# Traffic Engineering Questions and Answers – Traffic Flow Element

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This set of Traffic Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Traffic Flow Element”.

1. How many primary traffic flow elements are there?
a) 2
b) 4
c) 5
d) 3

Explanation: There are 3 primary traffic flow elements. The inter-relationships between these elements aids in planning, designing, and assessing the benefits of implementing traffic engineering measures on a highway system.

2. Which of the following is not an application of traffic flow theory?
a) to determine adequate lane lengths
b) to study the interrelationships of traffic flow elements
c) to determine PCU
d) to determine the average delay at intersections and freeway ramp merging areas

Explanation: Determination of PCU is not an application of traffic flow theory. Determination of adequate lane lengths, study of the interrelationships of traffic flow elements, and estimation of delay at intersections are some of the applications of traffic flow theory.

3. Time-space diagram is a graph that describes the relationships between time of the vehicle as it progress in the highway and ______
a) green time
b) location of intersections
c) location of vehicles in a traffic stream
d) density of traffic stream

Explanation: Time-space diagram is a graph that describes the relationships between time of the vehicle as it progresses in the highway and location of vehicles in a traffic stream. Time of the vehicle is on the x-axis and location of vehicles in a traffic stream is on the y-axis.
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4. The number of vehicles travelling over a unit length of highway at an instant in time is ________
a) flow
b) speed
c) density
d) acceleration

Explanation: The number of vehicles travelling over a unit length of highway at an instant in time is density. The unit of density is vehicle/m or vehicle/km. It is usually denoted by k.

5. The slope of time-space diagram is ______
a) flow
b) speed
c) density
d) location

Explanation: The slope of time-space diagram is the speed of a vehicle at any time t. Speed is the distance travelled by the vehicle in unit time. It is expressed as km/hr or miles/hr. It is usually denoted by u.

6. The harmonic mean of the speeds of vehicles passing a point on a roadway during an interval of time is known as ______
a) Density
b) Flow
c) Space mean speed
d) Time mean speed

Explanation: Space mean speed is the harmonic mean of the speeds of vehicles passing a point on a roadway during an interval of time. It is the entire distance travelled by the vehicles divided by the total time required by these vehicles to travel that distance. Space mean speed is involved in flow-density relationships.

7. The time-mean speed is always less than space-mean speed.
a) True
b) False

Explanation: The statement, “The time-mean speed is always less than space-mean speed” is false. The correct statement is, “The time-mean speed is always higher than space-mean speed”. The difference between time-mean speed and space-mean speed tends to lessen as the absolute values of speeds increase.

8. Flow can be determined by which for the following mathematical formula?
a) q = n x 3600/T
b) q = n x 360/T
c) q = T x 3600/n
d) q = n x 60/T

Explanation: Flow can be determined by the given mathematical formula, q = n x 3600/T. Here, q = flow in vehicle/hr, n = the number of vehicles passing a point in the roadway in T sec

9. What is the unit of time headway?
a) meter
b) veh/m
c) seconds
d) m/veh

Explanation: Time headway is the difference between the time the front of a vehicle arrives at a point on the road and the time the front of the next vehicle arrives at that same point. Its unit is expressed in seconds.

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