Question

A six-lane freeway with three lanes in each direction is on a level terrain and has 11-ft

lanes with a 4-ft right-side shoulder. The total ramp density is 2 ramps per mile. The

directional peak-hour traffic volume is 5400 vehicles with a peak-hour factor of 0.95 and

all familiar users. The traffic stream includes 5% trucks and another 5% buses and no

recreational vehicles. The city has decided to ban all heavy vehicles from using the

freeway during the peak hour. Compute the level of service before and after the heavy

vehicle ban.

Answer 1

Assume Base free flow speed (BFFS) = 75 mph

Lane width = 11 ft

Reduction in speed corresponding to lane width, f_LW = 1.9 mph

Lateral Clearance = 4 ft

Reduction in speed corresponding to lateral clearance, f_LC = 0.8 mph

Interchanges/Ramps = 2 /mile

Reduction in speed corresponding to Interchanges/ramps, f_ID = 7.5 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 = 75 – 1.9 – 0.8 – 3 – 7.5 = 61.8 mph

Peak Flow, V = 5400 veh/hr

Peak-hour factor = 0.95

Trucks = 5 %

Buses = 5 %

RVs = 0 %

Level Terrain

f_HV = 1/ (1 + 0.05 (1.5-1) + 0.05 (1.5-1)) = 1/1.1 = 0.91

f_P = 1.0

a) LOS Before Heavy Vehicle Ban

Peak Flow Rate, V_p = V / (PHV*n*f_HV*f_P) = 5400/ (0.95*3*0.91*1.0) = 2082.13 ~ 2083 veh/hr/ln

(3400 – 30 FFS) < V_p < 2400

S = FFS – [1/9(7FFS-340) ((v_p + 30 FFS – 3400)/(40FFS-1700))^2.6]

S = 61.8 – [1/9(7 * 61.8-340) ((2083 + 30 * 61.8 – 3400)/ (40 * 61.8 -1700))^2.6]

S = 57.8 mph

Density = V_p/S = (2083) / (57.8) = 36.04 ~ 36 veh/mi/ln

Hence Level of Service is E

Density of LOS E should lie between 35 – 45 veh/mi/ln

b) LOS After Heavy Vehicle Ban

Peak Flow Rate, V_p = V / (PHV*n*f_HV*f_P) = 5400/ (0.95*3*1.0*1.0) = 1894.74 ~ 1895 veh/hr/ln

(3400 – 30 FFS) < V_p < 2400

S = FFS – [1/9(7FFS-340) ((v_p + 30 FFS – 3400)/(40FFS-1700))^2.6]

S = 61.8 – [1/9(7 * 61.8-340) ((1895 + 30 * 61.8 – 3400)/ (40 * 61.8 -1700))^2.6]

S = 60.5 mph

Density = V_p/S = (1895) / (60.5) = 31.32 ~ 31 veh/mi/ln

Hence Level of Service is D

Density of LOS D should lie between 26 – 35 veh/mi/ln