Traffic Lights

[kingmickez25]

So i have a question and its a pretty stupid one.

 

How do traffic lights work?

 

This all started today when i was at my job as a sign holder.

 

i was a t intersection

 

So the top part of the T is the main road and the bottom part of the T is a parking lot of a house complex

 

well theres traffic light on the top part of the T and the bottom part of the T so people from the parking lot can to the main street safetly

 

So i always thought traffic lights were on timers like 1:30 min for north and south traffic and 1:30 min for east and west and it switches over and over all day.

 

but that doesnt seem to be the case. beacuse on the main road the green light was always on until a car approched from the parking lot then the light would know

hey theres a car there and it switches lights so the car in the parking lot passes saftley to main road.

 

My question is how does the light know theres a car waiting for the light

 

a presser plate on the road?

Motion sensor?

 

P.s Sorry if this doesnt make sense i tried my best to make it clear

[H2PM]

To answer your question on how they work:

I have no freaking idea.

But the timer thing:

It varies on how much traffic is in the area, the lights would be faster if there was more traffic, and slower if there was less.

Is what I think they base it off of...

I may be wrong.

[Giordano]

Three little elves hide inside each of the street lights, each one holding their own light bulb. They see which way has the most cars, then the bottom elf puts on his light bulb to make a green light. The trick is, they have to communicate with each other so when ones green the others red.

 

They do a pretty good job, but sometimes, they like to mess with us human folk.

[obfuscator]

Pressure plates, usually. I know some lights have motion sensors, but it really depends where you live.

[Speedyshel]

It's pressure plates in the road that do most of the work, but the time of day determines some of it too. Like the traffic lights late at night won't change as much as they would during the day. That's the extent of my knowledge...not very much! :D

[Omar]

i was a t intersection

Salvia's one helluva drug.

I haven't read everything but this seems like what you want.

http://en.wikipedia.org/wiki/Traffic_light_control_and_coordination

[Giordano]

Pressure plates? Really? Why didn't I think of that earlier. My life's mission is complete. :-)

[kingmickez25]

Well Thanks Guy's

 

and no i wasnt high

[obfuscator]

Pressure plates? Really? Why didn't I think of that earlier. My life's mission is complete. :-)

Yeah if you look right behind the line you can sometimes see the big square area(looks like a bad patch job).

[Saru Inc]

Pressure plates, but mine also run on a system. For example, if I leave my house at 1:11 pm, I WILL hit all greens, no matter what. If I leave from 1:13 to 1:26 I won't. I don't know why, I mean you'd think 1:22 would be all greens, but it isn't. I've not tried later than 1:26 cuz then I'll be late for work. Heh.

 

 

Me and my friends have been questioning whether or not the elves inside the lights are racist or not. When we listen to rap/non rock music we get all reds. When we listen to rock/coheed/"instrumental" /metal, we hit almost all greens.

 

 

Lawsuits are being tailored as we speak.

[KittyKat]

Generally speaking, timers or inductive loops

[Shiny]

Pressure plates, but mine also run on a system. For example, if I leave my house at 1:11 pm, I WILL hit all greens, no matter what. If I leave from 1:13 to 1:26 I won't. I don't know why, I mean you'd think 1:22 would be all greens, but it isn't. I've not tried later than 1:26 cuz then I'll be late for work. Heh.

 

 

Me and my friends have been questioning whether or not the elves inside the lights are racist or not. When we listen to rap/non rock music we get all reds. When we listen to rock/coheed/"instrumental" /metal, we hit almost all greens.

 

 

Lawsuits are being tailored as we speak.

 

Are YOU high? I don't know about the original poster but, that sounds pretty wack.

 

I always used to think dwarves lived inside.

[____]

Generally speaking, timers or inductive loops

That's what I thought too.

 

 

Edit: Pressure plates never made any sense to me as I've seen many large vehicles (usually Army) not be registered since they say so far above the ground. Quite a few lifted 4x4's around here also have that problem at certain traffic lights. Had it happen to me quite a few times. Being outside the magnetic field ftl.

[Skull]

Am I the only one who always knew that they were on timers or used sensors?

[tripsis]

Am I the only one who always knew that they were on timers or used sensors?

I knew! :P Well I always kind of assumed they were anyway. When you consider that during the day (active traffic hours) the light routine is pretty much always the same, but at night the lights seem to cater to directions that have cars, I thought it was pretty obvious.

[Saru Inc]

Pressure plates, but mine also run on a system. For example, if I leave my house at 1:11 pm, I WILL hit all greens, no matter what. If I leave from 1:13 to 1:26 I won't. I don't know why, I mean you'd think 1:22 would be all greens, but it isn't. I've not tried later than 1:26 cuz then I'll be late for work. Heh.

 

 

Me and my friends have been questioning whether or not the elves inside the lights are racist or not. When we listen to rap/non rock music we get all reds. When we listen to rock/coheed/"instrumental" /metal, we hit almost all greens.

 

 

Lawsuits are being tailored as we speak.

 

Are YOU high? I don't know about the original poster but, that sounds pretty wack.

 

I always used to think dwarves lived inside.

 

 

No. Why is it wack. Is the truth wack? I THINK NOT.

 

 

IN all seriousness, I agree with Tripsis.

[stevepole]

In general lights run on timers or sensor. The lights around where I live/ Campus are set to different times depending on the hour of the day to maximizes the flow of traffic.

[Lenin64]

Pressure plates? Really? Why didn't I think of that earlier. My life's mission is complete. :-)

Yeah if you look right behind the line you can sometimes see the big square area(looks like a bad patch job).

That's what those are? I've been wondering that since before I started driving but nobody I aksked ever knew.

[Saru Inc]

That's what you get for driving in Russia.

[sees_all1]

Inductive loops are stupid cheap. When a large hunk of steel, like an engine block, goes over them, a current is induced. Usually when you see metal circles in the ground, that's what they are. Pressure plates wouldn't make much sense cost-wise.

My city likes to use cameras. Don't know why, they probably do a better job seeing further off.

 

Anyway, if you ride a motor cycle and you find the light won't turn, put a strong magnet on the bottom of your bike. Presto... insta sensor trip.

[RpgGamer]

timers and motion sensors buddy, Sometimes you can spot the cameras and sensor arrays on the traffic light itsself. They range from a quarter to a literal camera

[michel555555]

There are a few different ways. The pressure plates and motion sensors are usually what are used in lower traffic and new areas. To make it so people don't have to spend a while waiting at a red when there is no one coming from the other direction. Basically the lights timers change depneding on the amount of trafic.

 

But for high ways and places where there is constant trafic those methods just arn't needed. Those run on timers. Each lights timer is calculated differently and there is actually a formula for determining how long a lights timer should be. It has to do with visability and other road conditions but i don't know the actual formula.

 

Each timer has to be set individually because of yellow lights. If the timer between yellow and red is to short on a road that is shorter then people may go through a red light and might cause a crash. To long and people might get used to how a certain light works and might just blow through it no matter what, again risking a crash if the light is changed or if they think that all lights work the same way.

 

Also, main streets have longer timers then side streets that they intersect to help reduce congestion.

 

Spent a season working with a construction company if anyone is actually interested how i know this. Was mostly grunt work but had a chat with a technitian when they were putting in a new light on our route.

[xSxqPowerx]

Yeah, usually sensors for a road that is not used frequently that merges onto a big road. When 2 big roads cross it is generally just on a timer based on the amount of traffic each way.

[kingmickez25]

So to sum it up

 

Motion sensors, Timers and Pressure plates?