Do stoplights really have sensors that change the light when cars are there?

Question

I've heard this a lot but I don't believe it

Answer 1

yes, and as a result, some jurisdictions are allowing motorcycles to proceed on a red light after a certain wait, when and if the traffic flow permits it safely, since motorcycles don't trip the sensor.

Answer 2

Yes,but only some stop lights do.

Answer 3

Ever notice on the ground, around the place where the car stops at a red light, there are grooves cut into the pavement to make an octagon?  When they cut those grooves, they put a loop of wire into them, and then put a sealant on top.  A current is run through the loop of wire, which (as we know from Physics class) causes a magnetic field.  When a car (aka big hunk of metal) enters this magnetic field, it screws up the inductance.  When that happens, the sensor "knows" that there is a car there.

Answer 4

not all stoplights but some do.

Answer 5

Yes.  There is an inductive coil buried just below the pavement.  It senses the steel inside the inductive coil.

People who ride certain motorcycles know this.  Most motorcycles do not contain enough steel to trip the sensor.  You can be stuck at a red light for a long time.

Answer 6

i think so