The coming decline in oil supplies as well as concerns about global warming demand vehicles that use much less gasoline or diesel than conventional vehicles. Plug-in hybrids can be powered either by an internal combustion engine or by batteries feeding electric motors. The batteries can be charged either by the engine when the vehicle is moving or by an external electrical source when it is parked. Since most trips are shorter than the electric-only range of proposed hybrids, the gasoline engine would be used relatively rarely. The technology is an interim solution ...