How do street lights know to change when you pull up?

Question:
I'm sure theres some type of sensors somewhere but I was wondering if anyone knew exactly where and what they are?

Answers:

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Traffic signals are controlled by a coil of wire, buried in the pavement, which senses a change in magnetic field due to the presence of a vehicle. If you look at the pavement near an intersection, you may be able to see them if they have not been paved over since being installed.

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some street lights have sensors on them, And some street lights are automatic and are timed to change at certain intervals.

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Some intersections have plates in the road that sense the weight of a car, which signals a light change (eventually). They are set up so that a person could walk over them without setting it off.

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some have sensors mounted above the lights themselves, and other w3ork off of pressure sensitive plates that are built into the asphalt(notice the circles in the ground at intersections) others just got off of a timmer..

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There is sensors in the road...the white line just look at it you my see a line running through it and just before the line about 20 feet there is another sensor line on the road

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The same way that a tree knows to shed its leaves and a bear knows to hibernate in the fall. It's evolution, man! The fossil record is replete with ancient traffic signals.

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yupp sensors, and why do u have to know where and what they are, just be happy that there's one, it will be too frustrating if u stop on a light and u dont see any vehicles at either side and u are stuck there waiting

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rhsaunders is correct. The sensor loops act like a metal detector.

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This web page explains it all: http://www.howstuffworks.com/question234...

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magnetic sensors buried in the road surface right around where the lights are in the outgoing lane so that when a car pulls up it can detect if there's a sufficient attraction form the mettals and such to signal there's a car there and to use the lights othereiw it runs on a preset pattern of time limtis before changing when nothing is there.

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Yes, there are secret sensors at every intersection that make the lights turn red as we approach--they have been placed there by international terrorists in an attempt to make all of us late getting to work, thus undermining the US economy, increasing road rage, and generally driving us crazy.

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They have sensors installed beneath the ground and as soon as a certain amount of cars go thrrough the light or a rather large vehicle goes through the interesection the trigger sets off the sensor causing it to instantly turn yellow. Most traffic lights, however, are controlled not by sensors but by timers which has a different timer for both interesections. However much time is programmed on it will begin counting down the instant the light changes from red to greeen. After the timer has reached 0 the light notices this and yet another sensor tells the light to turn yellow. Generally speaking, the busier the interesction, the longer the light will stay green. The longest green light I have seen is 1 minute, 30 seconds and I know because I timed it. The shortest is 40 seconds but this is only for very inactive intersections.
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