Intelligent cruise control for cars

There are millions of inventions out there for cars, so just sticking this out there. Cruise control has been around for years, but I don't this it's that efficient. A more intelligent system would be to give a +/- speed margin of flexibility and the car uses gravity to accelerate to the max when going downhill, and eases slightly on the throttle to minimize laboring when going uphill. GPS information might maximize efficiency further.