Are you 15 percent more likely to die in a car that’s 300 pounds lighter?

Talk-radio host Lars Larson went after President Barack Obama in a news post recently, claiming that the White House’s attempts to increase vehicle fuel mileage will end up killing some of us. The post is tantalizingly called, "Obama is going to kill some of you."

How will that happen? Well, Larson says, the auto industry will do whatever it takes to stay in business, including making cars "very, very small." This is how Larson explains it:
 

"They’re going to peel hundreds and hundreds of pounds of weight off the cars that you drive to achieve the government ordered corporate average fuel economy, even though America is sitting on an ocean of available oil.

Every time the weight of that vehicle is reduced by a hundred pounds, your chances of dying are going to go up by about 5 percent. Peel three hundred pounds off – you’re 15 percent more likely to die in that car."

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We need to back up here. The Corporate Average Fuel Economy, or CAFE, regulations are intended to improve the fuel economy of vehicles so we don’t guzzle so much oil. Obama  announced last year a goal of an average 54.5 miles per gallon by 2025. The fleet average today is about 27 miles per gallon.

Conservatives tend to argue that automakers will respond by making cars lighter and, therefore, more dangerous. But it’s important to note that the regulations set different goals for vehicles based on type. In other words, large sports utility vehicles don’t have to meet the same mileage goal as compact cars.

That’s the backdrop. We turned to Larson.

He cited a 2003 study by the National Highway Traffic Safety Administration, which found that a 100-pound reduction in smaller cars resulted in a 4.39 percent increase in fatalities. The study looked at fatality data from 1995 to 2000, involving 1991 to 1999 model vehicles. Let us emphasize, the statistic applied only to vehicles weighing less than 2,950 pounds -- not all vehicles. For larger vehicles, the increase was about 2 percent. (What’s a car in the higher-risk category? A 1995 Honda Accord LX is about 2,900 lbs.)

So the statistic exists, but we wondered: Surely vehicles have come a long way since 1999?

We turned to a spokesman for the U.S. Department of Transportation, who forwarded us an updated version of the 2003 study with new numbers.

And guess what? The 2011 study shows that for lighter cars weighing less than 3,106 lbs, the chances of dying go up 1.44 percent for every 100-pound reduction, if you maintain the same vehicle size or "footprint" as they call it.

That’s a much smaller difference.

Tom Wenzel is a research scientist at Lawrence Berkeley National Laboratory who also studies vehicle size, weight and fatality statistics. He explained the differences in the two studies.

One, he said, the 2003 study assumed weight reduction would be accompanied by size reduction, but that’s not necessarily the case. Two, he said, vehicles have quite simply changed in the last decade, to become safer without the added weight. The later study looked at vehicles made between 2000 and 2007.

The 4.39 percent figure is one statistic at one point in time, Wenzel said. Tweak the factors that go into the model to get that figure and the numbers change.

NHTSA acknowledges the variety of opinions. At a one-day workshop on the topic of mass, size and safety the agency’s deputy administrator said that researchers have come to different conclusions: "Some associated a significant fatality increase with mass reductions, while others associated a fatality decrease with mass reduction."

Finally, we checked with the Insurance Institute for Highway Safety. Spokesman Russ Rader generally agrees that larger is safer. "All cars are much safer than they used to be, but the laws of physics haven’t been repealed," he said. "So the differences are still there: that is, people riding in small, lightweight cars get less protection in crashes than people in bigger, heavier ones."

He pointed to a 2010 analysis of driver death rates per million showing that mini-cars, like the Honda Fit, had a death rate of 70 per million registered vehicles of that size. That’s double the rate for very large cars, 32 per million. And, sure, that makes sense.

But, we’d be remiss if we didn’t point out in the same chart that midsize cars, like the Honda Accord, had a death rate of 37 per million -- which is close to the largest cars. (Rader’s response? Midsize cars do a good job, too.)

We wanted to give a variety of sources and opinions, but we have a ruling to make.

Larson cited a study figure that was largely accurate in 2003, but only as applied to vehicles under a certain weight. And those numbers have been updated by the original researcher to reflect a much smaller increase that is significantly different from Larson’s statement.

Larson argues that his statement is accurate. His point remains that increasing fuel mileage -- from the mid-20s to 55 miles per gallon by 2025 -- will have to come from reducing weight and technical advancements, but he thinks it’s more of the former rather than the latter.  

"Reducing weight degrades safety. I told the listener that it makes death or injury more likely," he wrote in an email.

Researchers and others in the industry are somewhat divided on how much weight to give weight in calculating safety, but they acknowledge that Obama is not demanding that all of us start driving Honda Fits.

We apologize for picking on Hondas. We don’t apologize for our ruling. We rate the statement Mostly False. It contains a nugget of truth -- it came from a 2003 report -- but the number is out of date and narrow to boot.