
Critical Density and Critical Speed
The capacity of a road segment is commonly defined by the number
of vehicles it can handle over an unit of time, such as 1,000 vehicles
per hour per lane. This can only be achieved under specific conditions
of traffic speed and density:
- Critical Density. The volume generally increases with
the density of the traffic. However, at some point the density is
too high and congestion decreases the volume.
- Critical Speed. The volume generally increases with the
speed of the traffic. There is however a speed at which the volume
is maximal.