How Traffic Detection Signals Work

The City of Toronto employs two main types of signal operations:  Fixed Time signals and Detection-Actuated signals.

Fixed Time signals are installed at the intersection of two major roads, and these traffic lights and pedestrian signals change based on a predetermined cycle time and are not influenced by traffic or pedestrian push-buttons.

Detection-Actuated signals are installed at the intersection of a major road and a minor road. The traffic signal on the major road remains green while the signal on the minor road stays red until a pedestrian or vehicle on the minor road is detected. Pedestrians must press the pedestrian push-button. Vehicles are detected on side streets by electromagnetic wires embedded in the road, behind the stop-line (you can actually see a square on the roadway). I have seen impatient drivers pull in front of the stop-line, hoping to trigger the green light, but it has the opposite effect.

At intersections where major streets intersect with minor roads, a situation may arise where the side street receives a green light but the pedestrian signal displays a “Don’t Walk” sign. This happens when a vehicle is detected on the side street but the pedestrian has not pushed the pedestrian push-button. Pedestrians must press thepush-button for the “Walk” signal to come on. The “vehicle-only” green light is usually shorter than the “Walk” green light cycle.

Left-turn signals can be programmed to operate at busy intersections during rush hours. Alternatively, sensors embedded in the road can detect vehicles in the left turn lane to trigger the advance signal. The sensor is embedded two or three car lengths back from the stop line, which means only the second or third car in the queue will activate the left-turn signal. The same system may also be employed for advanced green signals at major intersections.

In the future, this will change as Toronto is looking at new pole mounted detection sensors and new technology. Search “smart traffic lights and use game theory to ease traffic congestion.”