Efficiency is the best transition fuel

Geoff Styles runs the back-of-the-envelope numbers and surprises himself with the conclusion:

To my surprise, it doesn't require very aggressive assumptions concerning improvements in fuel economy, reductions in vehicle miles traveled, and additional oil supplies to cover the needs of a significantly larger number of cars in the world.

The bulk of the improvement appears to come from improved mileage standards (he imagines 40 mpg in 2020) - with an additional boost from reducing vehicle miles traveled to 9,000/year (versus I'm not sure what today).

As he rightly points out, this should not lull us into complacency with regard to developing new technologies:

So while our transportation energy mix in the next couple of decades is still likely to include a much greater variety of fuels and an increasing penetration of electricity, we should not lose sight of the potential for realistically-achievable fuel economy improvements and non-efficiency conservation--driving personal cars less and relying more on mass transit and electronic trip substitution--to be the most important "transition fuel" in our arsenal, as we reduce our present reliance on oil as we tackle energy security and climate change.

I think this conclusion is spot-on, and kudos to Geoff for running the numbers and his even-handed, open-minded reaction to the results.