How does a traffic light sensor work?

[Homerr]

Ok, I have a question I've been trying to figure out for some time. <br /><br />Don't laugh, as I'm sure some of you also want to know! More questions than my 3 year old son!<br /><br />How do the traffic light sensors work?<br /><br />I know it changes when you drive over the sensor that is on the road in front of the light, but how does the sensor work? Magnetics? Motion?<br /><br />Thanks,<br /><br />H.

 

[Hooty]

Re: How does a traffic light sensor work?

Homerr,<br />I think they operate from a pressure switch. (Notice, I said Think).<br /><br />c/6<br /><br />Hooty

 

[JB]

Re: How does a traffic light sensor work?

Dang! I get to sound smart for a change!<br /><br />That big rectangle cut into the pavement contains a coil of wire that is sensitive to magnetic materials. Drive 4,000lb of steel over it and viola!! It thinks it is a vehicle. It is usually correct.

 

[ob]

Re: How does a traffic light sensor work?

Most of the ones in Corpus have been changed out to photo optic electronic sensors .I think they probably vary from place to place.

 

[12Footer]

Re: How does a traffic light sensor work?

JB is correct. I werk for a municipality,(not trafic control or M.O.T.) and they were explained to me thus:<br /><br />The square is a cut in the pavement into which, a wire is laid, and then,a tar filler to seal it off.<br />The ends are attached to a metal detection circuit,like a metal locator folks use at the beach lookin for quaters,<br />which is attached to the light's normal interval relay circuit. Sometimes, a guy can 'fake them out',making the light switch sooner, by moving a few feet, waiting a few seconds, and moving a few more feet. The detector will sometimes detect the subtle change in signal strength, and 'count' it as a second vehicle.<br />The optical switching system is usually used for triggering cameras for traffic enforcement.<br />They do have optical switching for trafic lights, but they aren't as reliable from what I've been told, and are costly.

 

[dmessy]

Re: How does a traffic light sensor work?

If you'er on a motorcycle, you have to park with your engine over the sensor wire to trigger the light that you are there.<br />With the photo optic sensors, try flashing your high /low beam headlights rapidly when approching the light(but only if there is no oncoming traffic , right?) It will turn green for you thinking you are a emergency vehicle.

 

[roscoe]

Re: How does a traffic light sensor work?

Now try doing that when you are driving a BMW bike, mostly alum alloy, when you want to make a left turn at the bottom of an exit ramp, and the light ONLY changes when the sensor is triggered (late night). You will soon be making the illegal left on red, or setting up camp for the night. I had to deal with one of these for 3 summers before they finally changed the program.<br /><br />Its kind of like waiting for the lift bridge to go up, but the tender went home sick.

 

[Greasie]

Re: How does a traffic light sensor work?

Roscoe,<br /> I ride a Goldwing and was frustrated while waiting for a car to pull up behind me to trip the sensor to make a left turn. Sometimes I would make a right turn then a U turn (traffic permitting of course). Once I learned how the sensors operated, I then would roll over the coil, lower the side stand and just allow it to touch the tar strip. This has not failed for me in over 15 years. Try it --- it works!!!!

 

[FLATHEAD]

Re: How does a traffic light sensor work?

Hey Greasie<br /><br /> Great idea I have been frustrated by traffic lights for years. You think I would of thought of trying this over the past 20 years Next time I roll the old electraglide up to a light I'll give it a try.

 

[crab bait]

Re: How does a traffic light sensor work?

i guess that in different parts of the country ,,it's different methods..<br /><br />the used to be pressure .. a big long metal rectangle in the road.. but all done away with cause heavy trucks hurt them..<br /><br />also ,,used to be photo eye arms before the lite,, lookin' down... when i was a kid.. we used to stand under one on he residential side of an intersection,,, that intersect a busy hi-way..<br /><br />we'd take off our belts a swing them over our heads.. an keep the lite red on the hi-way for as long as we wanted... <br />up to an hour one time,, by takin'turns.. driver's were so mad..!!<br /><br />man,, we had some stupid fun...!!<br /><br />but now ,, there all wire layed in a rectangle saw-cuts...<br /><br />HOMMER,, YOU'LL LOVE THIS..!! how things work

 

[roscoe]

Re: How does a traffic light sensor work?

Hey Crab BAIT, GREAT LINK to that website. But now I'll be sitting here reading all the neat stuff till Tuesday. Good article there on octane, and engines, and more engines, and water, and...<br /><br />All you guys and gals should check it out.<br /><br />Personnally I think it deserves its own topic.

 

[Scoop]

Re: How does a traffic light sensor work?

The coil of wire is a basic inductor that changes it's value when metal (Mostly ferrous) is around. An oscillation circuit would be set up, then when the frequency changed because of proximitely of metal, the light would change. <br /><br />The same principal is used in the metal detector at airports and the the oens that people use to look for coins. You can see an explanation at<br /> http://www.howstuffworks.com/metal-detector.htm <br /><br />The oscillator is a great circuit. You would be suprised at how many devices actually use these.

 

[Navigator]

Re: How does a traffic light sensor work?

They do have a range though. We have the problem here when concrete mixers pull up to the lights. There mass is so high above the sensors that they cant trip it. It will only trip if they can get their differentials squarely over the wire. It sure make traffic messy when they arrive at rush hour and they back up the lights for many blocks. Usually they end up running the lights after waiting 5 minutes or more.<br /><br />Talk about dangerous.<br /><br />Nav