#hiddenstem

The carved loops seen in the road’s surface is a mere coil of wire referred to as an inductive loop detector.  Other than timed signals, the inductive loop is the most common way of control traffic signals.

The loop is connected to a detector via an extension cable which is usually seen running back to the curb on a diagonal.  This cable delivers power to the loop producing a magnetic field near the loop.  When your vehicle, or for that matter any electric conductor, moves over the loop, the magnetic field is disturbed. This disturbance closes a relay which is normally open turning the light green. It will remain this way until the vehicle leaves the loop.

So does moving your car back in forth over the loop assist in changing the light? Maybe…if you have not stopped at the appropriate location within the loop. Often detectors are positioned and calibrated to detect the front axle. Thus, positioning the axle directly over the loop is most effective. For bicyclist your tire rims, if made of metal, tend to be most effective at triggering the light.  It is best to align your bike with the right-hand edge of the loop.  

In the end, physics explains the mystery of traffic detectors.  Of course, it might just be magic!