Cruise control that guides you towards a speed rather than setting it absolutely
Problem: Cruise control in cars is a switch. It’s awkward and jerky to reduce speed or get back up to cruise speed.
Solution: A cruise control that doesn’t actually set speed, but instead makes the accelerator pedal stiffer or looser such that leaving a foot resting on the pedal will cause the car to go at cruise speed. When at the right speed, the pedal is stiff to push down but very light to release. When above cruise speed the pedal starts to push back, and when below it the pedal becomes easier to press further down. You can now get a feel for the cruise speed you set, without that car controlling the throttle.