Many years ago I was surprised to find out how traffic-detecting intersection lights worked.
I assumed computer vision had been solved and they had reliable enough detection of cars, so you could just plop a few cameras in the intersection to detect waiting cars and start the transition when safe.
Nope! Instead, large numbers of intersections are dug up and electromagnets are installed to detect cars. These are very sensitive (but can miss cyclists) and super-simple; a microcontroller can reliably detect a car as a pulse on a line.
I assumed computer vision had been solved and they had reliable enough detection of cars, so you could just plop a few cameras in the intersection to detect waiting cars and start the transition when safe.
Nope! Instead, large numbers of intersections are dug up and electromagnets are installed to detect cars. These are very sensitive (but can miss cyclists) and super-simple; a microcontroller can reliably detect a car as a pulse on a line.