stop lights....are they on a timer? are they equipt with sensors?

Question

is there a sensor to detect how heavy the traffic is...

is there a sensor to know is a vehicle has approached a stop light, how long it will stay red....

Answer 1

A definitive yes

Signalized intersections are controlled by a variety of things

1) Manual triggers (lights are always green until a pedestrian pushes a button to cross the street or a car rolls up on a pressure pad - this last one is pretty old..they required too much maint. and were phased out)

2) Induction loops: Wires buried in the pavement sense a large iron mass (a car) and trigger - you find these in left turn lanes a lot.

3) Infra red sensors (usually mounted on the traffic light - they look like cameras). The heat from the car triggers the signal. Same thing with motion sensors.

4) Coded signals.. similiar to #3 but these are triggered by special events. Police cars, busses, ambulances, etc.. have transmitters that overright the traffic light system and give a green to the oncomming vehicle (or reds all the way around)

5) And lastly.. just plain old timers....

does that help...

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Answer 2

Yes ... and No .... and maybe.
It depends on where you live and what the local city coucil wants. In New Zealand the city I was in had detectors under the road, the traffic light people said they were like the old fashioned mine detectors. You could actually see where they were placed under the road. Generally they had two detectors per lane, just before the traffic lights / intersection, and another about 50 meters / yards before the lights. If you look at the tarseal you will see a black square or black square figure of eight (sideways) where the traffic light people cut into the tarseal, put in the wires, and then filled the top.
Now, just to make it more complex, the traffic lights are controlled by a computer on the side of the road by the lights, and it is linked to a central computer.
At night the lights have a preference, so drunk / sleepy drivers
are given a green light. If a car arrives at a red light the detector changes the other lights to red and gives the green to the waiting car.
During the day the lights cycle, but the city council controls the length of the cycle, and the individual phases. So, for example, a busy road with a side street, the busy road will get most of the green, and the side street only a short green. I think the average cycle was about 1:30 minutes.
But, they could adjust the phasing so, for example, a sports event, they will change the phasing when just befor the end of the game, so all the main intersections leading away from the stadium will give a very long green to the cars departing the stadium area.
During the day, the traffic is monitored and if too many cars go along a road, they will reduce the green cycle and increase the red. Also, certain vehicles, e.g. buses (Now, how would I know that!) can have a special device fitted which enables the green light to hold longer until the bus has entered the intersection. This reduces running times by about 5 to 10 minutes in an hour.
So that was the "Yes" bit. Now for the maybe.
If the link breaks down / fails, the traffic lights loose their iniative and do what is called "autocycle" where they go onto a fixed cycle. This means no constant green in the early hours of the morning for drunks / sleepy drivers, no priority for buses, etc.
And the "No" bit? Well, that's what happens if the city council isn't prepared to spend any money, yeah, they have them in New Zealand too.
I'm in China but haven't paid to much time to the lights.

Answer 3

Yes to both questions: A lot of stop lights are on timers. But more and more they are moving toward putting them on sensors so the lights will stay green on the busy (main streets) if no traffic is on the smaller roads crossing the main streets.

And now they are even installing cameras that take your picture and automatically sends you a ticket if you run a red light.

Answer 4

Some traffic lights are on timers (which are annoying). Others have sensors that detect that a car has approached the intersection.

Answer 5

they have a sensor and a timer. if u look closely on the pavement u'll see a round blk circle that is a sensor that detects the heat of the car and turns green. every so often the timer changes the light to red. so if u stay on the big blk circle and the timer is at the set time it will change color to green.

Answer 6

it depends. In a small city where ther is lesss traffic, stoplights have a sensor that detect when a car comes to the stoplight, and it turns into green. But in a crowded big city, where there s always traffic, the stoplights have timers. Visit this link for more information: http://auto.howstuffworks.com/question234.htm

Answer 7

hay you ever noticed when you stop at a light the tar stuff on the ground right before the limit line well thats the sencor its just a huge magnet that is in the ground the metal of your car trips it. sooo sometimes it doesnt get triped and you end up stuck there all day lol but yeah its on a timer during the day and then the sencer at night time

Answer 8

it depends, i think that the stop lights are programmed to blink a certain light at a certain times because it turns red even when there is only one car on the other side. i heard of some that may be on sensors, the high tech ones, instead of lights, they use pictures and lights to tell what kind of vehicle should go and when.

Answer 9

Stop lights are set on a timer and they are not equipt with sensors

Answer 10

There are sensors under the road that magnetically check how many cars there are. They are run by a computer system that (in theory) maximizes the number of cars pre light.