Neil and Gabriel have given us some insight, and here is my two paise
worth of an addition!
Here in Melbourne, traffic lights are also controlled by magnetic
sensors which are placed under the road, just before the white stopping
line. When there is a slack in traffic, say in the night or during off
peak times, then we find the green signal lit up on the main
thoroughfare. Should a vehicle come up facing a red light, no sooner
the vehicle comes over the sensor, then the lights automatically change
to green, and then revert back as they were. The advantage here is that
unlike the 'timer' system, traffic flows smoothly during slack times.
During peak times, the timers overide the sensors, and each side gets
equal time to cross at the junctions.
There have been many times when the Government in Goa have invested in
traffic lights, only to have them go out of order in a short time, and
then they have remained standing till another new system is installed
with the same fate and result. Maybe it would be a better idea if the
government does a proper study about the quality of they system they are
introducing, and have a sort of a service contract with the supplier to
maintain the system, with penalities.
