Test: Traffic Engineering- 1

Traffic capacity is the ability of a road to accommodate traffic volume. It is expressed as the maximum number of vehicle in a lane or a road that can pass a given point in a unit time, usually an hour.

Vehicles leaving the rotary would accelerate to the speed of the radiating roads and hence the exit curves should be of larger radii than entry curves. Hence the pavement width at entrance curve will be higher than at exit curve as the radius of the former is less than the latter.

Angle parking or parallel parking may be allowed in the kerb parking. Angle parking may be at angle 30, 60 or 90 degrees. Angle parking accommodates more vehicles per unit length of kerb and maximum vehicles that can be parked is with an angle of 90 degree.

Desire lines are plotted which is a graphical representation prepared in almost all O and D surveys, Desire lines are straight lines connecting the origin points with destinations. The width of such desire lines is drawn proportional to the number of trips in both directions.

The PCU may be considered as a measure of the relative space requirement of a vehicle class compared to that of a passenger car under a specified set of roadway, traffic and other conditions. If the addition of one vehicle of a particular class in the traffic stream produces the same effect as that due to the addition of one passenger car, then that vehicle class is considered equivalent to the passenger car with a PCU value equal to 1.0.

Traffic flow equation:
u = 80 - 0.7k
Since flow, q = u · k = 80 k - 0.7 k²

Percentile speed gives cumulative percentage of vehicle travelling at or below that speed. 
Between 85 percentile and 15 percentile speed, 70% of vehicles will be travelling. So 700 vehicles have speed between 10 kmph and 40 kmph.
The difference between 85 percentile speed and 15 percentile speed gives quality of flow.