Question

A freeway is being designed for a location in rolling terrain. The expected free-flow speed is 55 mi/h. During the peak hour, it is expected there will be a directional peak-hour volume of 2700 vehicles and 18% heavy vehicles. The PHF is expected to be 0.88. If a level of service no worse than D is desired, determine the necessary number of lanes. (20 points)

Answer 1

3.

Step-by-step explanation:

We start calcualting the factor for heavy-vehicle, that is,

`f_(HV) = (1)/(1+P_T(E_T-1)+P_R(E_R-1))`

`E_T = 2.5` for rolling terrain, so, replacing,

`f_(HV) = (1)/(1+0.18(2.5-1)+0)`

`f_(HV) = 0.7874`

We calculate the number of lanes by using the relation as follow:

`N=(V)/(\upsilon_p PHF f_(HV) f_p)`

`N=(2700)/(1915*0.88*0.7874*1)`

`N= 2.035`

In this way the necessary number of lanes is 3.

Note: To calculate
`\upsilon_p` you need to consult the Exhibit 23-2

in 'Highway capacity Manual' for 55mph and the LOS D criteria.