Interesting Things with JC #239: "Traffic Lights" - Most common traffic lights operate based on timers. In areas that are not as congested, timers are not the best idea, as rural drivers may be sitting at a red light for an extended period of time. This is where sensor based traffic lights are more of an advantage. The actual sensors used can vary greatly per location, they could be lasers, rubber hoses filled with air, video cameras or inductive loops.