Traffic Lights


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How do street traffic lights work? Are they all on different timings or is there a sensor that detects if there is a car. I have bet with a friend so thanks for the input.

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Most 4 way interesections (major interesects major) are on timers the left turn lanes detect how long or how many cars are there if there is only 1 car it will take longer for a left turn arrow, if there are 2 or more cars a left turn arrow will turn on, on the next turn

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Both. Some are on timers, others work on pressure sensors.

Busy intersections are most likely on timers though.

Thoes little rectangles inbeded in the pavemen at the intersecions, are electro-maget sensors. They also calculate how fast the car goes when the light is yeellow so it stays yellow.

BTW im a n00b. I saw that when my freind SimK68 was giving yall trouble. YOu got to learn to work with him. He's a ok and funny guy once you get to know him. He told me he was sorry to you guys. He has a hard time adapting is all. :) I looked at the posts he made ,and I cried from laughing.

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they are on a cycle. the 4 way intersections in the US are almost always the exact same pattern.

if you are turning left, your light will turn green after the cars traveling perpendicular to you, straight through the intersection, pass through.

if you are going straight, your light will turn green after the cars turning left from the direction you were traveling and the cars turning left from coming the opposite direction have all passed. if there are more cars turning left from your side of the road, an intersection with sensors will detect this and allow your side of traffic traveling straight to proceed as those turning left from your side continue.

that might not have made any sense, but just look in the road when you stop, youll see little sensors as you get close to the line, and watch for the pattern, youll pick up on it after a while and youll always know when its your turn

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In my city, some street traffic lights have been controlled by intelligent sensors and the sensors are controlled by computer to decide letting cars go or stopping them...

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theres so many ways traffic lights work just depends on what area of the light is, traffic in that area, cities budget to spend on a intelligent system, u can make almost all traffic lights turn green with a pulse of RF light, theres some boxes u can build that flashes light at them to change the light green like police cars and fire engines do :D

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Well, in Australia the 'main road' will always be green if there is no one touching the censor from other cars on the intersection.... So when your traveling on a main road at 2am you will get clear passage of green lights all the way... But if you are coming from a road that is not the main road, the light will be red, as soon as you hit the censor, the lights will turn yellow (if there hasnt been any cars passing for a while)

In heavy traffic where cars constantly pass over the censor, the lights will turn yellow after a certain period of time to give a turn to other cars :)

Edited by Mango
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have you ever noticed those big circles near the intersection?

those are sensors and when your car goes over it.. computer gives turns depending on current traffic..

for example.. the light for north and south is green and you are heading north, you reach an intersection and get into the left turn lane (turning west) you have now activated the sensor. if there are already cars waiting (going east and west) they are given the green light first and then it will be your turn provided that you have a protected green light (arrow)

but.. if no one is traveling south (from your point of view) then the computer will change the light to red on the opposite traffic giving you the green light to turn and it also stays green depending on how many cars are waiting to turn.

in less crowded intersections the more cars, the longer the green.. but if you go to LA most protected (by protected i mean, that you have a turn indicating light) lights last no more than 3 seconds, enough for 2 cars at a time..

i hope that made sense :unsure:

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Over here it's a mixture. Some old ones in my town are still fixed timed, possibly also use the induction loops (the loops of wires found on the road near traffic lights), however, along the main roads, most of the traffic lights are connected together via a SCOOT software system which optimises the cycle times for optimum traffic flow during the day, which is some kind of software. Elsewhere, several systems use infra-red detectors, placed on top of the traffic lights to detect viechels waiting at the traffic signal, probably use both infra-red and surface sensors.

Edited by Deryck
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Both. Some are on timers, others work on pressure sensors.

Busy intersections are most likely on timers though.

Above is accurate. Busy areas (like downtowns in major cities) are on timers, period. On some stretches you can even go from one block to the next and watch lights turn green in sequence if you're going the speed limit.

More isolated/variable locations can have pressure sensors impact what they do, comparable to if someone presses the button saying they'd like to cross the intersection as a pedestrian, but otherwise they don't take such into account.

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Then at night all our lights turn blinking yellow, love driving during those times.... but not all the lights do. And can't speak for big cities like LA if this happens also. But mainly gives blinking yellow to main road traffic..... during day, like everyone said, mixture of pressure, induction-wires, infrared, timings, and i've heard of that software that links main road traffic lights together to optimize traffic flow. Wow i'd love to program that software. I wonder if they would make that signal that system works on wireless, if someone could hack the system, hahaha, go through all gree lights, wow that would be fun, though probably wouldn't happen since you can make it turn green just like that, must first have it do its cycle of yellow and red for perpendicular traffic. But you get what i'm saying...

And we use timings, and induction wires here, no infrared from what i've seen, nor have i see the pressure plates. Those would be nice though, but meant for bigger cities.

PS: try getting a light to change when your on a bike that isn't on timing, oh thats fun! Usually they are mix of timings and induction loops so if you wait a long time or car pulls up you will get the green.

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  • 2 weeks later...

Sorry to resurect this thread but this is something relevent. Below is a photo of an infra-red sensor used to detect viechels a traffic lights. It just took me that long to find the photo; it's the grey box like object just above the traffic light:

Traffic_Light_sensor_2.jpg

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theres so many ways traffic lights work just depends on what area of the light is, traffic in that area, cities budget to spend on a intelligent system, u can make almost all traffic lights turn green with a pulse of RF light, theres some boxes u can build that flashes light at them to change the light green like police cars and fire engines do :D

you can actually buy the RF boxes to change the lites yourself!!!

could be super dangerous when changing the lites on your own!!

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