Is this true or not? I have been told that there are underground sensors at the stop lights and your car?

Question

sets them off and changes the light. I don't really believe it, but many people say yes.

Answer 1

That is true.  I am a civil engineer and most intersections have these sensors that detect cars.  The sensors send information to a computer nearby that determines when the light changes.

Answer 2

Depends on where you're at.  Some lights are simply timed on a continuous loop, others such as those where I live have the sensors that help to change the lights (these are especially good for left turn signals so they don't change if no one's there).  You can usually see these on the ground, they look like black cables embedded into the asphault.

Answer 3

yeah they are traffic sensors, a car alone does not make the light change, but the measure of how many cars there are per feet at a street or intersection will affect the timer for each colored light. So let's say you are attempting to make a left on a light that reflects green/yellow/red arrows. you might stop at a red one, if there are no other cars within certain feet of the intersection it will automatically switch to green and then control other oncoming traffic from there.

The sensors aren't everywhere however, only at highly congested streets.

Answer 4

Some traffic lights have a fixed rotation of who gets the green, or for how long some light stays green.

Have you ever come to a traffic light intersection & the lights go red for you & there's no traffic on the side streets?

That is a case where no sensor is being used to see if any side street traffic needs a green.

Some traffic lights only cycle through left turn green light when there is a car in the left turn lane that needs it.

How does the system know that?

Some kind of sensor.

Different places used different systems.

While today's cars do not contain part of this electronic package, in Europe there are now "smart cars" that read information in the roadway to help the driver avoid trouble around the corner.  Technology marches forwards.  Maybe some day what you writing about may come true.

Answer 5

Yes! Weight sensors.

Answer 6

It is a fact. At most major ingtersections there are sensors embedded that help control traffic flow.

Answer 7

At many signals, imbedded in the pavement there are sensors, but there aren't any in your car that "talk" to them

Answer 8

There aren't any in your car.  A few years ago, you could purchase a transmitter, such as those on emergency and police vehicles that would change lights for you.

Currently, many signals have what's called an inductive loop a few feet before the stop line or crosswalk. It works like a metal detector. It senses a large mass of metal above it and uses that to let the software operating the light know that it needs to change.

It's the same technology that operates the exit gate in many communities and is the bane of sport bikers. I'm told, (of course I haven't tried it,) that a baking sheet will open automatic gates. And I know more than several sport bikers that have glued magnets to the underside of their fairings to make the inductive loop notice them.

Some lights have them in just one lane, and I've seen them in as many as three seperate lanes; one for the left turn signal, one for the primary light, and even one for a right turn signal.

My grandmother believed that traffic lights "sensed" her left turn signal to activate the green arrow; of course, my dog also thinks that I excrete doggy treats.

JT