidewalk section is used with a turn lane or speed change lane, 400 f ee tor less in length, the shoulder abutting the turn lane may be eliminated. In instances where curb is used without sidewalk, provide a minimum of 4 foot wide shoulders on the right. Where curbing is used adjacent to left turn lanes, the shoulder may be eliminated. Adjust the
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design of the intersection as necessary to allow for vehicle tracking. Reducing the shoulder width at intersections facilitates the installation of turn lanes without unduly affecting the overall width of the roadway. A narrower roadway also reduces pedestrian exposure in crosswalks and discourages motorists from using the shoulder to bypass other turning traffic. On routes where provisions are made for bicycles, continue the bicycle facility between the turn lane and the through lane. (See Chapter 1020 for information on bicycle facilities.) (5) Islands An island is a defined area within an intersection between traffic lanes for the separation of vehicle movements or for pedestrian refuge. Within an intersection, a median is considered an island. Design islands to clearly delineate the traffic channels to drivers and pedestrians. Traffic islands perform these functions: • Channelization islands control and direct traffic movement. • Divisional islands separate traffic movements. • Refuge islands provide refuge for pedestrians. • Islands can provide for the placement of traffic control devices and luminaires. • Islands can provide areas within the roadway for landscaping. (a) Size and Shape. Divisional and refuge islands are normally elongated and at least 4 f ee twide and 20 f ee t long. (Mountable curb, used to discourage turn movements, is not a divisional island.) Intersections At Grade Design Manual M 22-01 Page 910-10 May 2006 Channelization islands are normally triangular. In rural areas, 75 ft 2 is the minimum island area and 100 ft 2 is desirable. In urban areas where posted speeds are 25 miles per hour or less, smaller islands are acceptable. Use islands with at least 200 ft 2 if pedestrians will be crossing or traffic control devices or luminaires will be installed. Design triangular shaped islands as shown on Figure 910-15a through 15c. The shoulder and offset widths illustrated
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are for islands with vertical curbs 6 inches or higher. Where painted islands are used, such as in rural areas, these widths are desirable but may be omitted. See Chapter 641 for turning roadway widths. Island markings may be supplemented with reflective raised pavement markers. Barrier-free access must be provided at crosswalk locations where raised islands are used. See Chapter 1025. (b) Location. Design the approach ends of islands to provide adequate visibility to alert the motorist of their presence. Position the island so that a smooth transition in vehicle speed and direction is attained. Begin transverse lane shifts far enough in advance of the intersection to allow gradual transitions. Avoid introducing islands on a horizontal or vertical curve. If the use of an island on a curve cannot be avoided, provide adequate sight distance, illumination, or extension of the island. (c) Compound Right-Turn Lane. To design large islands, the common method is to use a large radius curve for the turning traffic. While this does provide a larger island, it also encourages higher turning speeds. Where pedestrians are a concern, higher turning speeds are undesirable. An alternative is a compound curve with a large radius followed by a small radius (Figure 910-15b). This design forces the turning traffic to slow down. (d) Curbing. Provide vertical curb 6 inches or higher for: • Islands with luminaires, signals, or other traffic control devices. • Pedestrian refuge islands. In addition consider curbing for: • Divisional and channelizing islands. • Landscaped islands. In general, unless required for the uses listed above, it is preferred not to use curbs on facilities with a posted speed of 45 miles per hour or greater. Avoid using curbs if the same objective can be attained with pavement markings. See Chapter 440 for additional information and requirements on
