How do traffic lights work?

Question

I have heard that there are sensors in the road, how true is this and please list sources.

I'm not an Idiot I know how they turn Red green and yellow. Stop trying to fill your quota of answers and answer questions seriously please.

Answer 1

How do traffic lights work?

Many street lights are equipped with Traffic Signal Preemption systems like the 3M Opticom or the Tomar Strobecom. These systems enable emergency vehicles to change the traffic signals from Red to Green, and to change the traffic signals for others from Green to Red. This enables emergency vehicles to travel more quickly and more safely.

These systems operate by means of a receiver mounted on the traffic signal and a transmitted mounted inside the emergency vehicle.

The transmitter is an infrared light which is flashed at the receiver. The transmitter inside the vehicle may transmit a low-priority signal (10 Hz) or a high-priority signal (14 Hz).

Answer 2

Some systems do have sensors to determine when cars are approaching an intersection. If a minor road intersects a major road, these systems usually keep traffic moving on the main road unless there are actually cars coming up to the intersection on the other street, so the main traffic doesn't have to stop for no reason. Others are set on a timer and the amount of traffic has no bearing on when the lights change.

Answer 3

It used to be that stoplights were purely mechanical switch timers. Then with the advent of the microcomputer, they could do more things to change the fixed sequence.. They could adjust the timing sequence to favor one direction during rush hour for example, simply by making the microcontroller know the time of day. And then they added sensors to alter things like left turn lanes, so a left turn did not enter the sequence unless a car was there. The first sensors for this were simply a photocell which detected a change in the light pattern in the first spot in the lane, then they went to ultrasonic sound (on lanes with a center island) and sensed the reflected sound from a vehicle, and now they use magnetic loops under the pavement which sense the change in the Earth's magnet field the steel makes from your car passing over the loop. Watch for loop marks in the pavement. If a loop needs replacement after being paved over or if the decide to add a loop sensor to the control, they cut a loop shaped slot to lay the wire in and then fill the slot with tar. They are immediately obvious if you are looking for them. Now, they have gotten even smarter, linking a series of lights so they can sequence whole streets so traffic moves more smoothly over a much wider area, especially during rush hour. You can see this for yourself. On a street where you can see several lights (I hear New York is really good for this with short blocks and straight streets), just watch. If they are linked, they will all turn green insequence as a group, like dominos falling. Most every light these days is a "smart" light which senses traffic and adjusts itself to accomodate special cases, such as left turn lanes and favoring one direction. Have you noticed the incandescent lamps are being replaced with huge banks of LED's? The LED's take 1/10th of the power of the old filament bulbs and don't burn out. A typical LED will last 100,000 hours, while the old incandescent lights ran about 5,000 hours. Cost is about 2-3 times the filament bulbs, so that means they will pay for themselves in a single replacement between the cost of the bulb and the saving in electricity.

Answer 4

It depends on the intersection. Most of the ones in my area have magnetic plating in the ground. We test them by running shovels along the ground. Those lights can be programmed for a time loop as well, but most of the time the traffic is not heavy enough to do that. Some lights do have optical sensors, but from what I've heard they are not accurate and easy to mess with. I know that police lights are set at an angle and frequency that changes the light in their favor if they are running code, I'm just not sure of the specifics.

Answer 5

The sensors in the road are called 'inductive loops.' They are actually electromagnets designed to sense iron. When enough iron is inside the loop's field to raise the attached henry meter to a predetermined level, the light's cycle initiates. It is estimated that over 90% of the traffic signals use inductive loop technology -since the 1960's. Check out the link below for many more details. I use their product on my motorcycles - awesome!

Answer 6

well i heard it in a different way is there is main system that controls the timing of the singnals during different times and there are sound sensors i think it works with for ewg when an ambulance turn on its sirence did you ever notice a abmbulance reaches a signal the signal becomes green, i think it has sound sensors because my dad tried honking near the singal and it became green don't try it vbecause it may creat a big prob you might go jail

Answer 7

Usually there are no sensors (unless you live in New York City). It is all on a timer that rotates constantly. If you timed it out on a stopwatch, you could say... ok it spends the first 30 seconds like this, 15 seconds here, 30 seconds like that, and so on (for example). It's up to your city. But, no sensors (usually).

Answer 8

Some have sensors in the road, you can see the lines where they bury the wires. Some have timers. Some are even computerized and keyed to traffic.

Depends on the budget.

Answer 9

Yes. Sensors are used. So are timers in some intersections.

Answer 10

Timed and/or sensors