How do traffic signals work?

Traffic signals are made up of many components and pieces of equipment to ensure that the signal operates safely and efficiently. Two of the most important components are the controller and detectors.

The controller is a computer that is programmed with various parameters that dictate how the signal operates, such as minimum and maximum green times, pedestrian walk times, and cycle lengths.

The detectors determine when a vehicle, pedestrian, or bicycle is present and pass this information to the controller. There are various types of detection systems, including video, thermal, electromagnetic loops in the pavement, and radar. Once the controller knows that traffic is waiting to receive a green light, it will incorporate that information into its programming as it runs through phases and cycles.

If a traffic signal appears to be operating unusually, such as not providing a green light to traffic or providing a green light to streets that have no traffic waiting, please contact Transportation and Engineering.

Show All Answers

1. What do I do when I see a dark or flashing traffic signal?
2. What happens to Jefferson County traffic signals when they lose power?
3. Who regulates traffic in Jefferson County?
4. Who builds and maintains traffic signals in Jefferson County?
5. How do traffic signals work?
6. Who maintains flashing school zone beacons?
7. How does the county decide when a traffic signal should be installed? Will a traffic signal reduce accidents at an intersection?
8. What is the purpose of cameras at signalized intersections?
9. Are traffic signals in Jefferson County coordinated to reduce or eliminate the need to stop at red lights?
10. Once a driver turns onto a street where the traffic signals are coordinated, is it correct that the driver should not have to stop?
11. Do any traffic signals not run in coordination with other traffic signals?
12. Why is there a “Walk” symbol when no pedestrians are present?
13. How do signals for pedestrians work?
14. Why do I have to wait so long to get a green light or a “Walk” signal?
15. Do emergency vehicles get priority at signalized intersections in Jefferson County?
16. Is it possible for two conflicting directions of traffic at a signalized intersection to receive green lights at the same time?
17. How does a flashing yellow left-turn arrow work?