You can see filled-in grooves in the concrete at many intersections, where a coil has been embedded in the asphalt. It’s an inductive coil, sensing the presence of a big hunk of metal (read: “car”) which may be used as an input. At the last stop light before my office, there’s a coil, and sometimes when people don’t pull up to the crosswalk, the light doesn’t trigger. I’ve had to wait for a few turns of the light a few times, gently honking (read: “being the asshole”) to get the first car to pull up to the proper position to trip the sensor.
