Wouldn't that be annoying. Like as if people don't know when they're breaking the speed limit.

Maybe a 10-over alarm would be better.

People would disconnect it.

There is some merit in the idea if one considers that populated areas have much lower limits than highways and the signage in many populated areas is either missing or obscure. It would require considerable integration of where the limits change from one area to another and probably prove too expensive to implement.

My grandfather's 1962 Buick had a needle that could be adjusted on the speedometer. If the speedometer needle went past the "set" needle a buzzer went off. Us kids thought it was pretty damn cool that a buzzer went off every time the car went over 25 or 30, which is where he set it when we were riding with him in town. Grandpa set the needle for about 100 mph the rest of the time.

My sister bought the car from him in 1979. I noted at the time that while the car had all sorts of interesting gadgets it did not have cruise control.