how do traffic lights detect cars?

Answer 1

In many cases there are pressure sensor located in the pavement. You might notice they look like a square or rectangular outlines on part of the road right before the painted stop bar.

Answer 2

Some traffic systems do use a simple pressure plate to sense something on the pavement above. That's an older technology that's largely being replaced with the inductive loop, which is a type of electromagnetic field created by a device buried under the road.

Imagine a tire floating vertically in a lake. You only see the top half of it. Substitute energy for the tire, and pavement for the lake, and that's what it looks like. Only this field can be over 10 feet long. invisible, barrel-lying-on-its-side-shaped energy field. The top half of the "tire" is above the pavement. When an object drives on top of this device, it disrupts the electromagnetic field in the air above the road. If the disturbance meets a certain duration and amount, i.e. car-sized or larger, for longer than 2 seconds, a command is sent to the light controller.

Large or busy intersections sometimes use multiple inductive loop sensors in a single lane so they can give priority to which road currently has the heaviest backup. Metro areas use this, in tandem with a remote control computer system, so they can change light durations at certain times of day, or days of the week, or give priority to larger roads, if traffic controllers notice excessive backups or delays forming.

Answer 3

Some have induction loops buried in the road surface, which effectively detect the presence of the metal in a car; you'll often see these because of a sort of angular tar mark on the road. Some have a sensor on top of the light, something akin to a a PIR or movement detector. Some have no detection equipment at all, but either run on a timer or are sequenced from a cctv control room.

Answer 4

If you look at the road the next time you are pulling up to the traffic lights you will see a rectangle a few yards in front of the lights this is a pressure plate and when you go over it it sends a signal to the traffic light sensor managment box that processes all the light at that junction.
You have got some traffic lights though that operate on a timed sequence rather than pressure plates.

Answer 5

Yes. Of course. Theres also been a myth proven that if you stick powerful magnets under a motorcycle, the light will turn green quicker because the cracks where cars stop in front of the light are there for a reason. Under the cracks are where magnetic fields are. Meaning, the more cars the field detects, the faster the light will change. So yes, traffic lights do detect motorcycles xD

Answer 6

The sensors on top of the lights detect emergency vehicles. There are sensors in the road under the waiting cars, at the beginning of the lane. They sense the metal or something in the cars and trigger the signals.

Answer 7

Used to be tubes in the road surface. The wheels pressed them and worked a pressure switch. Now metal detector loops buried in the road surface. Temporary lights and some pedestrian crossings have low power radar to detect moving vehicles.

Answer 8

the loops in the road are not pressure pads but magnetic loops that detect metal objetcs such as most cars i found this out the hard way i own a concept car that runs on fuel cells and is all made out of carbon fiber and fiber glass when i get to one of 6 sets of lights in my town i often get stuck and end up stoping 5 yards before to let the next car through.
hope this helps????

Answer 9

They're usually on a timer. If you count whilst waiting a red light, they usually change every 20 secs. (if two sets are in operation - longer if a more complicated junction. I know I'm sad but I do this just to see if it's the same all over the country and you'll be please to know (or not) that they are! ( I think I need to get a life)

Answer 10

Little sensor thingies on top of the lights.