Does anyone know how stoplights work?

[Sir_Froggy]

i know they turn green and everything, but how do they do that?

i think it's some sort of sensor right?

but the real question is where is the sensor?

i use to think it was on the light post thingy cuz some of the light post things have this little boxy thing on it...so i thought it was for the signal ur light gives off.

but another friend told me the sensor was in the ground. cuz when u cross a stop light, the ground is all marked up, with lines going out and ending in circles like so

0 0
/ /
/ /
/ /
/ /
/ /
------------0
\ \
\ \
\ \
\ \
\ \
0 0

so is that where the sensors are? and if they are there, how do they sense the car? weight??


well um that one diagram doesn't work too well so its just like a th ing that sticks out on both sides with the distance between them about a car length

[sho.gun]

Yeah I think the sensors are underground. Those round things, they know you... be afraid.

[g222leav]

according to my physics professor...

there are metal plates or something embedded in the ground at the stop light...when a large metal object (like a car) passes over it, and stops above it, the car changes the magnetic field of the metal plates...this sends a signal to a control box on the corner (you've probably seen this)...the signal tells the the lights to change. this is probably why most motorcyclists have notice why when they're at a light, it won't change for them...cause they don't create enough of a change in the magnetic field. as far as a sensor accross the stop that senses light, i've heard of that too..but personal observation (and flashing lights) suggests that not all lights are set up like that.

anyways, that's what my physics professor said...but he explained it much better, and much more educationally (obviously)

[Napoleon54]

Originally posted by g222leav
according to my physics professor...

there are metal plates or something embedded in the ground at the stop light...when a large metal object (like a car) passes over it, and stops above it, the car changes the magnetic field of the metal plates...this sends a signal to a control box on the corner (you've probably seen this)...the signal tells the the lights to change. this is probably why most motorcyclists have notice why when they're at a light, it won't change for them...cause they don't create enough of a change in the magnetic field. as far as a sensor accross the stop that senses light, i've heard of that too..but personal observation (and flashing lights) suggests that not all lights are set up like that.

anyways, that's what my physics professor said...but he explained it much better, and much more educationally (obviously)

Well said. The switch is basically a magnetic sensor under the pavement that detects your vehicle. Next time you stop at a light, you should be able to see where the pavement has been cut away to install the sensors. (assuming the road hasn't been repaved)

A lot of automatic gates and fences work by the same mechanism. An easy way to get into a fenced-in parking area is to slide something metallic (like a large piece of pipe) under the exit gate to trip the sensor.

[irwin]

Originally posted by g222leav
according to my physics professor...

there are metal plates or something embedded in the ground at the stop light...when a large metal object (like a car) passes over it, and stops above it, the car changes the magnetic field of the metal plates...this sends a signal to a control box on the corner (you've probably seen this)...the signal tells the the lights to change. this is probably why most motorcyclists have notice why when they're at a light, it won't change for them...cause they don't create enough of a change in the magnetic field. as far as a sensor accross the stop that senses light, i've heard of that too..but personal observation (and flashing lights) suggests that not all lights are set up like that.

anyways, that's what my physics professor said...but he explained it much better, and much more educationally (obviously)

I thought it was just the weight that was put on the plate. :confused:

[dbax791]

Bah! My old CRX would NEVER trigger the stoplight switch :angry: Maybe cuz it was made of plastic? :D

[g222leav]

Originally posted by Napoleon54


Well said. The switch is basically a magnetic sensor under the pavement that detects your vehicle. Next time you stop at a light, you should be able to see where the pavement has been cut away to install the sensors. (assuming the road hasn't been repaved)

A lot of automatic gates and fences work by the same mechanism. An easy way to get into a fenced-in parking area is to slide something metallic (like a large piece of pipe) under the exit gate to trip the sensor.

YES YES YES...i am intelligent...and i did learn something in college.

the funny thing is that he didn't even teach us that as part of the lesson...it was one of those side-tracked thing that professors do during lectures...

he was cool, he looked like doc from back to the future, and he taught just like dick soloman from 3rd rock.

[coleslaw]

Originally posted by passwird


I thought it was just the weight that was put on the plate.I think passwird is right. I believe that there is a parallel-plate capacitor that acts as a pressure sensor in the road. Ultimately, the magnetic field within the capacitor is changed by the decrease in separation distance. Many times you will see a sign beside a stop-light line that says "Stop here to trigger light" with an arrow pointing to the line. Many times, though, the lights are probably timed for the expected traffic flow for that time of day. No sensors are used.

[nomoney]

Because that system costs alot, they are starting to use cameras to trigger the lights. This also solves the CRX problem....as well as the motorcycle one. They just did this in my town and everyone tripped out cuz they thought we were getting the red light cameras.

[Nanotech9]

yeah - i hate pulling up to a left turn light on the bike at night... i've sat at them for 7 or 8 mins before, while the other lights turn green about 10 times... finally i just go through a red light.

i SWEAR, if i ever get pulled over, i'll take it to court and claim discrimination and maybe get them to turn up the sensitivity on the sensors dammit.

[Napoleon54]

Originally posted by coleslaw
I think passwird is right. I believe that there is a parallel-plate capacitor that acts as a pressure sensor in the road. Ultimately, the magnetic field within the capacitor is changed by the decrease in separation distance. Many times you will see a sign beside a stop-light line that says "Stop here to trigger light" with an arrow pointing to the line. Many times, though, the lights are probably timed for the expected traffic flow for that time of day. No sensors are used.

And the answer is: http://www.howstuffworks.com/question234.htm

Magnetic sensor (inductive loop) is much simpler, no moving parts.

[coleslaw]

Well I'll be danged. Magnetic coupling. Interesting.

