How do traffic lights operate?
Neesha: Modern traffic signals are typically operated by a computer controller mounted near the signaled intersection. These controllers can be programmed for each day of the year, for different times of the day, and can be actuated by sensors at the intersection. Typical sensors include ultrasonic motion detectors mounted on signal cross arms and wire loops buried in the street. Controllers can also be operated from a remote traffic center or by a computer that is programmed to optimize signal operation based on input from sensors at a group of intersections. Traffic signals are typically programmed based on traffic studies that determine the number of traffic movements through the intersection. Heavier traffic directions may be programmed to receive longer green signal times, or for coordination with signals downstream. Signals can be programmed for late night operation in different ways. One way is to have the principal or more traveled road given a green signal by default; a vehicl
