# 250+ TOP MCQs on Flow Density Relationships and Answers

Traffic Engineering Multiple Choice Questions on “Flow Density Relationships”.

1. Which of the following equations shows the correct relationship between flow, density, and space mean speed?
a) Flow = density/space mean speed
b) Flow = space mean speed /density
c) Density = flow x space mean speed
d) Flow = density x space mean speed
Clarification: Flow = density x space mean speed shows the correct relationship between flow, density, and space mean speed. It can also be written as q = kus.

2. On which of the following factors are flow, density, and space mean speed are not dependent?
b) Characteristics of the vehicle
c) Topography
d) Weather
Clarification: Flow, density, and space mean speed is not dependent on topography. They are dependent on characteristics of the roadway, characteristics of the vehicle, weather, and characteristics of the driver.

3. With respect to the shape of the flow-density curve, when the density reaches maximum the flow must be ______
a) Maximum
b) Infinite
c) 0
d) Minimum
Clarification: With respect to the shape of the flow-density curve, when the density reaches maximum the flow must be 0. This is because vehicles tend to line up end to end. Maximum density is also known as jam density.

4. On which of the following factor does mean free speed depend on??
a) Physical characteristics of highway
c) Characteristics of the vehicle
d) Characteristics of the driver
Clarification: Mean free speed depends on the physical characteristics of the road. Mean free speed is the absolute maximum speed that is acquired when flow tends to zero. As the flow increases the speed decreases.

5. The macroscopic approach considers which of the following factor?
a) Spacing
b) Speed
c) Flow-density relationship
d) Design
Clarification: Macroscopic approach considers flow-density relationship for describing traffic flow. It examines traffic streams and develops algorithms that describe the flow to the density and space mean speeds.

6. Which of the following is a model that is commonly used by the macroscopic approach?
a) Macroscopic Simulation Models
b) Mesoscopic Simulation Models
c) Greenshields model
d) Travel Demand Models
Clarification: Greenshields model is a model that is commonly used by the macroscopic approach. Greenshields model hypothesized that there is a linear connection between speed and density.

7. Greenberg model uses which analogy?
a) Fluid flow
b) Laws of motion
c) Secchi disk
d) Turbidity
Clarification: Greenberg model uses fluid flow analogy to develop macroscopic relationships for traffic flow. It is expressed in the following form, us = c ln(kj/k).

8. The Greenberg model is used for which type of traffic condition?
a) Dense
b) Light
c) Uncongested
d) Unrestricted
Clarification: The Greenberg model is used for dense traffic condition. The Greenberg model satisfies the boundary conditions when the density is proceeding towards the jam density. It does not satisfy the boundary conditions when density is proceeding towards zero.

9. When does the Greenshields model satisfy the boundary condition?
a) When the density is approaching zero as well as when the density is approaching the jam density kj
b) When the density is approaching infinity as well as when the density is approaching the jam density kj
c) When the density is approaching zero as well as when the density is approaching infinity
d) When the density is approaching zero as well as when the density is approaching the jam density kj
Clarification: The Greenshields model satisfies the boundary condition when the density is approaching zero as well as when the density is approaching the jam density kj. It is therefore used for both light and dense traffic.

10. The Microscopic approach does not consider which of the following factor?
a) Spacing between vehicles
b) Flow-density relationship
c) Design
d) Speed of vehicles