Traffic Light Sensors: How do they work?

June 29 2017, Applewood Kia Langley

Traffic Light Sensors: How do they work?

The bane of many, traffic lights are a staple part of the modern driving experience and act as electronic guides which, collectively, direct and negotiate traffic through our cities, across our highways, and out across the world. If you were anything like me then when you were young you liked to imagine that these colourful shapes could be manipulated by some near-mystical countdown clock or argued with until they change to the only colour that really matters for a person at a light – Green.

Now, I know that’s pretty ridiculous but the fact of the matter is, when you eventually get behind the steering wheel and head out in your car there are few experiences that can be as aggravating as coming to a red light whether you’re in a hurry or not.

That’s driving life, though.

Traffic lights are just a matter of fact. They’re inevitable. These sentinels keep us from pure navigational anarchy and since the first models were installed beginning on August 5th, 1914 on the corner of East 105th Street and Euclid Avenue in Cleveland, Ohio.

But REALLY - how do they work?

Right off the bat it’s probably worth mentioning that if you’re one of the lightweights on the street – a scooter, motorcycle, or comically small car then you’ve probably had your share of experiences waiting – and waiting, and… more waiting at lights.

Sadly, this is to be expected if you’re dealing with one of these colourful multi-eyed monsters.  

There are a few ‘types’ of traffic sensors and unless you know specifically which one you’re dealing with it can be difficult to recognize the differences. I’ll get you a bit more details when necessary, but to simplify the process I’ll point out that there are two categories of light sensors: Fixed time control, which as you probably realize means that there’s not much you, as a vehicle at the light, can do to make the process more streamlined. Then we have coordinated control, adaptive control, and a number of lesser-used options that are usually installed for specific purposes based on collected traffic data.

Then we have dynamic control light sensors which separate into subcategories.

I know, it’s a little complicated, but we can simplify it further:

In most cases it comes down to what is lying just below the concrete surface. Specifically, there’s a loop of wires nestled under the pavement near the stopping line. These inductive-loop traffic detectors operate by sensing the force and frequency of electromagnetic field over the wires. Put somewhat more simply – if you’re stopped on it, the sensor knows that you’re there.

Smaller vehicles, however, often will not have sufficient conductive material to trigger the system to change the light ‘manually’.

Can I trick the light to change?

Now that’s a pretty interesting question – whether you can do it in a way that isn’t already recognized by the system to work to your advantage is based a bit on what type of sensor you’re dealing with and how it responds.

Effectively, you’re already ‘tricking’ the light to change simply by activating the inductive-loop or one of the other times of traffic sensors, so you could easily argue that this is already happening. Now, that said, some types of traffic lights do have specialty sensor conditions that are aimed at assisting emergency vehicles.

With that information you can understand how I might say that you can, but, hopefully, if you are you’re doing it because you drive one of these emergency vehicles. But given the fact that not all traffic sensors have this feature built into it, well, you might be working against technology without reward.

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