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the use of curbs. ## 910.08 Roundabouts Modern roundabouts are circular intersections. They can be an effective intersection type. Modern roundabouts differ from the old rotaries and traffic circles in two important respects: they have a smaller diameter, which lowers speeds; and they have splitter islands that provide entry constraints, slowing down the entering speeds. When well designed, roundabouts are an efficient form of intersection control. They have fewer conflict points, lower speeds, easier decision making, and they require less maintenance. When properly designed and located, they have been found to reduce injury accidents, traffic delays, fuel consumption, and air pollution. Roundabouts also permit U-turns. Consider roundabouts at intersections with the following characteristics: • Where stop signs result in unacceptable delays for the cross road traffic. Roundabouts reduce the delays for the cross road, but increase the delays for the through roadway. • With a high left-turn percentage. Unlike most intersection types, roundabouts can operate efficiently with high volumes of left-turning traffic. • With more than four legs. When the intersection cannot be modified by closing or relocating legs, a roundabout can provide a solution. • Where a disproportionately high number of accidents involve crossing or turning traffic. • Where the major traffic movement makes a turn. Design Manual M 22-01 Intersections At Grade May 2006 Page 910-11 • Where traffic growth is expected to be high and future traffic patterns are uncertain. • Where it is not desirable to give priority to either roadway. There are some disadvantages with roundabouts. Roundabouts do not allow for a primary roadway to have priority because all legs entering a roundabout are treated the same. Also, all traffic entering a roundabout is required to reduce speed. Therefore, roundabouts are not appropriate on high speed facilities, where traffic flows are unbalanced, or where an
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arterial intersects a collector or local road. See Chapter 915 for information and requirements on the design of roundabouts. ## 910.09 U-Turns For divided highways without full access control that have access points where a median prevents left turns, consider providing locations designed to allow U-turns. Normally, the U-turn opportunities are provided at intersections; however, where intersections are spaced far apart, consider median openings between intersections to accommodate U-turns. Use the desirable U-turn spacing (Figure 910-5) as a guide to determine when to consider U-turn locations between intersections. When the U-turning volumes are low, use longer spacing. > U-Turn Spacing Desirable Minimum > Urban (1) 1,000 ft (2) Suburban 1/2mi 1/4mi (3) Rural 1 mi 1/2mi (1) For design speeds greater than 45 mph use suburban spacing. (2) The minimum spacing is the acceleration lane length from a stop (Figure 910-14) plus 300 feet (3) For design speeds 60 mph or greater, the minimum spacing is the acceleration lane length from a stop (Figure 910-14) plus 300 feet U-Turn Spacing > Figure 910-5 When designing U-turn locations, use Figure 910-16 as a guide. Where the median is less than 40 f ee t wide and a large design vehicle is required, consider the use of a U-turn roadway (jug handle). Document the need for U-turn locations, the spacing used, and justify the selected design vehicle. U-turns at signal controlled intersections do not require the acceleration lanes shown in Figure 910-16. At new U-turn locations at signal controlled intersections, ensure that right-turning vehicles from side streets will not conflict with U-turning vehicles. Warning signs on the cross street might be appropriate. ## 910.10 Sight Distance at Intersections For traffic to move safely through intersections, drivers need to be able to see stop signs, traffic signals, and oncoming traffic in time to
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react accordingly. Provide decision sight distance, where practical, in advance of stop signs, traffic signals, and roundabouts. See Chapter 650 for guidance. The driver of a vehicle that is stopped, waiting to cross or enter a through roadway, needs obstruction-free sight triangles in order to see enough of the through roadway to safely complete all legal maneuvers before an approaching vehicle on the through roadway can reach the intersection. Use Figure 910-17a to determine minimum sight distance along the through roadway. The sight triangle is determined as shown in Figure 910-17b. Within the sight triangle, lay back the cut slopes and remove, lower, or move hedges, trees, signs, utility poles, and anything else large enough to be a sight obstruction. Consider eliminating parking so sight distance is not obstructed. In order to maintain the sight distance, the sight triangle must be within the right of way or a state maintenance easement (see Chapter 1410). Intersections At Grade Design Manual M 22-01 Page 910-12 May 2006 The minimum setback distance for the sight triangle is 18 f ee t from the edge of traveled way. This is for a vehicle stopped 10 f ee t from the edge of traveled way. The driver is almost always 8 f ee tor less from the front of the vehicle; therefore, 8 fee t is added to the setback. When the stop bar is placed more than 10 f ee t from the edge of traveled way, consider providing the sight triangle to a point 8 f ee t back of the stop bar. Provide a clear sight triangle for a P vehicle at all intersections. In addition to this, provide a clear sight triangle for the SU vehicle for rural highway conditions. If there is significant combination truck traffic, use the WB-50 or
