The Ford Seattle-ite XXI was a 3/8 scale concept car designed by Alex Tremulis and displayed on 20 April 1962 on the Ford stand at the Seattle World's Fair.
[1][2] The car contained novel ideas that have since become reality: interchangeable fuel cell power units; interchangeable bodies; interactive computer navigation, mapping, and auto information systems; and four driving and steering wheels.
[3] The concept of some form of compact nuclear propulsion device was included as a possible power source on the assumption that radiation issues could be overcome without the need for prohibitively bulky shielding.
The designers determined the six-wheel concept would enhance tracking, traction, and braking.
It had an interchangeable front-powered section that enabled the car to be turned into either an economical city runabout or, when needed, a powerful transcontinental cruiser.