Of necessity we will have a mix of vehicles. As posted by others, city and short distance commuter cars can be electric or plug-in hybrids. Highway vehicles will be hybrid gas or diesel, or later on fuel cells powered by hydrogen, or natural gas in the interim.
Electricity will come from a mix of sources; hydro, clean coal, nuclear, wind, solar, geothermal and combined cycle gas power.
The fuel on board in the interim will likely be a selection of gasoline, diesel, ethanol from algea or cellulose, compressed natural gas (synthesized from coal or LNG from overseas), and hydrogen for fuel cell vehicles.
In other words, the car of the future will not look all that different, but the “gas” stations will have plug-ins, ethanol, gasahol, diesel, hydrogen, and compressed natural gas.
Tom & Ray, we will need a variety of energy sources and the vehicles will also have a variety of propulsion sytems and fuels. I believe all in ternal combustion engine-powered vehicles will be hybrids in the future.
Energy independence will still be an issue, since the US consumes far more energy than it produces. Turning the vast US coal reserves into clean energy will go a long way.