• Traffic Flow: The rate at which vehicles pass at a fix point (vehicles per hour)
• Traffic Density: No. of vehicles(N) over a stretch of roadway(L) i.e. vehicles per kilometres = N/L
• Time Headway: Time interval between the passage of the fronts of the successive vehicles at a specified point.
• Average Time Headway: Average travel time per unit distance $\times$ average space headway.
• Space Headway: Distance between front of successive vehicles.
• Average Space Headway: Space mean speed $\times$ average time headway

---

Solved Example: 9065-01

Which of the following characteristics of an ideal flow-density relationship for fundamental diagram of traffic flow is INCORRECT? (DFCCIL Jr. Manager Civil Sep 2021)

A. When the number of vehicles gradually increases the density as well as flow increases.

B. When the density is zero, flow will also be zero, since there are no vehicles on the road.

C. When more and more vehicles are added, it reaches a situation where vehicles can't move. This is referred to as maximum density.

D. There will be no density between zero density and jam density, when the flow is maximum.

Correct Answer: D

Solved Example: 9065-02

The average spacing between vehicles in a traffic stream is 50 m , then the density (in vehicle per Km) of stream is: (RPSC DLB Civil Shift I 2016)

A. 15

B. 17

C. 10

D. 20

Correct Answer: D