[g222leav]

Originally posted by Nanotech9
yeah - i hate pulling up to a left turn light on the bike at night... i've sat at them for 7 or 8 mins before, while the other lights turn green about 10 times... finally i just go through a red light.

i SWEAR, if i ever get pulled over, i'll take it to court and claim discrimination and maybe get them to turn up the sensitivity on the sensors dammit.

same thing happens to my buddy on his gixxer

[g222leav]

Originally posted by coleslaw
Well I'll be danged. Magnetic coupling. Interesting.

so was i right? or was the other asian right?

hehe...i'm so racist

[Napoleon54]

Originally posted by g222leav


so was i right? or was the other asian right?

hehe...i'm so racist

you were right :thumbup:

[g222leav]

yea dogg....

now, all i need is a bike

[Ladogaboy]

Electricity.

[Speedfreak]

There a little trolls in them. That is where the ones from G|A? are sent. There are tolls from boards all around the world controlling those traffic lights.

[sbp]

Seeing how stupid most trolls are, putting them in charge of traffic lights would be too much.

[Merlin]

The above explanations are fine and all if you live in a place where people actually care about the roads. Now here in the deep South, sensors? We don't need no stinking sensors! Just keep them all on fixed timing. Miss Daisy ain't in that much of a hurry that we need efficient traffic flow. :mad2:

[WhiskeyPapa]

Originally posted by Nanotech9
yeah - i hate pulling up to a left turn light on the bike at night... i've sat at them for 7 or 8 mins before, while the other lights turn green about 10 times... finally i just go through a red light.
A bill was introduced in the Minnesota legislature this year to allow motorcyclists to make a left turn on a red light, as long as the intersection is clear. I haven't heard if it made it through.

[whitak24]

a vast majority of lights around here are on timers. some are fixed cycles and others vary based on the time of day.

a few have sensors, but most of them are camera-based. you know their camera-based becuase the camera sits up above the light

[attgig]

the way it works is if it's green, you go.... yellow, you speed up, and red, you stop. :D

anyways, I hate the ones that aren't sensored....busy intersections during the day never use sensors, but just time delay.
the 4 traffic lights getting from my parking lot to the highway are all timers - freakin timers don't know what they're doing...who the hell programs those things~! :angry:

anyways...another thing that pisses me off is when there's a delay in the sensors. it senses you, but it still waits 30 seconds before it changes :(

of course there are those 'devices' that let you have full control of the traffic lights, but they don't exist ;)

[Ladogaboy]

I knew that there was some sort of an advantage to living in a town without any traffic lights! :P

4-way stops all the way! Nano, you'd be out of here in a second.. or would that be a Nano-second? :heh:

Sorry, had to. :D

[Booyamos]

back home for me (Redmond, WA) the lights also have some sort of sensor on the top of them for emergency vehicles, because my friends dad is the fire chief and they have things in the trucks to activate the sensors and turn all the lights green for them. That is why following an ambulance or fire truck gets you good lights...

[faither]

What the hell do I know. I thought they were on timers. Here in NYC, you can see the succession of lights changing up or don the avenues.

[g222leav]

Originally posted by Kacarp
....That is why following an ambulance or fire truck gets you good lights...

are you a lawyer???:heh:

we have that too, those sensors flash a white light, and all the lights turn green, it's pretty cool

[attgig]

Originally posted by g222leav


are you a lawyer???:heh:

we have that too, those sensors flash a white light, and all the lights turn green, it's pretty cool

got|highbeams

I often flash my highbeams when stuck in the middle of the night.

seems to work on some lights, and not at all on others

[brainsmile]

it's in the ground

[Speedfreak]

Two elderly women were out driving in a large car, neither one could hardly see over the dashboard. As they were cruising along, they came to an intersection. The stoplight was red but they went on through.
The woman in the passenger seat thought to herself, “I must be losing it. I could have sworn we just went through a red light!”
After a few more minutes they came to another intersection, the light was red, and again they went right through. This time, the passenger was almost sure that the light had been red, but was also concerned that she might be seeing things. She was getting nervous and decided to pay very close attention. At the next intersection, sure enough, the light was definitely red and they went right through it.
She turned to the other woman and said, “Mildred! Did you know we just ran through three red lights in a row? You could have killed us!”
Mildred turned to her and said, “Oh My Gosh!! Am I driving?”

[NuTs62]

Originally posted by coleslaw
Many times you will see a sign beside a stop-light line that says "Stop here to trigger light" with an arrow pointing to the line. Many times, though, the lights are probably timed for the expected traffic flow for that time of day. No sensors are used.

I've never seen a sign that said that.. nor do i know of any sensor-triggered lights.. the ones i know of in SF are all timed. And certain ones, at around 1AM, depending on the day, will blink yellow.

I've heard from various people that you can flash your lights, when at a red light, to make it change. I've never tried it. I'm sure it wont work on all types of lights.

[Sir_Froggy]

Originally posted by passwird


I thought it was just the weight that was put on the plate. :confused:


i don't think that's completely true, sometimes when i go biking since i go on the road, i pass by this intersection, since i don't like crossing intersections on the actual street i usually turn onto the sidewalk anyway sometimes the lights turn green and there is no car but just me and my bike so i think the magnetic plate thing makes more sense.


a few have sensors, but most of them are camera-based. you know their camera-based becuase the camera sits up above the light

ya i've seen some of those around too whitak..


yes i think that with some lights flashing ur highbeam works, my dad does that at nite sometimes and when we reach the light it turns green

[g222leav]

i think your sig might be to big sir_froggy...just letting you know before the gam gets you...cause they got me before too.

[Grimm]

Originally posted by Speedfreak
Yada yada yada
“Oh My Gosh!! Am I driving?”

ROFLMAO