my thoughts are: low mass vehicles - if you use something like carbon fibre rather than steel (which the Rocky Mountain institute proposed).

combined with some kind of plug-in serial hybrid engine like the Volt-
which would use a small ICE engine to charge a battery.

But then the battery technology still has to improve.

As for the fuel, bio-diesel from Algae may be the best option as a renewable carbon-neutral fuel. Since algae can be grown in non-arable land - even in seawater and can produce orders of magnitude more oil per acre than say say canola, or soybean. Its not there yet but is doable.

on a slightly different tack though why not work toward developing
PRT systems, personal rapid transit in densely populated cities.
see this link here


The problem with changing the transportation industry from gas to electric is that this will not do anything to alleviate the traffic density problem of adding thousands of cars to a city each year.

On the other hand if you have a grid network of stations of elevated (very light) rail electric powered pods (made for 3-4people) which could take you anywhere on the grid directly without stopping, it might just displace the need for cars for much of the population.