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WB-67 rather than the SU. In areas where SU or WB vehicles are minimal, and right of way restrictions prohibit adequate sight triangle clearing, only the P vehicle need be considered. At existing intersections, when sight obstructions within the sight triangle cannot be removed due to limited right of way, the intersection sight distance may be modified. A driver that does not have the desired sight distance will creep out until the sight distance is available; therefore, the 10 -foot stopping distance from the edge of traveled way may be reduced to 2-foot, reducing the setback to 10 f ee t. Also, the time gap (t g) may be reduced by the 2-sec ond perception/reaction time. Document the right of way width and provide a brief analysis of the intersection sight distance clarifying the reasons for reduction. Verify and document that there is not an accident problem at the intersection. Document as a design exception. If the intersection sight distance cannot be provided using the reductions in the preceding paragraph, the calculated sight distance may be reduced, with HQ Design Office approval. Provide as much sight distance as practical, but not less than the stopping sight distance required for the major roadway, with visibility at the 10 -foot setback point. (For required stopping sight distance, see Chapter 650.) Document the right of way width and provide a brief analysis of the intersection sight distance clarifying the reasons for reduction. Verify and document that there is not an accident problem at the intersection. Document as a design exception. In some instances intersection sight distance is provided at the time of construction, but subsequent vegetative growth has degraded the sight distance available. The growth may be seasonal or occur over time. In these instances, the intersection sight distance will be restored through
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periodic scheduled maintenance of vegetation in the sight triangle within the WSDOT right of way or state maintenance easement. At intersections controlled by traffic signals, provide sight distance for right-turning vehicles. Designs for movements that cross divided highways are influenced by the median widths. If the median is wide enough to store the design vehicle, with 3 f ee t clearance at both ends of the vehicle, sight distances are determined in two steps. The first step is for crossing from a stopped position to the median storage; the second step is for the movement, either across, or left into the through roadway. Design ramp terminal sight distance as at-grade intersections considering only left- and right- turning movements. An added element at ramp terminals is the grade separation structure. Figure 910-17b gives the sight distance considerations in the vicinity of a structure. In addition, when the crossroad is an undercrossing, check the sight distance under the structure graphically using a truck eye height of 6 f ee t and an object height of 1.5 f ee t. Document a brief description of the intersection area, sight distance restrictions, and traffic characteristics to support the design vehicle and sight distances chosen. ## 910.11 Traffic Control at Intersections Intersection traffic control is the process of moving traffic safely through areas of potential conflict where two or more roadways meet. Signs, signals, channelization, and physical layout are the major tools used to establish intersection control. There are three objectives to intersection traffic control that can greatly improve intersection operations. Design Manual M 22-01 Intersections At Grade May 2006 Page 910-13 • Maximize Intersection Capacity. Since two or more traffic streams cross, converge, or diverge at intersections, capacity of an intersection is normally less than the roadway between intersections. It is usually necessary to
