It was one of several common tropes used 10 years ago against proposed regulations to boost average fuel economy.

"More efficient cars will have to be lighter-weight, and they'll be unsafe because in accidents, they'll crumple up like Kleenex."

Logical conclusion: if you require higher fuel economy in cars, more people will die in crashes.

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Now a new study purports to show that's not true, using data to prove it. Unfortunately, the analysis is flawed.

It was never going to be true, frankly: crash safety is now so important to buyers that substandard ratings can severely affect a car's sales potential.

All automakers go to great efforts to get top marks on crash-safety tests conducted by the NHTSA and the IIHS.

Erwin Wurm's Fat Car

Erwin Wurm's Fat Car

And corporate average fuel economy has risen steadily since 2012, in line with regulations that require it to do so, and at lower cost than projected when the rules were finalized.

Makers have used a combination of smaller engines, more advanced transmissions, better aerodynamics, and lower weight to boost efficiency incrementally.

So-called "lightweighting" has taken 100 to 300 pounds out of newer generations of vehicles, even as they add interior volume and many new features to keep pace with competitors.

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Those lighter weights have spread throughout new cars over the last decade.

A notable early example was the Mazda 2 subcompact, now discontinued for the U.S. market, which was fully 100 pounds lighter than its predecessor when launched in 2008—a remarkable achievement at the time.

On Wednesday, The Washington Post covered a recent new study by the National Bureau of Economic Research (which you'll have to purchase to read in full).

54.5 MPG CAFE standard for 2025

54.5 MPG CAFE standard for 2025

The study's precis, however, sums it up quite neatly:

Using unconditional quantile regression, we are the first to document the effect of the Corporate Average Fuel Economy (CAFE) standards on the vehicle weight distribution.

We find that on net CAFE reduced fatalities, with lowered mean weight dominating increased dispersion.

When monetized, this effect suggests positive net benefits from CAFE even with no undervaluation of fuel economy.

Read that again: lighter cars reduce crash fatalities. (Analysts have moved away from use of the word "accident," which suggests that no party is really to blame for a crash.)

The researchers who published the NBER analysis collected weight data for vehicles sold in the U.S. from 1954 to 2005, and analyzed reports of 17 million crashes from 1989 through 2005.

2015 Ford F-150 aluminum body shell

2015 Ford F-150 aluminum body shell

For each one, they noted the weights of the vehicles involved and whether the crash caused one or more fatalities.

Vehicle weight started to decline after the original set of CAFE standards were introduced in 1975 and a first round of lighter vehicles began to hit the roads over the next 10 years.

The original argument that lighter-weight vehicles may increase injuries or deaths from crashes between vehicles works if you lighten one vehicle while keeping the other at a constant weight.

But that's not what's happening as CAFE standards continued to make new vehicles more fuel-efficient: every new vehicle got lighter.

That means that the entire pool of cars on the road is slowly getting lighter—at the same time, we'd point out, that crash-safety tests have gotten more stringent.

GM’s front center airbag in action

GM’s front center airbag in action

The paper, however, appears to lack any discussion—or even recognition—of the fact that safety standards notably strengthened for all new cars sold between 1989 and 2005, the period of the crashes studied.

The sole relevant sentence we found in the report said, "Firms may respond [to driver nervousness about lighter cars] by putting safety devices into at-risk vehicles to reassure drivers."

But in fact that's exactly what happened to all cars: in 1989, only a few cars had even a single airbag, for instance, while by 2005, six airbags was the standard.

Without addressing the mandated improvement in crash safety and survival equipment in cars during the period studied, the conclusion that lighter cars actually improve safety seems unwarranted.


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