GPS isn't good enough for that yet. I have received warnings from my GPS because it thought I was driving at 70 mph in a 20 mph limit. In fact, I was driving at

GPS isn't good enough for that yet. I have received warnings from my GPS because it thought I was driving at 70 mph in a 20 mph limit. In fact, I was driving at 70 mph on a motorway flyover above a residential street that had a 20 mph limit. If it had been able to cut the engine (or, worse, apply the brakes) then that could have produced a dangerous situation.