Here's a really wacky postwar concept. The 1959 Cadillac Cyclone was chock full of gadgets that were never put into production, like the bubble roof, and other gadgets that never even worked on the concept like the two-speed rear end and the "radar" in the nose cones.
It probably worked as well as the Mercedes system.front cones masked radar devices allowing the car to steer itself thanks to a tracking sensor placed under the front of the car that could follow a signal from a wire imbedded in the road; a test loop was set up at proving grounds to show the effectiveness of the system. A proximity warning device was supposed to prevent collisions but it was never tested in practice.
Very informative site about the Cyclone: http://www.car-nection.com/yann/Dbas_txt/Drm_cycl.htm