@sooperdooperroofer @mondoman712 Modern petrol cars contain lots of computers too.
Automatic enforcement, with the right to override it recorded in the black box to be used as evidence in crash cases, is a perfectly reasonable idea. But inevitably there will be bugs, just as there are in self-driving cars (especially the often dangerous "semi-autonomous" vehicles).
However there is a cheaper solution: Fixed, widespread speed cameras. Which right now are effectively banned in the UK, because the treasury confiscates the fines (local government pays the running costs, and therefore can't afford to run any).
While I understand there are usability issues, and design can help with that, if you're not able to drive your ton of metal safely and legally you shouldn't be driving it. If people expected to get caught, they'd drive slower.
The bottom line is speed limits are the law. And lower speed limits reduce the number of serious injuries dramatically and help to push people onto public transport. Although with old cars they increase emissions slightly; with modern hybrids they reduce them.