Hybrids may be the great green hope, but new research shows that improvements to normal cars could reduce the nation's fuel consumption sooner and cheaper.

"We can absolutely reduce petroleum use and greenhouse gas emissions over the next 30 years," said Anup Bandivadekar of the International Council on Clean Transportation. "But in order to do that, we must halt increases in vehicle size and horsepower."

Bandivadekar and his former colleagues at MIT recently did a study on how to double the gas mileage (miles per gallon) of the average new car by 2035. They found that advanced technologies such as hybrids could help, but not by themselves and not anytime soon.