Question

A section of a freeway on rolling terrain has the following properties: design hourly volume = 2500 vph, 10% trucks, 2% RVs, PHF = 0.95, two lanes 12 ft wide each, 5 ft lateral clearance and 8 ramps in every 10 miles. Determine the Level of Service (LOS) of the section according to the Highway Capacity Manual 2010.

Answer 1

Assume Base free flow speed (BFFS) = 70 mph

Lane width = 12 ft

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

Total Lateral Clearance = 5 ft

Reduction in speed corresponding to lateral clearance, f_LC = 0.6 mph

Total Ramp Density = 8/10 miles = 0.8 /mile

Reduction in speed corresponding to ramp density, f_{​​​​​ID} = 1.54 mph

Assume no. of lanes = 2

Reduction in speed corresponding to no. of lanes, f_N = 4.5 mph

Free Flow Speed (FFS) = BFFS – f_LW – f_LC – f_N – f_ID = 70 – 0 – 0.6 – 4.5 – 1.54 = 63.36 mph

Peak Flow, V = 2500 veh/hr

Peak-hour factor = 0.95

Trucks = 10%

RVs = 2%

Rolling Terrain

f_HV = 1/ (1 + 0.10 (2.5-1) + 0.02 (2.0 -1)) = 1/1.17 = 0.855

f_P = 1.0

Peak Flow Rate, V_p = V / (PHV*n*f_HV*f_P) = 2500/ (0.95 * 2 * 0.855 * 1.0) = 1538.94 ~ 1539 veh/hr/ln

S = FFS

Density = V_p/S = 1539/63.36 = 24.29 veh/mi/ln

Level of service C

Density of LOS C lies between 18 - 25 veh/mi/ln