system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5 Why can't traffic lights be designed so that autos aren't stuck at red lights when there is no traffic approaching the green lights?

Strings of cars idling at red lights, adding pollution, wasting fuel and time when no traffic is approaching the green light. Some side streets apparently have sensors that trip the light, so a steady flow of traffic is immediately stopped so that one car doesn't have to wait. Why can't traffic lights on main strips be engineered so that we aren't stuck at red lights when no traffic is approaching the green? Why are sensors placed to stop a dozen moving cars so that a single car on a side street gets an immediate green? Living in a big city with heavy traffic, this is maddening and never made sense to me. Please explain it like I'm five.
gpt
Many are. There are ones that have sensors which need to be triggered to begin the cycle of switching from red to green, say exiting a busy parking lot. During business hours, you need the light, but when the businesses are closed, no point in stopping traffic on the road.