A Car Talk puzzler from last year asked which would save more fuel for the same number of miles driven - improving an old gas guzzler from 10 mpg to 11 mpg or trading in a hypothetical 100mpg car for a 200 mpg car. I did the algebra and it wasn't even close - the 10 to 11 mpg change saves way more fuel.

To put the example in more realistic terms, assuming 15,000 miles per year driven, trading in a 15 mpg car for a 40 mpg hybrid saves 625 gallons a year. Trading in the hybrid for a 80mpg plug-in hybrid saves 187.5 gallons a year for the same 15,000 miles.

The point isn't that we shouldn't try to develop 80 mpg or better cars but that right now we can save the most fuel by getting people out of gas-guzzlers. Fuel prices seem to be doing the trick.

Also, the article looks at what kind of technology could replace gasoline engines with nothing looking that promising. But something that is achievable now, with some R&D is the use of light weight metal alloys to build cars which could produce major gains in fuel efficiency. Although I don't know how much energy would need to be expended to develop such cars.

from 15 to 40, or even 35 exists right now and doesn't cost a fortune.

We could do even better if the EPA would relent on diesel emissions--while awaiting cleaner diesel engines.

The auto makers are well aware of the energy savings in weight reduction--that's why cars have so much plastic in them now.

What you have failed to grasp is that the "greens" are more focused on ideology than science. They want us off hydrocarbons, asap. Note the snide comment that non Prius hybrids don't sell as well because people cannot tell you're driving one. It is not enough to save fuel, you need public acclaim in doing it too!