Development of Accident Frequency Models with Random Parameters on Interstate Roadway Segments with and without Lighting Systems

Table 2

Recommendation for geometric standard design criteria.

Variables	Recommended standard values
Design speed	Urban freeways: 60 mph
	Rural freeways: 70 mph
Number of lanes	5 lanes in each direction
Right shoulder width	10 ft
	12 ft, where the DDHV for truck traffic exceeds 250 veh/h
Left (median) shoulder width	At least 4 ft
Grade
Urban & rural	3%, level terrain, 60 mph
Radius
Urban	1,090 ft, 60 mph
Rural	1,630 ft, 70 mph