Coordination of Traffic Signals

The quality of flow along a street is a function of the following:

Spacing of intersections along the street

Prevailing speed of traffic on the street

Traffic signal cycle length

Operation of the traffic signal equipment


Many drivers ask why they have to wait so long for a signal to change. Many of these drivers are waiting to enter a major arterial street from a side street. This is even more frustrating when no traffic can be seen on the arterial.

In order to coordinate arterial traffic signals, each traffic signal in the group needs to allow sufficient green time for all movements during a common fixed time period, called a common cycle length. The cycle length chosen is usually determined by the largest intersection in a group of signals with the most conflicting movements. This will most often be an intersection that has left-turn arrows for all directions and wide cross streets. For that reason, the common cycle length that is fixed for each traffic signal in a group may be rather long.

Furthermore, to allow the coordination of the arterial, the side street is required to wait until the main traffic movement on the arterial has gone through the intersection. It is possible that the arterial traffic cannot be seen immediately, but will soon be passing through the intersection. The major arterial streets coordinated in the City include:

  Alton Jamboree
  Bake Jeffrey
  Barranca MacArthur
  Campus Main
  Culver Michelson
  Harvard Red Hill
  Irvine Boulevard University Drive
  Irvine Center Drive Von Karman