Traffic density is the number of vehicles occupying a given length of the highway in a traffic lane.
It is expressed as vehicle/mile or vehicle/kilometer.
For example 4 vehicles are present in 500 feet. So traffic density in one mile will be 42.24 vehicles.
k = 42.24 vehicles per mile.
Density is inversely proportional to the volume of traffic. If density is less, then speed will be more and traffic volume will be more. And if the density is greater, then the speed will be low and traffic volume will be less.
Whenever, traffic jam problem create at certain point, then by the consideration of the peak hour traffic volume, we may proceed towards widening of road, fly over or under pass.
Headway and Spacing
Consider two successive vehicles in a lane.
Spacing is defined as the distance between successive vehicles in a traffic lane as measured from front bumper to front bumper in a traffic stream.
It is measured in feet. It depends upon the speed.
It is the corresponding time between two successive vehicles as they pass a given point on the highway.
Clearance and Gap
The clear distance between two successive vehicles in feet is known as clearance. Time between the two successive vehicles in seconds is known as Gap.