An existing urban freeway with 4 lanes in each direction has the following characteristics: peak hour volume (in the peak direction) of 7070 veh/h, trucks are 10% of peak hour volume, PHF = 0.94, lane width = 11 ft, shoulder width = 6 ft, total ramp density = 1.8 ramps per mile, rolling terrain. Determine the LOS in the peak hour. Clearly state assumptions used for any values not given. Show the demand flow rate, mean speed, and density for the given conditions.
What will be an ideal response?
Step 1: Compute passenger car equivalent flow rate for peak 15-minute period
using Equation 9.4
Determine fp (driver population factor); assume mainly commuter traffic, fp = 1.0
Determine ET (PCE for trucks), using Table 9.3; ET = 2.5
Determine ER (PCE for RVs), using Table 9.3; ER = 2.0
PR = 0.00, as nothing is mentioned about recreational vehicles
Determine fHV (heavy vehicle adjustment factor), using Equation 9.5
Step 2: Compute free flow speed using Equation 9.2
FFS = 75.4 – fLW – fLC – 3.22TRD0.84
Determine fLW using Table 9.1, fLW = 1.9
Determine fLC using Table 9.2, fLC = 0.0
TRD = 1.8 ramps/mile
FFS = 75.4 – 1.9 – 0.0 – 3.22(1.8)0.84
FFS = 68.22 mi/h
Step 3: Compute average passenger car speed and density to determine LOS. For
FFS = 68.22 mi/h, greater than 67.5 and less than 72.5, the 70 mi/h speed-flow
curve will be used for this analysis. It was calculated that vp = 2163 pc/h/ln.
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