Question

In: Civil Engineering

Consider a 12 - mile segment of an existing four - lane freeway having very restricted...

Consider a 12 - mile segment of an existing four - lane freeway having very restricted geometry with rolling terrain. Peak hour volume is 2000 veh/h and the flow consist of 12% trucks and 3% recreational vehicles. The traffic is commuter type with peak hour factor 0.92. The freeway segment can be accessed by 6 on - ramps and has 8 off - ramps. Freeway consists of two lanes in each direction of 11 feet width with lateral clearance of 6 feet. Find the LOS of freeway during peak hour. (Assume basic free flow speed to be 70mi/hr)

Solutions

Expert Solution

Assume Base free flow speed (BFFS) = 70 mph

Lane width = 11 ft

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

Lateral Clearance = 6 ft

Reduction in speed corresponding to lateral clearance, fLC = 0 mph

Interchanges/Ramps = 14/12 miles = 1.17 /mile

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

No. of lanes in one direction = 2

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

Free Flow Speed (FFS) = BFFS – fLW – fLC – fN – fID= 70 – 1.9 – 0 – 4.5 – 2.5 = 61.1 mph

Peak Flow, V = 2000 veh/hr

Peak-hour factor = 0.92

Trucks = 12 %

RVs = 3 %

Rolling Terrain

fHV = 1/ (1 + 0.12 (2.5-1) + 0.03 (2.0-1)) = 1/1.21 = 0.826

fP = 1.0

Peak Flow Rate, Vp = V / (PHV*n*fHV*fP) = 2000/ (0.92*2*0.826*1.0) = 1315.93 ~ 1316 veh/hr/ln

Vp < 3400 - 30 FFS

S = FFS

S = 61.1 mph

Density = Vp/S = (1316) / (61.1) = 21.54 veh/mi/ln

Hence Level of Service is C

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

Ally Wells answered 2 years ago
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