How does a traffic signal sense cars?

Loops:  This detection type involves multiple 6-foot by 6-foot wire coils (loops) installed under the road surface. When a vehicle drives over the loops, a vehicle detector is activated and sends a message to the traffic signal to change the signal accordingly. Loops are the oldest form of traffic detection and are no longer installed with new signals because they require drivers to stop in a specific area, don’t work well for motorcycles or bicycles, and are often destroyed by excavation or roadway deterioration.

Video detection cameras:   These cameras are mounted for each approach to an intersection, and when they detect a vehicle, the signal will change. Cameras were installed in Missoula from 2001 until 2012 but are no longer installed because they can be affected by the sun and other light glare, fog, smoke, and build up on the lens from blowing snow and dirt.    

Radar: The newest and best option for vehicle detection at this time is radar because it accurately detects all roadway users and is reliable.

Show All Answers

1. How do traffic signals work?
2. How does a traffic signal sense cars?
3. Why do some lights stay green when there are no cars present?
4. How does an emergency vehicle, such as a fire truck or ambulance, change the signal to give them a green light in the direction they are traveling?
5. Can I make a light change to green by flashing my headlights?
6. What happens when a train approaches a traffic signal near a railroad crossing?
7. How are traffic signals coordinated in a system?
8. How do pedestrian buttons and walk signals work?
9. Why do I need to push a button to get a walk light?
10. What new technologies are coming our way?