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Traffic signal pre-emptions

Traffic signal pre-emptions interrupt the normal operation of a traffic signal to allow for LRT and emergency vehicles to quickly travel through an intersection.

LRT pre-emption

A traffic signal that is located next to a train (LRT or CP Rail) crossing outside of the downtown area will have an added signal feature called LRT pre-emption.

When a train is approaching an intersection, the traffic signal initiates a pre-emption routine that signals to clear traffic from the train tracks before the train arrives. Next, traffic is served that does not conflict with the train until the train passes by the intersection.

Here are some components about LRT pre-emption:

  • Pre-emption programming and constraints differ between each intersection.
  • It is not always possible to serve pedestrian phases during pre-emption.
  • It is not always possible to serve non-conflicting arrow phases during pre-emption due to signal controller limitations.
  • Sometimes the return from pre-empt is simply the next signal phase and sometimes specialized programming is used to return in another manner.

LRT pre-emption interrupts the normal operation of a traffic signal. It may look as though the traffic signal may be serving or skipping certain phases excessively or that the normal coordination of the traffic signal is not working. 

Emergency pre-emption

This signal feature provides emergency vehicles a clear path to quickly travel through an intersection without time delays due to traffic signals. Certain intersections along emergency routes have been identified and have been outfitted with this signal feature.

The traffic signal will either extend the green time of the current direction of travel or end the phase it is currently in and cycle to the phase of the direction of travel of the emergency vehicle. Similar to LRT pre-emption, the normal operation of the traffic signal is interrupted. 

To find out more about how to add any of the above features or make an adjustment to a traffic signal in your area, please call 311.