Most signals do not have sensors on them to see gaps…
They are set to timers, depending on the time of day, amount of traffic yadayadayada
back in my architecture days i took an urban planning class and they went thruogh and descriebd how the system works…and how much it costs to have a study done to see if an intersection needs more time, an arrow or whatever
they also found that decreasing the amount of time a signal stayed actually increased traffic flow and made people happier. Instead of sitting around for 3 minutes (which seems like an eternity) they would have it at 2 mins or less maybe less cars went through per cycle but overall more traffic moved, and because people were moving forward regularly instead of just sitting and sitting they were happier