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assign right of way through the use of traffic control devices to maximize capacity for all users of the intersection. Turn prohibitions may be used to increase intersection capacity. • Reduce Conflict Points. The crossing, converging, and diverging of traffic creates conflicts which increase the potential for accidents. Establishing appropriate controls can reduce the possibility of two cars attempting to occupy the same space at the same time. Pedestrian accident potential can also be reduced by appropriate controls. • Priority of Major Streets. Traffic on major routes is normally given the right of way over traffic on minor streets to increase intersection operational efficiency. If a signal is being considered or exists at an intersection that is to be modified, a preliminary signal plan is required (Chapter 850). If a new signal permit is required, it must be approved before the design is approved. A proposal to install a traffic signal or a roundabout on a state route, either NHS or Non-NHS, with a posted speed limit of 45 miles per hour or higher requires an analysis of alternatives, approved by the region’s Traffic Engineer with review and comment by the Headquarters Design Office, prior to proceeding with the design. Include the following alternatives in the analysis: • Channelization, providing deceleration lanes, storage, and acceleration lanes for left- and right-turning traffic. • Right-off /right-on with U-turn opportunities. • Grade separation. • Roundabouts. • Traffic control signals. Include a copy of the analysis with the preliminary signal plan or roundabout justification. ## 910.12 Interchange Ramp Terminals The design to be used or modified for use on one-way ramp terminals with stop or traffic signal control at the local road is shown on Figure 910-18. Higher volume intersections with multiple ramp lanes are designed individually. Due to probable development of large traffic
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generators adjacent to an interchange, width for a median on the local road is desirable whenever such development is believed imminent. This allows for future left-turn channelization. Use median channelization when justified by capacity determination and analysis, or by the need to provide a smooth traffic flow. Determine the number of lanes for each leg by capacity analysis methods assuming a traffic signal cycle, preferably 45 or 60 seconds in length, regardless of whether a signal is used or not. Consider all terminals in the analysis. Adjust the alignment of the intersection legs to fit the traffic movements and to discourage wrong way movements. Use the allowed intersecting angles of 75° to 105° (60° to 120° for modified design level) to avoid broken back or reverse curves in the ramp alignment. ## 910.13 Procedures Document design considerations and conclusions in accordance with Chapter 330. For highways with limited access control, see Chapter 1430 for requirements. (1) Approval An intersection is approved in accordance with Chapter 330. When required, the following items must be completed before an intersection may be approved: • Traffic analysis. • Deviations approved in accordance with Chapter 330. • Preliminary traffic signal plan approved by the HQ Traffic Office. (See Chapter 850.) • HQ Design Office approval for intersections with roundabouts. See Chapter 915 for approval procedures. Intersections At Grade Design Manual M 22-01 Page 910-14 May 2006 (2) Intersection Plans Intersection plans are required for any increases in capacity (turn lanes) of an intersection, modification of channelization, or change of intersection geometrics. Support the need for intersection or channelization modifications with history, school bus and mail route studies, hazardous materials route studies, pedestrian use, public meeting comments, and so forth. For information to be included on the Intersection Plan for Approval, see the Intersection/ Channelization Plan
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for Approval Check List on the following web site: > default.htm (3) Local Agency or Developer Initiated Intersections There is a separate procedure for local agency or developer-initiated projects at intersections with state routes. The project initiator submits an intersection plan, and the documentation of design considerations that led to the plan, to the region for approval. For those plans requiring a deviation, the deviation must be approved in accordance with Chapter 330 prior to approval of the plan. After the plan approval, the region prepares a construction agreement with the project initiator. (See the Utilities Manual .) ## 910.14 Documentation The list of documents that are to be preserved in the Design Documentation Package (DDP) or the Project File (PF) is on the following web site: > Design Manual M 22-01 Intersections At Grade May 2006 Page 910-25 Median Channelization (Median Width 11 ft or more) Figure 910-10b Notes: (1) Lane width of 13 ft is desirable. (2) For left-turn storage length, see Figures 910-8b for 4-lane roadways or 9a through 9c for 2-lane roadways. (3) Desirable radius not less than 50 ft. Use templates to verify that the design vehicle can make the turn. (4) See Figure 910-7 for right-turn corner design. (5) For median widths greater than 13 ft, it is desirable to locate the left-turn lane adjacent to the opposing through lane with excess median width between the same direction through lane and the turn lane. (6) For increased storage capacity, consider the left-turn deceleration taper alternate design. (7) Reduce to lane width for medians less that 13 ft wide. (8) See Standard Plans and MUTCD for pavement marking details. Intersections At Grade Design Manual M 22-01 Page 910-26 May 2006 Notes: (1) Lane widths of 13 ft are desirable for both the left-turn
