How Traffic Signals Work

Traffic signal coordination is when traffic signals are timed so that traffic can travel along a street without stopping at every light. It’s challenging to do this when dealing with two-way streets, big intersections and lots of traffic.

To help maximize traffic signal coordination,  intersections are controlled by a computerized traffic control system. The system lets us monitor, as well as coordinate and communicate with the traffic lights.

traffic light controller box

Benefits of using a computerized traffic control system include:

  • Provide efficient traffic flow
  • Reduce  travel time
  • Reduce  fuel costs
  • Reducing vehicle emissions
  • Reducing rear end collisions

There are three basic types of traffic signal operations:

  • Fixed timed – signals change according to a pre-set timing.  The signals will cycle all the time even if there is no vehicle or pedestrian demand.
  • Semi Actuated – signals will only change if there is a vehicle or pedestrian on the  side street.  Side street green time will vary with traffic and there is a minimum and maximum value programmed.
  • Fully Actuated – signals are programmed to change with minimum and maximum green times depending on the traffic and pedestrian demand on all approaches.  The signals will change based on the demand from each approach.

Most of the traffic signals at Regional intersections (those are typically the major intersections across Halton) are either semi or fully actuated to  keep traffic moving.

How does a traffic signal know if there’s a car waiting?

traffic light controller box

There are two methods used by the Region to determine if a car is waiting at an intersection. We install a detector loop embedded under the road or mount a video detection camera of the signal pole.

The detector loop is a wire coil that’s connected to the controller equipment. A small electrical field is created by this electrical loop and when a car drives over the loops it sends a message to the controller and the controller responds. Vehicles should always stop at the white stop bar painted on the road so that the detector loops can be activated and change the signals.

Pole mounted video detection cameras serve the same function as the detection loops, but rely on video technology to detect t he presence of a vehicle. Video detection cameras are not Red light Cameras.

So how are the traffic signals coordinated in a system?

Using a computer optimization program and recent traffic counts, we develop the timing plan. Where we can’t coordinate traffic in both directions we coordinate the lights for the direction carrying the most traffic.

Traffic flow changes throughout the day so  different timing plans are used to accommodate the change in traffic volume.. 

Coordinating the traffic signal timings along a Regional Road is planned using the posted speed limit. Many factors can impact timings, such as traffic volume, emergency detours, direction of traffic, distances between signals and equipment malfunctions. Every year we review various corridors and update the signal timing as needed.