Question

Determine Level of Service an urban freeway section, if the BFFS = 70 mph. The data are as follows:

Number of lanes: 4 (one direction)

Lane width = 12 ft.

Lateral clearance =5 ft. (right side)

Interchange density = 1 per mile

Percent trucks = 14

Percent RVs = 4

PHF = 0.95

Commuter traffic

Answer 1

Base free flow speed (BFFS) = 70 mph

Lane width = 12 ft

Reduction in speed corresponding to lane width, f_LW = 0 mph

Lateral Clearance = 5 ft

Reduction in speed corresponding to lateral clearance, f_LC = 0.2 mph

Interchanges/Ramps = 1 /mile

Reduction in speed corresponding to Interchanges/ramps, f_ID = 2.5 mph

No. of lanes = 4

Reduction in speed corresponding to number of lanes, f_N = 1.5 mph

Free Flow Speed (FFS) = BFFS – f_LW – f_LC – f_N – f_ID= 70 – 0 – 0.2 – 1.5 – 2.5 = 65.8 mph

Assume, flow = 3000 veh/hr

Peak-hour factor = 0.95

Trucks = 14 %

RVs = 4 %

Commuter Traffic

f_HV = 1/ (1 + 0.14 (1.5-1) + 0.04 (1.2-1)) = 1/1.078 = 0.928

f_P = 1.0

Peak Flow Rate, V_p = V / (PHV*n*f_HV*f_P) = 3000/ (0.95*4*0.928*1.0) = 850.73 ~ 851 veh/hr/ln

S = FFS = 65.8 mph

Density = V_p/S = 851 / 65.8 = 12.93 veh/mi/ln

Level of Service B

Density of LOS B should lies between 11 - 18 veh/mi/ln