How and when traffic signals change depends on the locality. Here are some methods:
- Timed cycle lengths
Signal changes are timed and anything drivers do is uncaptured and ignored.
- Loop (Actuated) detectors
Twisted wires are put under the stop line with electricity running through them. This creates a magnetic field surrounding the wires. When a vehicle approaches the line, the magnetic field alters and a mechanism in the traffic light is set off. What the driver should do is place the car right in front of the stop line and sit tight. Constantly moving the car may not set off the device. NOTE: Some vehicles such as motorcycles and bicycles don't trigger the lights.
- Camera sensors
Perched on top of signals, the sensors detect motion at the intersection approach opposite the signal. The cameras are usually low resolution and can not pick up license plate numbers and the like.
- Computer technologies
There's nothing a single car can do, but some roads have detectors far ahead of a traffic signal that counts how many vehicles are approaching a light. When a certain number is reaching the signal ahead changes.
It should be noted that pressing the pedestrian crossing buttons has no effect on hurrying a signal.
There are many reasons why a light may not go off. Usually the primary road always has a set time as to how long the signal stays green, and any vehicle that approaches on a side street must wait until this period ends. Also, pedestrians always drastically affect a traffic signal's behavior. Plus, things like bad weather and malfunctioning equipment will always occur.