Airbus has a futuristic modular concept involving a passenger capsule that can be detached from the road-going chassis and picked up by a helicopter-type machine.

The experience of the DARPA challenge has shown that dealing with road junctions and traffic queues in cities is becoming possible too, especially with advances in machine vision.

No giant sucking sound, just the gentle hissing of an inner tube losing air, threatening a flat tire that could send the American dream machine off the road.