A freeway is to be designed to provide LOS C for the following conditions: design hourly volume of 5600 veh/h; PHF: 0.92; trucks: 6%; free flow speed: 70 mi/h; no lateral obstructions; rolling terrain; total ramp density of 0.75 ramps per mile. Determine: Number of 12 ft lanes required in each direction.

Question

What will be an ideal response?

Answer 1

Step 1: Compute heavy vehicle adjustment factor

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

Determine fHV (heavy vehicle adjustment factor), using Equation 9.5



Step 3: With field measurement of 70 mph, FFS = 70 mph.

Step 4: The expected speed of the traffic stream will be:

???? = 75 - 0.00001107 (????p - 1,000)2

???? = 75 - 0.00001107 (2205 - 1000)2

???? = 58.93 ????????/?



Using Figure 9.3a, this density corresponds to LOS E, therefore, a three lane

section is inadequate. Repeat steps 2 and 3.



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

For FFS = 72.87 mi/h, greater than 72.5 and less than 77.5, the 75 mi/h speedflow

curve will be used for this analysis. It was calculated that vp = 1654 pc/h/ln.



Using Figure 9.3a, this density corresponds to LOS C, therefore, a four lane

section is adequate.