"Matt Barrow" wrote

Most (not all, but most) of the sensors you speak of are for allowing the
passage of emergency vehicles, not for determining traffic flows. Most
communities don't even have those.

Are you kidding me? NC seems to love the "trip light" concept. Does it
make sense? No. Do they use it at almost every intersection, even 4 lane
highways? Yes.

On a highway between Lenoir and Hickory NC, the lights are all on trip
sensors. It is nearly impossible to go from one town to the other in
daylight hours, without being stopped by at least 3/4ths of the lights.
They are going to have to widen it to 6 lanes. (under planning now) If they
would time the lights so traffic could flow, they could put off widening for
at least 5 years.

By the way, mostly they are magnetic loop type, pavement embedded wires.
--
Jim in NC