Plymouth Voyager III Concept
The Plymouth Voyager 3 was a minivan concept car revealed in 1989. Part of the car's aerodynamic design featured a glass roof. One thing that was unique about this car was that in a sense it was a miniature tractor-trailer; the cab separated from the back of the car and could be driven by itself. The rear wheels of the cab were hidden (notice on image) when it was all in one piece.
Source: Wikipedia, 2013