" Why not hook up a small diesel motor to an electric generator, this should result in greater savings since a smaller horsepower motor running at optimal rpms should be more efficient than the current gasoline engines."

That's what's meant by a plug-in hybrid Most use gasoline engines, but a small diesel would be even better. In the US, a mjor problem with diesels is that fuel standards are too slack to permit use of some of the newer low-emission diesels.

One problem that's not discussed enough is the environmental cost of supplying electricity to plug0ins or all-electric vehicles. The electric motors don't pollute, but most power plants certainly do--most run on coal, and run at a low efficiency at that.