I don’t understand how they work, what they’re hooked up to and how they know when to turn from green, to yellow, to red. Are they timed? Is there a sensor, perhaps a small man hiding in the pole controlling it?
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It varies wildly from city to city and intersection to intersection.
For starters, there’s almost always either a preferred direction or a timer. Let’s say you’re on a small rarely used 2 lane country road and you hit a 4 lane road down a rural town. It makes more sense for the people who travel on the main road to go through by default unless someone’s trying to make a left turn right? Well there will be some kind of sensor monitoring the smaller road if anyone gets there, otherwise it defaults to the main road.
What sensor you asked? Again, different types. There are pressure sensors for the weight of the car but these are rare. There are cameras that can detect a car in a specific lane, those are getting more common but not the most widespread yet. The most common right now is a loop of wire that sits under the road and detects a magnetic signal from your car driving over it. Any of those attaches to some control box.
Now in a major city, it’s more likely to have something timed in a way that the city decides it’s “fair” OR they connect the boxes and have some kind of algorithm decide which light to turn on when to get the most people as possible to their destination ASAP, and avoid anyone waiting for too long. This is a thing, but isn’t super common outside of major cities.
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