Principles of Transportation Engineering

Terms Only

Speed

Distance travelled per unit time.

Time Mean Speed

Arithmetic mean of the speeds observed at some designated point along the roadway.

Space Mean Speed

Harmonic mean of the speeds observed at some designated point along the roadway. (Free Mean Spee)

Traffic Flow

Rate at which vehicles pass a given point in a roadway given in terms of vehicles per unit of time.

Traffic Density

Measure of the number of vehicles occupying a length of roadway.

Space Headway

Distance between successive vehicles moving in the same lane measured from head-to-head at any instance.

Time Headway

Time interval between the passage of successive vehicles moving in the same lane measured from head-to-head as they pass a point on the road.

Jam Density

Density at which the speed of traffic is approaching zero.

Free Flow Speed

Speed at which density of traffic is approaching zero.

Capacity/Maximum Flow

Ability of a roadway to accommodate traffic. The maximum number of vehicles that can pass at a given point in unit time.

Peak Hours

Often referred to as “rush hour“.

Peak Hours

The specific time periods during a typical day when traffic volumes, transit passenger ridership, or pedestrian counts reach their highest levels.

AM Peak Hour

Occurs between 7:00 AM and 9:00 AM as commuters travel from residential areas to workplaces and schools.

PM Peak Hour

Occurs between 4:00 PM and 6:00 PM as commuters return home or run errands.

Peak Hour Factor