How do traffic lights know when I am approaching them?

Answer 1

Doesn't it always seem like that. Every light I approach seems to turn yellow just to tempt me to run it. I bet some dude is up in a helicopter messing with us.

Seriously though, if you look carefully where you stop at most intersections, there will be a square etched into the pavement. This is where a coil of wires was embedded into the road. If you know anything about electronics, this coil acts as an inductor and the light's control box senses when your car enters the middle of it (and becomes the "core"). If it's a little car, or you're not parked in the middle of the square, the light will not change (I've had this happen).

They don't use "weight sensors" lmao That would get a little expensive, don't ya think?!

Answer 2

It's amazing how many people actually believe that traffic lights are controlled by 'weight sensors'! Think about it, anything that measures weight (a set of scales for instance) has to MOVE in order to do so. For traffic lights to be controlled by 'weight sensors', the entire road would have to float, like a weighbridge! A totally bizarre notion...

No, traffic lights operate by one of two methods. One is an 'induction loop' (the diamond or rectangular pattern you see in the tarmac as you approach the lights) which runs a very low electrical current around a coil of wire. This causes an electromagnetic field just above the tarmac. A vehicle passing over the loop causes a fluctuation in the field and triggers the lights to change.
As mentioned above, motorcycles often have problems triggering this type of sensor, due to the lower amount of ferrous (magnetic) metal used in motorcycle constrauction.
And how often have you been stuck behind some idiot at a right turn who won't move forward far enough to trigger the right-turn filter?

The other method used is a passive infra-red detector on top of the lights, similar to the ones at the side of the road (or hanging down from motorway bridges) used to monitor traffic flow.

Before the induction loop system, traffic lights used pressure pads across the road (they looked like a pair of very small plastic speed humps, only a couple of inches high). They were filled with hydraulic fluid and as vehicle passed over them, the pressure change would activate the lights.

Very old traffic lights did work on timers, though...

Answer 3

In the UK, most traffic signals have a sensor in the road some distance in advance of the lights. The normal sequence is timer driven.

Some of the older ones only have a timer.

Fire and ambulance emergency response vehicles have a transponder fitted to the vehicle to trigger the lights.

In many urban areas, there are computerised traffic management systems to taper the traffic into and out of congested zones, these use a combinaton of sensors, inductive and otherwise, along with cameras to set the pattern of the lights. Late at night, these can be set to self trigger, hence the lights turn to green as you approach.

Answer 4

Yes. Most traffic lights have small sensors on the top to measure traffic. If there is a large enough gap the lights will change to let the other side change. This is best at night if there is not a lot of traffic. If you approach them slowly they will change when you get close enough.

Answer 5

There's a sensor in them that detects the approaching cars - that's why traffic lights at pedestrian crossings always turn red when there is a lull in traffic, after you have pushed the button to cross the road.

Answer 6

They know when you are in a hurry, but they will let you through if you need to stop and do something at a light. It's freaky, like they are conspiring with the sock thieves to screw with us.

I am assuming you are joking, as in they always turn red just when you get to them, which would be the opposite of the definitions above.

Answer 7

There are multiple options. As has been said before, older signals are timed. Some systems operate off magnetic sensors in the road, some operate off weight. Magnetic are more common of these systems at least in my area. Motorcycles have trouble setting off these because some use high amount of aluminum which reduce weight and have weak magnetic material to sense. The type most common in my area are camera like motion sensors mounted typically on the pole for the traffic signals. Some people misidentify them as red light cameras.

Answer 8

Throughout the day most traffic lights are on timers. After certain hours they use weight sensors in the road to detect when a car has pulled up.

Answer 9

The orbital mind control satilites sense when you are in a hurry and send a signal down to the lights to change to red, so you have to stop.

Answer 10

some of the newer ones work off of sensors in the road,and the older ones was on timers,there automatically timed to change at certain times,but most places now are using the newer type with the sensors in the road,these usually activate about 50 feet before you get to the light,larger cities have switched over to these also good luck hope this helps.