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Are bigger cars safer?

(Page 2 of 2)

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.

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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 inĀ  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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