If John Kerry wins the presidency, most of us will be driving Chevettes — or the modern-day equivalent, at any rate. The Massachusetts senator has proposed jacking up federal fuel economy requirements for new cars to as much as 36 miles-per-gallon as part of his plan to reduce U.S. dependence on foreign oil. The problem is that only subcompact economy cars are capable of achieving nearly 40-mpg. If the government put such a requirement into place, if would in effect be outlawing mid-size and larger passenger cars — and all SUVs and pick-up trucks.

There is not a single 2004 model year pick-up or SUV that comes close to achieving 36-mpg. Mid-size family cars like the Honda Accord and Toyota Camry don’t make the cut, either — even in four-cylinder form. Equipped with V-6 engines, they’re not even in the ballpark.

Better get your V-8, before it’s too late…

Kerry has proposed these wrenching changes to reduce energy use and thus wean us away from our dependence on the oil produced by politically unstable Middle Eastern countries such Saudi Arabia, Iraq, and Iran. But the idea of imposing top-down fuel efficiency requirements is not a new one. It has been tried before — during the energy crisis of the 1970s.

It didn’t work then. And it won’t work now, either.

Federal Corporate Average Fuel Economy (CAFE) requirements have been in effect for decades — yet there has been no reduction in overall fuel consumption. Today’s cars and trucks are indeed more efficient than the cars of the 1970s and 1980s. But Americans drive greater distances as a result — burning more fuel each year than they did in pre-CAFE days. What makes Kerry think that people would drive less if their cars went even further on a gallon of gas? Or does he plan to impose restrictions on how many miles Americans may drive each year?

CAFE requirements have also had unintended side effects — most notably the boom in SUV and pick-up sales — which now account for about half of all new vehicles sold. When the original CAFE mandates came along, they effectively outlawed large, rear-wheel-drive passenger sedans and station wagons equipped with V-8 engines. In fact, just one such mass market model exists today — the Ford Crown Victoria. But the marketplace did an end run around CAFE by switching over to “light trucks” — SUVs and pick-ups. These formerly niche vehicles — mostly bought by farmers, contractors, and so on — were subject to a less-strict CAFE requirement. But these vehicles provided the same attributes people used to buy large sedans and station wagons for — roominess, size, and powerful engines. Thus the SUV boom was ignited — courtesy of CAFE and the law of unforeseen consequences.

Does Kerry have another “plan” to deal with the unforeseen consequences of CAFE II?

One consequence, though, is a sure bet. If the government imposes the draconian new fuel efficiency requirements Kerry is agitating for, the automakers will have to build smaller, lighter — and thus less safe — vehicles, just as they did in the 1970s. While non-engineers such as Kerry like to talk in generalities about “new technologies” that will somehow allow us to drive mid-sized and larger cars that also manage to return the fuel economy of subcompacts, the fact is such technology does not yet exist — and may never exist. The internal combustion engine has already been refined to the nth degree and significant improvements in fuel economy will be hard to come by — or very expensive. Few Americans — excepting perhaps a millionaire such as Kerry — could afford a $60,000 family car, even if it can get 40-mpg.

As before, the automakers will simply shave weight — and build smaller cars — to comply with CAFE II. And as before, people will die. It has been estimated that about 2,000 people are killed every year as a result of the CAFE-induced “downsizing” of the typical passenger cars — which lost about 1,000 lbs. on average between the 1970s and the 1990s. All the air bags and crumple zones in the world won’t prevent a similar body count in the event Kerry’s proposal becomes law.

But only if Kerry becomes president first.