The United States consumes 390 million gallons of gasoline a day. Even if you believe climate change is the greatest hoax since Orson Wells convinced the country it was under Martian attack, we can't sustain that kind of consumption because the supply of oil is dwindling and what remains can't be pumped much faster.

By embracing small, lightweight cars with hyper-efficient engines, alternative fuels and hybrids we can cut our fuel consumption 30 to 50 percent by 2035, say researchers at the Massachusetts Institute of Technology. Improvements in vehicle design and engine efficiency, hybrid technology and the inevitable electrification of automobiles will go a long way toward slaking our thirst for gas, they say, but the biggest benefit will come when people realize they don't need the fastest car or biggest truck on the block to slog through our daily commutes or run to the store for a quart of milk.

"We've got to get out of the habit of thinking we only need to focus on improving the technology, that we can invent our way out of this situation," says John Heywood, the mechanical engineering professor who led the study. "We've got to do everything we can think of, including reducing the size of the task by real conservation."

The idea that smaller cars and hybrids are more fuel efficient isn't new, but On the Road in 2035: Reducing Transportation's Petroleum Consumption and GHG Emissions (.pdf) lays out a comprehensive approach to reducing our fuel consumption to 2000 levels and significantly curbing greenhouse gas emissions.

Over the next 15 years or so, automakers must increase the efficiency of gasoline and diesel engines and transmissions and significantly reduce the weight of the cars they build. These improvements should be focused exclusively on improving fuel economy, not improving performance, the researchers say.

Looking 15 to 30 years ahead, the researchers say automakers must continue developing hybrids, plug-in hybrids, electric vehicles and hydrogen fuel cell vehicles.

Develop alternative fuels, but don't expect them to supplant petroleum anytime soon. Relying on corn-based ethanol "is not obviously justifiable," they write, but biodiesel, algal fuels and cellulosic ethanol should be pursued.

The government needs to get involved "to push and pull improved technologies and greener alternative fuels into the market place in high volume." Policymakers should "require auto manufacturers to make smaller, more fuel efficient cars, encourage consumers to chose those vehicles and discourage everyone from driving so much."

Heywood and his colleagues started working on the study five years ago, when gas was well under two bucks a gallon and SUVs ruled the earth. Since then, we've seen prices approach $5 a gallon in some areas and the bottom fall out of the auto industry as consumers ditch their gas-guzzlers faster than Christie Brinkley dumped Peter Cook.

The auto industry has gotten the message and is pursuing many of the points the researchers make. They're all working on smaller, more fuel-efficient gasoline engines, dual-clutch transmissions and clean diesels while paring weight from their cars. Internal combustion isn't going anywhere anytime soon, and the researchers say it "offers a path for continuous improvements in vehicle efficiency for the next few decades" – provided automakers emphasize fuel economy over performance.

Most of the automakers also are developing hybrids, which the researchers say "offer a promising path to cost-effective reduction in fuel use," and plug-in hybrids. But the timeline for their impact on fuel consumption will be measured in decades because of their slow rate of market penetration. Toyota's sold 1 million Prius hybrids in the 10 years it's been on the road, and hybrids are still less than 3 percent of the market. That number will surely climb, but "their impact on fuel use and emissions is unlikely to be significant over the next few decades." The time line, they say, is longer still for electric and hydrogen vehicles because of their cost and other issues.

Critics argue the auto industry is dragging its heels and we need these cars tomorrow. But if super-efficient vehicles appeared in every showroom tomorrow, it still would take two decades or more for them to have a significant impact. Cars have a lifespan of about 15 years, and "fleet fuel use responds with a lag time of some 10 years to changes in the new vehicle market," the researchers say.

"Transitioning from our current situation onto a path with declining fuel consumption and emissions, even in the developed world, will take several decades – much longer than we hoped and realized," Heywood says. "We've got to start now."

Photo by Flickr user Mr. Wright.