a four lane freeway located on rolling terrain with free-flow speed of 70 mph, 12 ft lanes, and no nateral obstruction within 8 ft of the pavement adges. The traffic stream consists of cars, buses and large trucks. A weekday directional peak-hour volume of 1600 vehicles is observed, with 600 arriving in the most congested 15 min period. if a LOS no worse than D is desired, determine the maximum number of heavy vehicles that can be present in the peak-hour traffic stream.