Sensors are common, ranging from basic induction loops in the road to microphone arrays that can tell you what type of vehicle is on each page of an intersectio

Sensors are common, ranging from basic induction loops in the road to microphone arrays that can tell you what type of vehicle is on each page of an intersection from the tire noise. Sadly there are laws that require each light to be green for a minimum period, so all these really do is keep one phase of lights on longer at rush hour.