Could the car be controlled by some kind of propulsion system?
Small jets or propellers? But then that would add weight and need energy. The retractable wheels make sense. Thanks!
I think it would be easier to just use the wheels to get to highway speeds and then retract. When exiting highway, once you slow down the wheels go down and you run on those.
The highway system uses magnetic propulsion to keep your speed constant and controlled.
Jets and propellers would probably be too complicated and slow to respond in emergency. Also very energy in-efficient.