speed regulator

My idea would be to implement in all vehicles, a regulator/sensor that would control the speed of the car. A gps can pick up the speed limits, why not have a sensor such as that, keeping the vehicle from going more  than 5 miles over that posted limit. Limits are posted for a reason, safety. There is NO reason why a vehicle should be driven 100 or 130 mph. With all the technology today, I am sure this could be developed and keep people safe.