American Debra Miceli with her Monstertruck Madusa during the United States Hot Rod Association Monster Jam in Switzerland.

Are bigger cars safer?

Mention federal fuel efficiency standards – particularly Obama's new standards – to hardline capitalist types, and watch as they suddenly morph into Ralph Nader.

"Proposed mileage standards would kill more Americans than Iraq War" writes Steve Milloy, a Fox News commentator and author of "Green Hell: How Environmentalists Plan to Ruin Your Life and What You Can Do to Stop Them."

"[The Obama adminstraton's proposed efficiency standards] will raise the prices of cars, and make them less safe," writes Megan McArdle, a libertarian blogger for the Atlantic.

[Corporate Average Fuel Efficiency] is among the deadliest government regulations we have," says Sam Kazman, the general counsel for the Competitive Enterprise Institute, a free-market think tank (which, incidentally, has taken in more than $2 million in funding from ExxonMobil).

Mandating fuel efficiency, the argument goes, will force automakers to design smaller, lighter vehicles, which are more dangerous to drive than bigger, heavier ones.

Are bigger autos really better at protecting their occupants? All else being equal, yes. Last month, the Insurance Institute for Highway Safety (IIHS), a nonprofit funded by auto insurers, released a report [PDF] that found that both the size and weight of a car are crucial to protecting people in crashes.

To test this, the IIHS crashed a Honda Fit into a Honda Accord, a Smart Fortwo into a Mercedes C class, and a Toyota Yaris into a Toyota Camry, all head-on at 40 miles per hour. In each case, the dummies in the bigger car were more likely to walk away from the collision (or, at least, they would have been if they weren't dummies).

It boils down to Newtonian mechanics: When two objects of differing masses collide, the less massive object will undergo a greater change in velocity, which means a higher risk of injury for the poor schlubs inside that object.

Size also matters, particularly the length of the car's front end. The bigger it is, the slower the sudden stop is in a crash.

"The whole idea of crashworthiness design is to help slow occupants down over time in a crash, and you have less opportunity to do that in a small car," says Russ Rader, a spokesman for the IIHS, in a phone interview.

At this point, you would be equally justified in saying that it's really the bigger cars that are unsafe because they are more likely to wreck the smaller ones. This is certainly true for when two vehicles collide, but the IIHS report also points out that smaller cars are also less safe when crashing into stationary objects. As the report notes, almost half of all crash fatalities in minicars occur in  so-called single-vehicle crashes.

But to conclude that bigger is better is to oversimplify. Cars are not billiard balls, and there are lots of other things other than mass that determine how they will behave in a collision. That's why, as Big Money blogger Matthew DeBord points out, the Mini Cooper gets a better safety rating than the Chevy Trailblazer, which is more than twice as heavy.

"Good engineering and good design are better protective measures than mass," says auto expert Michael Brylawski, a senior adjunct fellow at the Rocky Mountain Institute and a vice president at Bright Automotive, in a phone interview.

Mr. Brylawski's design philosophy advocates "decoupling size from mass," that is, designing cars that have big, energy-absorbing crumple zones but are also made of lightweight materials, such as aluminum or carbon fiber, so that they require less fuel (and are less likely to hurt those outside the vehicle).

What's more, as Brylawski pointed out, there are many ways to increase fuel-efficiency that have nothing to do with making the car lighter. You can improve the aerodynamics, the tires, and even the air conditioning. And, of course, you can make the powertrain more fuel-efficient, or even make it electric.

"Don't underestimate American automotive engineers to be up to the challenge," said Brylawski.

Past federal fuel standards mandated an average fuel efficiency for a manufacturer's entire fleet. This set up an incentive for automakers to make a lot of small, light cars to offset the big, heavy models. In an attempt to remove that incentive, Obama's plan does away with fleet average requirements and replaces them with different standards for vehicles of different sizes.

"People are still going to be driving their SUVs," Brylawski says. "But they're going to be lighter."

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