MarketWatch is reporting that lighter, better-designed cars of the future could cut down on harmful greenhouse emissions and raise gasoline mileage without compromising safety. That's according to a new report released Thursday from the Rocky Mountain Institute. This runs against the conventional wisdom about how heavy cars usually fare better in accidents than lighter cars.

"When they think about crashworthiness, both consumers and those with more extensive involvement in automotive safety often revert to thinking in terms of the laws of physics -- if a heavier object hits a lighter one, the lighter one will rebound further/faster or suffer more damage," Laura Schewel, author of a Rocky Mountain Institute study entitled "Triple Safety," wrote in the report. It was released at the recent Society of Automotive Engineers World Conference in Detroit.

She advocates using more aluminum and composite materials in vehicle construction. "Cars are not simple, solid objects; they have crush zones and structural features designed to absorb impacts. In other words, length and design are more important than weight," the report said. "While a light car does tend to experience a faster deceleration than a heavy car in a two-car crash, this is only one of several factors in determining occupant safety."

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