Reverse cruise control

A thought about driving: setting the cruise control on a car is the same as setting a "minimum speed": I can use the gas to go above this speed, but to go slower I have to deactivate the cruise control (via the brake or the switch). Now this is nice and all, but what I would really like is a way to set a maximum speed, on the fly. Because I will often be driving down the road, keeping up with traffic, only to discover that I am going 15-20 miles over the limit, which is a bit too much for my liking (speeding tickets and all that). If I could set my maximum speed to some value, on the fly, then I wouldn't have to keep checking the speedometer. (It would also be useful when driving in stop-and-go traffic, where one's instinctual desire to drive the speed limit results in more frequent stops.)

So here's how it works: you get up to the max speed you want, and then press a button, activating "max speed". Until it's deactivated, the car prevents you from accelerating beyond that speed. The feature can be deactivated either with the switch, or by flooring the gas pedal: the latter device lets you speed up quickly in an emergency.

Auto manufacturers, feel free to implement my idea ASAP. :)