Make the auto-pilot on cars that will stay in a highway lane, maintain the speed limit, slow down to not hit the car in front. The car would have a bar code scanner that would read the signs and notify the driver of such things as upcoming exits or speed changes.

All this technology is currently available. The signs would have to be upgraded and the lane lines would need to be maintained.

There might need to be a dedicated lane for this. Like the HOV lane.

When a driver wanted to take advantage of this they would merge into the AutoLane turn on their autopilot and set their exit.