I would to call your attention to a study which was conducted by the Pacific Northwest National Laboratory which is operated by Battelle for the US Department of Energy.
Please take a look at “Mileage from Megawatts“.
In short, what this study found was that surplus electricity generation and storage capacity if used in plug-in hybrid vehicles, could power 87% of our vehicles. Given that plug-in hybrid technology is something that we can do today this offers a substantial opportunity to reduce our dependency on foreign oil since 73% of our oil demand is caused by gasoline consumption.
In the east and mid-west, 100% of the vehicles could be powered entirely by surplus electrical generation and distribution capacity. Only in the Pacific Northwest is this not the case. However, if we were to add wind generation capacity this could be addressed as well. Unfortunately, the very best lands for wind power generation are presently owned by the federal government and not near transmission facilities, this being the eastern ridge of the Yakima valley which has very constant winds ideal for power generation.