When General Motors rolled out its "skateboard" vision for a fuel cell car at the 2002 Detroit auto show in January, there was buzz, and there was a big question. The skateboard concept, called Auto-nomy, was the product of GM's Design and Technology Fusion Group, and it radically reordered automobile physiology: Fuel cells, hydrogen, motor, and brakes were all crammed into a 15-foot-long, 6-inch-thick chassis onto which modular car bodies could be snapped. Drive-by-wire controls would plug into the skateboard's computer brain through a docking port.