A four$-$lane urban freeway $($two lanes each direction$)$ is located on rolling terrain, has $11-$ft lanes, no lateral

obstructions within $4$ ft of the pavement edges, and $5$ on$/$of ramps within $3$ miles upstream and $3$ miles downstream

of the midpoint of the analysis segment. The traffic stream consists of cars, buses, and large trucks $($no recreational

vehicles$).$ A weekday directional peak$-$hour volume of $1800$ vehicles $($familiar users$)$ is observed with $700$ arriving in

the most congested $15-$min period. If a level of service no worse than D is desired, determine:

a$)$ the maximum number of large trucks and buses that can be present in the peak$-$hour traffic stream

b$)$ traffic density under these conditions

c$)$ traffic speed under these conditions.