Question

transportation design problem

1. A six-lane urban freeway is on level terrain with 12-ft lanes, obstructions 3-ft from the right edge of the traveled pavement, and nine ramps within three miles upstream and three miles downstream of the midpoint of the analysis segment. The traffic stream consists primarily of commuters. A directional weekday peak-hour volume of 2800 vehicles is observed with 900 vehicles arriving in the most congested 15-min period. If the traffic stream has 11% large trucks and buses and recreational vehicles, determine the level of service.

Answer 1

Assume Base free flow speed (BFFS) = 70 mph

Lane width = 12 ft

Reduction in speed corresponding to lane width, f_LW = 0.0 mph

Lateral Clearance = 3 ft

Reduction in speed corresponding to lateral clearance, f_LC = 1.2 mph

Interchanges/Ramps = 9 / 6 miles = 1.5 / mile

Reduction in speed corresponding to Interchanges/ramps, f_ID = 5 mph

No. of lanes = 3

Reduction in speed corresponding to number of lanes, f_N = 3 mph

Free Flow Speed (FFS) = BFFS – f_LW – f_LC – f_N – f_ID= 70 – 0.0 – 1.2 – 3 – 5 = 60.8 mph

Peak Flow, V = 2800 veh/hr

Peak 15-min = 900 veh

Peak-hour factor = 2800/(900*4) = 0.78

Trucks = 11 %

Level Terrain

f_HV = 1/ (1 + 0.11 (1.5-1)) = 1/1.055 = 0.95

f_P = 1.0

Peak Flow Rate, V_p = V / (PHV*n*f_HV*f_P) = 2800/ (0.78*3*0.95*1.0) = 1259.56 ~ 1260 veh/hr/ln

Vp < (3400 - 30 FFS)

S = FFS

S = 60.8 mph

Density = V_p/S = (1260) / (60.8) = 20.72 veh/mi/ln

Hence Level of Service is C

Density of LOS C should lie between 18 – 26 veh/mi/ln