[Schroedingersat]

Bit of a non-sequitur, but the easiest way to implement such a speed limiter is to make it such that the car won't accelerate when over the limited speed (and either warn the driver or reduce power gradually so it slows down gently) without manual intervention, rather than jamming on the brakes

[adhesive_wombat]

That's how my old car does it, but the new one will downshift if it wants to slow down a lot (either if you reduce the cruise speed a lot, or it imagines it saw a lower speed limit sign). Seems dangerous.

[Epa095]

That's how my cruise controll works. It don't really work downhill;-)