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storage lane and the median acceleration lane. (2) For left-turn storage length, see Figures 910-8b for 4-lane roadways or 9a throug9c for 2-lane roadways. (3) Desirable radius not less than 50 ft. Use templates to verify that the design vehicle can make the turn. (4) See Figure 910-7 for right-turn corner design. (5) The minimum total length of the median acceleration lane is shown in Figure 910-14. (6) See Table 2, for acceleration taper rate. (7) For increased storage capacity, consider the left-turn deceleration taper alternate design. (8) See Standard Plans and MUTCD for pavement marking details. Posted Speed Taper Rate 55 mph 55:1 50 mph 50:1 45 mph 45:1 40 mph 27:1 35 mph 21:1 30 mph 15:1 25 mph 11:1 Table 2 Median Channelization (Median Width 23 ft to 26 ft) Figure 910-10c Design Manual M 22-01 Intersections At Grade May 2006 Page 910-27 Median Channelization (Median Width of More Than 26 ft) Figure 910-10d Notes: (1) May be reduced to 11 ft, with justification. (2) For left-turn storage length, see Figures 910-8b for 4-lane roadways or 9a through 9c for 2-lane roadways. (3) Desirable radius not less than 50 ft. Use templates to verify that the design vehicle can make the turn. (4) See Figure 910-7 for right-turn corner design. (5) The minimum length of the median acceleration lane is shown in Figure 910-14. (6) See Table 2 Figure 910-10c for acceleration taper rate. (7) See Standard Plans and MUTCD for pavement marking details. Intersections At Grade Design Manual M 22-01 Page 910-28 May 2006 Notes: Notes: (1) Desirable radius not less than 50 ft. Use templates to verify that the design vehicle can make the turn. (2) See Figure 910-7 for right-turn corner design. (3) For median width 17 ft or more. For median width less
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than 17 ft, widen to 17 ft or use Figure 910-10b. (4) See Standard Plans and MUTCD for pavement marking details. Median Channelization (Minimum Protected Storage) Figure 910-10e Design Manual M 22-01 Intersections At Grade January 2005 Page 910-37 U-Turn Locations > Figure 910-16 ChapterF9104.doc WSDOT Design Manual Intersections At Grade Draft September 1, 2004 Page 910-39 Vehicle W R L F1 F2 TP 52 14 14 12 12 SU 87 30 20 13 15 10:1 BUS 87 28 23 14 18 10:1 WB-40 84 25 27 15 20 6:1 WB-50 94 26 31 16 25 6:1 WB-67 94 22 49 15 35 6:1 MH 84 27 20 15 16 10:1 P/T 52 11 13 12 18 6:1 MH/B 103 36 22 15 16 10:1 U-Turn Design Dimensions Notes: (1) The minimum length of the acceleration lane is shown in Figure 910-14. Acceleration lane may be eliminated at signal controlled intersections. (2) All dimensions in feet. (3) When U-turn uses the shoulder, provide 12.5 ft shoulder width and shoulder pavement designed to the same depth as the through lanes for the acceleration length and taper. U-Turn Locations Figure 910-16 Vehicle W R L F1 F2 TP 52 14 14 12 12 —SU 87 30 20 13 15 10:1 BUS 87 28 23 14 18 10:1 WB-40 84 25 27 15 20 6:1 WB-50 94 26 31 16 25 6:1 WB-67 94 22 49 15 35 6:1 MH 84 27 20 15 16 10:1 P/T 52 11 13 12 18 6:1 MH/B 103 36 22 15 16 10:1 U-Turn Design Dimensions Notes: (1) The minimum length of the acceleration lane is shown in Figure 910-14. Acceleration lane may be eliminated at signal controlled intersections. (2) All dimensions in feet. (3) When U-turn uses the shoulder, provide 12.5 ft shoulder width and
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{
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shoulder pavement designed to the same depth as the through lanes for the acceleration length and taper. Intersections At Grade Design Manual M 22-01 Page 910-38 May 2006 Design Manual for Design-Build Projects Intersections At Grade November 2004 Page 910-41 SiLine of Sight SiLine of Sight VVgi 1.47Vt S Where: Si = Intersection Sight Distance (ft) V = Design speed of the through roadway (mph) t g = Time gap for the minor roadway traffic to enter or cross the through roadway (s) Intersection Sight Distance Equation Table 1 Design Vehicle Time Gap (t g)in seconds Passenger car (P) 9.5 Single unit trucks and buses (SU & BUS) 11.5 Combination trucks (WB-40, WB-50, & WB-67 ) 13.5 Note: Values are for a stopped vehicle to turn left onto a two-lane two-way roadway with no median and grades 3% or less. Includes 2 