A six-lane freeway (three lanes in each direction) in a scenic area has a measured free-flow speed of 55 mi/h. The peak-hour factor is 0.80, and there are 8% large trucks and buses and 6% recreational vehicles in the traffic stream. One upgrade is 5% and 0.5 mi long. An analyst has determined that the freeway is operating at capacity on this upgrade during the peak hour.
If the peak-hour traffic volume is 3900 vehicles, what value for the driver population factor was used?