We (Racelogic) designed a GPS based system for Palmer that uses a GPS map of the track and basestation corrections for 20cm accuracy to predict where the car will be a few samples down the line based on its speed, heading, radius of turn, and the known limitations of the car it is fitted to. If the system predicts that the driver is coming into a corner to 'hot', or accelerating to early then it removes power to stop the car going off the circuit. It also limits speed in the pits, and if the driver goes off the circuit it applies a speed limiter.
Fitting this system to twenty or so cars at Palmer is justified financially by saving just one of them from damage at the hands of a punter, but the limits are such that if you are getting things right then there is NO intervention.
With more and more birds in the sky; the Russians launched 6 more GLONASS sats just recently, Galileo (supposedly) launching for operation in 2012, and the Chinese COMPASS (or Beidou-2) system hot on it's heels; the accuracy of GNS receivers will get better and urban situations will become less problematic. This kind of technology will inevitably reach the consumor car market, and most likely as a safety requirement. putting a 60 limit on a road doesn't mean to can drive 60 along its length, but not everyone is switched on enough to realise this. Dynamic speed limits are the way forward.
As for the traffic light senario. it is easy enough to prevent someone from moving in a local system if they are in the box queing at a red light, cross the line and the car stops, no accident...
