Question

An existing four lane section of urban freeway (3 lanes each way) is located in rolling terrain and has 10’ travel lanes, no lateral obstructions within 5’ of the pavement edge. The roadway has 8 ramps upstream and 4 ramps downstream of the midpoint of the six mile analysis segment. The traffic stream contains 10% trucks and buses, and 4% RV’s. The peak hour directional volume is 3200 vehicles with the heaviest 15 minute volume of 800 vehicles. What is the current level of service? f_p=0.95

Answer 1

Assume, Base free flow speed (BFFS) = 75 mph

Lane width = 10 ft

Reduction in speed corresponding to lane width, fLW = 6.6 mph

Lateral Clearance = 5 ft

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

Interchanges/Ramps = 12 /6 mile = 2/mile

Reduction in speed corresponding to Interchanges/ramps, fID = 7.5 mph

No. of lanes in each direction = 2

Reduction in speed corresponding to number of lanes, fN = 4.5 mph

Free Flow Speed (FFS) = BFFS – fLW – fLC – fN – fID = 75 – 6.6 – 0.6 – 4.5 – 7.5 = 55.8 mph

Peak hourly volume, V = 3200 veh/hr

Peak 15-min volume = 800 veh

Peak-hour factor = 3200/(4*800) = 1

Trucks & Buses = 10 %

RVs = 4 %

Rolling Terrain

fHV = 1/ (1 + 0.10 (2.5-1) + 0.04 (2.0-1)) = 1/1.19 = 0.84

fP = 0.95

Service Flow Rate, Vp = V / (fHV * PHF*n*fP) = 3200/ (0.84*1*2*0.95) = 2005 veh/hr/ln

Average Speed, S = FFS = 55.8 mph

Density = Vp/S = (2005) / (55.8) = 35.93 veh/mi/ln

LOS E

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