I often cycle around the city, and sometimes when I need to turn left and I am the only thing in the left-turn lane, the intersection infrastructure senses that I am there and triggers the left turn arrow.
At some busy intersections that can have a long left-turn lane, there is even a sensor to sense how many people are trying to turn left and will adjust the length of the light based on this. Where are these sensors and how do they work?
In: Engineering
There are a few ways. Induction loops cut into the pavement to sense steel cars is the most common, but it’s going the way of the dodo with newer technology, like microwave, radar, and video detection taking its place. Pedestrians and cyclists are picked up using the newer stuff, which can distinguish between cars and people.
In longer turn lanes (and on higher speed through lanes) there is often a sensor placed well in advance of the intersection for two reasons: the controller can add time to a signal phase if it detects a long queue of cars, and it can add a few seconds if a vehicle arrives just before it was about to go red.
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