Oh, I'm sure most people would agree with you, and the idea is kind of out there, but I'm sort of serious. In fact, it seems kind of insane to me that this isn'

Oh, I'm sure most people would agree with you, and the idea is kind of out there, but I'm sort of serious. In fact, it seems kind of insane to me that this isn't the status quo already, the technology has been there for a decade or more. I think that's when I first drove a car that had a warning light go off when I exceeded the limit, and I remember thinking "why is it even letting me drive this fast?". I'm less sure about the red lights, which requires technology beyond static maps and GPS, the kind of technology required for true autonomous driving (which incidentally will also respect the speed limit). We have as a society decided we don't want people to drive faster than a sensibly derived speed, we already license cars to be road legal or not, and exact positioning is already utterly ubiquitous, put those things together and you have pretty much solved the problem of speeding. The only major issue is GPS accuracy -- e.g. what if on the highway your car thinks it's on a parallel slow-moving road. But you don't need perfect accuracy, you only need a reasonably accurate measure of inaccuracy and a fallback to the higher limit (or no limit). The other major issue (and the reason why this won't happen anytime soon) is current car drivers being uncomfortable with their own property limiting their capability to drive beyond the speed limit, which most of them do as a matter of course, to which I say, tough luck, you're free to drive a non-limited car on private ground. Note that none of this involves any central tracking of cars, in fact it's less invasive than the current system of monitoring using radar and cameras.