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45 TABLE B2 MINIMUM LANE AND SHOULDER WIDTHS RECOMMENDED IN TRB SR 214 10 Percent or More Trucksa Less Than 10 Percent Trucks Design Year Volume (ADT) Running Speed (mph) Lane Width (ft) Shoulder Widthb (ft) Lane Width (ft) Shoulder Width (ft) Under 50 10 2 9 2 1â750 50 & over 10 2 10 2 Under 50 11 2 10 2 751â2,000 50 & over 12 3 10 3 More than 2,000 All 12 6 11 6 a Trucks are defined as heavy vehicles with six or more tires. b One ft less for highways on mountainous terrain. (The table in that report has been revised to show shoulder width.) In SR 214, there are two columns labeled âCombined Lane and Shoulder Width.â In preparing Table B2, it is assumed that the shoulder width is the combined lane and shoulder width minus the lane width. No recommendation was made for multi-lane roads. Horizontal Curvature and Superelevation Recommendation 6: Highway agencies should increase the superelevation of horizontal curves when the design speed of an existing curve is below the running speeds (85th percentile) of approaching vehicles and the existing superelevation is below the allowable maximum specified by AASHTO new construction polices. Highway agencies should evaluate reconstruction of horizontal curves when the design speed of the existing curve is more than 15 mph below the running speeds of approaching vehicles (assuming improved superelevation cannot reduce the difference below the 15 mph) and the average daily traffic volume is greater than 750 vehicles per day. Recommendation 7: At horizontal curves where reconstruction is unwarranted, highway agencies should evaluate less costly safety measures. Vertical Curvature and Stopping Sight Distance Recommendation 8: Highway agencies should evaluate the reconstruction of hill crests when (a) the hill crest hides from view major hazards such as intersections, sharp horizontal curves, or narrow bridges; (b) the average daily traffic is greater than 1,500 vehicles per day; and (c) the design speed of the hill crest (based on the minimum stopping sight distance provided) is more than 20 mph below the running speeds (85th percentile) of the vehicles on the crest. Bridge Width Recommendation 9: Highway agencies should evaluate bridge replacement or widening if the bridge is less than 100 ft long and the usable width of the bridge is less than the following values: Design Year Volume (ADT) Usable Bridge Width (ft) 0â750 Width of approach lanes 751â2,000 Width of approach lanes plus 2 ft 2,001â4,000 Width of approach lanes plus 4 ft More than 4,000 Width of approach lanes plus 6 ft
46 Sideslopes and Clear Zones Recommendation 10: State highway agencies should develop consistent procedures for evaluating and improving roadside features with the following objectives: ⢠Flatten side slopes of 3:1 or steeper at locations where run-off-road accidents are likely to occur (e.g., on the outside of sharp horizontal curves); ⢠Retain current slope widths (without steepening side slopes) when widening lanes and shoulders unless warranted by special circumstances; and ⢠Remove, relocate, or shield isolated roadside obstacles. Pavement Edge Drop and Shoulder Type Recommendation 11: To reduce pavement edge-drop hazards on highways with narrow paved shoulders, highway agencies should either: ⢠Selectively pave shoulders at points where out-of-lane vehicle encroachments and pavement edge-drop problems are likely to develop (e.g., at horizontal curves); or ⢠Construct a beveled or tapered pavement edge shape at these points. Intersections Recommendation 12: State highway agencies should develop consistent procedures and checklists for evaluating intersection improvements on RRR projects. Normal Pavement Crown Recommendation 13: On resurfacing projects, highway agencies should construct pavement overlays with normal pavement crowns that match new construction standards.