Hackable sensors not really necessary...
When I was first in Czechoslovakia (it was still Communist then, so before 1989), I noticed that some towns had illuminated speed indicators/signs mounted on poles or street lights at the side of the road. These looked a bit like the speed warning signs we now have (in the UK), but instead of flashing up your speed as a warning, they flashed up the speed you needed to drive at in order to get through the next set of lights on green.
They weren't at every set of lights and, iirc, on the main road of the junction, but they did help because even though you could see that the lights ahead were red, you knew you wouldn't be held up so no need to engine brake, or gently slow down trying to avoid actually coming to a stop.