An urban freeway is to be designed using the following information: AADT = 52,000 veh/day; K (proportion of AADT occurring during the peak hour) = 0.11; D (proportion of peak hour traffic traveling in the peak direction) = 0.65; trucks = 8% of peak hour volume; PHF = 0.95; lane width = 12 ft; shoulder width = 10 ft; total ramp density = 0.5 interchange/mile; all interchanges are to be cloverleaf interchanges; rolling terrain. Determine the number of lanes required to provide LOS C. Clearly state assumptions used for any values not given, and show all calculations required.

Question

What will be an ideal response?

Answer 1

Step 1: Compute directional design hourly volume (DDHV).

DDHV = (AADT)(K)(D) = (52000)(0.11)(0.65) = 3718 veh/h

Step 2: Compute passenger car equivalent flow rate for peak 15-minute period

using Equation 9.4

Assume 2 lanes in each direction will be sufficient.

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 4: Compute average passenger car speed and density to determine LOS.

For FFS = 69.64 mi/h, greater than 67.5 and less than 72.5, the 70 mi/h speedflow

curve will be used for this analysis. It was calculated that vp = 2191 pc/h/ln.



Using Figure 9.3a, this density corresponds to LOS E in the peak hour, so 2 lanes

are not enough.

Step 2: Try for 3 lanes



a) Compute average passenger car speed and density to determine LOS.

For FFS = 69.64 mi/h, greater than 67.5 and less than 72.5, the 70 mi/h speedflow

curve will be used for this analysis. It was calculated that vp = 1460 pc/h/ln.



Using Figure 9.3a, this density corresponds to LOS C, so 3 lanes are adequate.