[catalogia]

I'm not sure why you've been downvoted. Traffic-aware traffic lights are generally implemented using induction loops built into the road surface: https://en.wikipedia.org/wiki/Induction_loop

Today, many have cameras for other reasons. But this is not ubiquitous and the prevalence of these cameras varies from location to location. Many traffic lights don't have cameras (many don't even have induction loops, and work off timers instead.)

[nucleardog]

In areas where the ground is covered in a foot of snow and ice all year those aren't particularly effective and they do use devices that look kinda like cameras and everyone assumes are cameras.

They're actually just small radar devices. It's a much simpler problem to solve across a wide variety of conditions to simply point radar at the ground and when the distance suddenly drops 4-8' assume a vehicle is there.

These devices don't have any sort of lens assembly which should be your first clue, but they also are pretty easily differentiated if you own a radar detector as well...