Mr. Lovins, et al make the strong case for light cars in Winning the Oil Endgame. When you consider that less than one percent of the gas you use moves your passengers, or that ninety-nine some odd percent has to move the vehicle, putting cars on a diet makes sense.
What you've gotta love about Lovins and the Rocky Mountain Institute folks is their willingness to go beyond their compelling ivory castle pontifica (buttressed with good, hard science), by developing patented prototypes to further lure some enterprising automaker to a future in plastics.
To date, composites have been cost prohibitive. But with oil prices up, and likely to stay up, and steel prices up, with no foreseeable letup in demand, automakers ought to run the math again.
The future is looking light.
(For the nostalgiac, here's Mr. McGuire delivering the hot tip.)