sec for perception/reaction time. Intersection Sight Distance Gap Times (t g) Table 2 The t g values listed in Table 2 require the following adjustments: Crossing or right-turn maneuvers: All vehicles subtract 1.0 s Multilane roadways: Left-turns, for each lane in excess of one to be crossed and for medians wider than 4 ft: Passenger cars add 0.5 s All trucks and buses add 0.7 s Crossing maneuvers, for each lane in excess of two to be crossed and for medians wider than 4 ft: Passenger cars add 0.5 s All trucks and buses add 0.7 s Note: Where medians are wide enough to store the design vehicle, determine the sight distance as two maneuvers. Crossroad grade greater than 3%: All movements upgrade, for each percent that exceeds 3%: All vehicles add 0.2 s Sight Distance at Intersections > Figure 910-17a Sight Distance at Intersections > Figure 910-17a Si = 1.47Vt gWhere: Si = Intersection Sight Distance (ft)
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V = Design speed of the through roadway (mph) tg = Time gap for the minor roadway traffic to enter or cross the through roadway (sec) Intersection Sight Distance Equation Table 1 Design Vehicle Time Gap (t g )in sec Passenger car (P) 9.5 Single unit trucks and buses (SU & BUS) 11.5 Combination trucks (WB-40, WB-50, & WB-67) 13.5 > Note: Values are for a stopped vehicle to turn left onto a two-lane two-way roadway with no median and grades 3% or less. Includes 2 sec for perception/reaction time. Intersection Sight Distance Gap Times (t g) Table 2 > The t gvalues listed in Table 2 require the following adjustments: > Crossing or right-turn maneuvers: > All vehicles subtract 1.0 sec > Multilane roadways: > Left-turns, for each lane in excess of one to be crossed and for medians wider than 4 ft: Passenger cars add 0.5 sec All trucks and buses add 0.7 sec Crossing maneuvers, for each lane in excess of two to be crossed and for medians wider than 4 ft: Passenger cars add 0.5 sec All trucks and buses add 0.7 sec > Note: Where medians are wide enough to store the design vehicle, determine the sight distance as two maneuvers. > Crossroad grade greater than 3%: > All movements upgrade, for each percent that exceeds 3%: All vehicles add 0.2 sec Design Manual M 22-01 Median Crossovers May 2006 Page 960-1 # Chapter 960 Median Crossovers In areas where there are three or more miles between access points, providing an unobtrusive crossover can improve emergency service or improve efficiency for traffic service and maintenance forces. Where crossovers are justified and used for winter maintenance operations such as snow and ice removal, the recommended minimum distance from the ramp merge or diverge point should be
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{
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1,000 feet to accommodate future ramp improvements. This distance may be decreased to improve winter maintenance efficiency based on an operational analysis. Include an operational analysis in the Design Documentation Package. ## 960.03 Design Utilize the following design criteria for all median crossovers, while taking into consideration the intended vehicle usage. Some of the criteria below may not apply to crossovers intended primarily for law enforcement: • Adequate median width at the crossover location is required to allow the design vehicle to complete a U-turn maneuver without backing. Use of the shoulder area is allowed for the execution of the U-turn maneuver. The typical design vehicles for this determination are a passenger car and a single unit truck. • Consider the type of vehicles using the median crossover. • The minimum recommended throat width is 30 feet. • Use grades and radii that are suitable for all authorized user vehicles. (See Chapter 920) • Ten-foot inside shoulders are adequate for most cases. Consider full ten-foot shoulders for a distance of 450 feet upstream of the crossover area to accommodate deceleration, and extend downstream of the crossover area for a distance of 600 feet to allow acceleration prior to entering the travel lane. Where inside shoulders can be constructed wide enough 960.01 General 960.02 Analysis 960.03 Design 960.04 Approval 960.05 Documentation ## 960.01 General This chapter provides guidance for locating and designing median crossovers. Median crossovers are provided at selected locations on divided highways for crossing by maintenance, traffic service, emergency, and law enforcement vehicles. The use of any median crossover is restricted to the users noted above. Crossovers may be provided: • Where analysis demonstrates that access through interchanges or intersections is not practical • As part of region maintenance operations • As necessary for law-enforcement functions For median openings
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