How do stoplights detect a car?

Answer 1

Usually, there's a sensor that senses when a large metal object has passed over it. Things like an engine block. That's why motorcycles, not having much metal, can be stuck at lights cuz they can't trip that sensor.

If they have two sensors, they can figure out your speed (how red light or speed cameras usually work).

Answer 2

If you have time to read all the others, here is one more: Some are simply on a timer. Most have sensors buried in the pavement. Magnetic or weight is irrelevant. If you look up on the light support and see a small shiny box, it is a device to detect strobes on ambulances and fire engines. When an emergency vehicle approaches, the device detects the strobes from a long ways back to change the light. (Don't always work in daylight, maybe my strobes aren't bright enough.) And another method nobody has mentioned. The lights are computer controlled from a central location. Ever been on a street with a sign that says"Stop lights are set for "X" mph?" If you drive that speed or a couple of mph faster you will make every light.

Answer 3

They have two different sensors used. There is a ground sensor that detects the wheels and the weight of the vehicle. Also most of the signals have a eye sensor that when it gets late at night and the traffic signal is set to only respond to change when traffic comes upon the lesser of the traveled of the intersecting roads.These sensor eyes are light affected.So when you get close up on it your head lights are detected on the eye and put the signal into a 30 second cycle to change from red to green after giving the apposing signal the yellow warning.

Answer 4

There are three ways that I know of:
1.Under the pavement is a magnetic sensor that picks up the metal in your car and starts it working.
2.Some are pressure sensors that pick up the weight of your car. That's why motorcycles and bicycles have a problem making lights change.
3. Infrared sensors on top of the light are sent signals by police cars, fire trucks and in some places buses that will activate the light, just like your TV remote. So there....

P.S. If someone is stopped too far back from the light and not far enough over the sensor, honk and make them move up!!!

Answer 5

They usually bury a metal sensitive wire in the lanes going into the intersection. If you look at the street, you can see the patches ove the cuts in the asphalt.
These wires sense a car over them and start the "change" sequence after a timer runs it's course