Interesting, I wanted to do something very similar for red-green stop lights at some intersections ... I just tried using the speed limit signs, as I assumed that they could be connected to circuit network ... but they cant. But seems like a small tweak to speed limits to allow them to read circuit network inputs to set the speed limit would make sense and cover this use case.
I thought about this, and initially assumed it wouldn't be necessary to make speed signs connectable to circuits (actually, i dont know why i came to this conclusion). But demand is there, so i'll fix this issue and change the speed limit signs to allow circuit connection.
