Some street lights don’t change unless there is a car there, how does this happen?

Question

Some street lights don’t change unless there is a car there, how does this happen?

In: Engineering

Answer 1

The old style of sensor is a loop of wire in the pavement. There’s an electrical signal going through the wires at a consistent frequency. When a car drives over the wire loop, the iron in the car’s frame has an impact on the frequency of the signal through a process called induction. When the frequency drops, it sends a pulse to the traffic light controller, and that’s how the controller knows that a car is waiting.

The new style of sensor is a really fancy camera on the signal arm. The camera can detect when there’s a car waiting to cross.