The Opel Twin articulated a staggering proposition which, for 1992, was considerably ahead of its time. Highlights of the Twin concept car included interchangeable drive units, with the engine, transmission, rear axle, and energy accumulator housed inside. This allowed the vehicle to run on whichever drive assembly made the most environmental and economic sense.
For highway driving, for instance, there was a three-cylinder gasoline engine (0.8 liters, 34 hp), and for city or short distance driving, an electric unit with two wheel-hub motors (each with 14 hp). Arranging all the drive assemblies in the rear allowed for a variation to the usual seating layout. Instead of sitting front left, the driver had a central single-seat position, while three more passengers could sit in the back.
Source: Simon Hacker/MSN Cars; www.carbodydesign.com