Smaller, lighter cars always get the blame when politicians want to lower fuel-economy standards.

They lobby that too many Americans will be driving lighter cars and that that will lead to more deaths on America's roadways.

That's exactly the argument that the Trump administration made earlier this month in its proposal to weaken fuel economy standards and freeze them at 2020 levels through 2026.

Questionable safety benefits

Its proposal, dubbed the "Safer Affordable Fuel-Efficient Vehicles Rule" (SAFER), claims that lowering the fuel-economy standards will reduce highway fatalities by about 1,000 per year, or 12,700 over the lifetimes of all cars produced through 2029. 

It argues that reducing weight is one of the cheapest strategies automakers can use to improve their cars' fuel economy, and that these lighter cars won't be as safe as heavier cars would be.

EPA Acting Administrator Andrew Wheeler

EPA Acting Administrator Andrew Wheeler

The finding mirrors a study NHTSA conducted in 2003, which found that for every 100 pounds a car dropped in weight, it increased the odds of dying in a crash by almost 5 percent. (The study is no longer available in NHTSA's public archives online.) 

That report was later debunked by an Energy Department report that showed it only applied to cars lighter than 2,950 pounds. Raising that cutoff to 3,106 pounds, the later report noted, reduced the effect of a 100-pound weight reduction to a 1.5 percent increase in risk of a fatal accident.

The 2011 report, titled "Assessment of NHTSA’s Report ‘Relationships Between Fatality Risk, Mass, and Footprint in Model Year 2000-2007 Passenger Cars and LTVs" [PDF] also noted that effect only applied if cars did not simultaneously increase in size. 

Bigger cars

Yet that is exactly what cars have done since today's fuel-economy standards were implemented in 2012.

The 2012 fuel economy standards that the government is proposing to replace sets lower fuel economy standards for larger cars, based on their "footprint," the area bounded inside the cars' wheels. That has given automakers an incentive to bump up the size of vehicles across the board to minimize the standards they have to meet.

A study last year by looked at seven of the most popular cars on the market of various types—the BMW 3-series, Chevy Corvette, Dodge Grand Caravan, Ford Explorer, Honda Civic, Toyota Camry, and VW Jetta—and showed that they all grew 1 to 4 inches longer after redesigns that followed 2012.

Making vehicles larger improves safety independent of weight, because larger vehicles offer more crumple space to absorb the impact forces of an accident before encroaching on passenger space.

On Page 281 of the SAFER proposal to freeze fuel-economy standards, it notes that the government's analysis is "best suited to predict the effect of a small change in mass, leaving all other factors, including footprint, the same. With each additional change from the current environment (e.g., the scale of mass change, presence and prevalence of safety features, demographic characteristics), the model may become less accurate."

Better safety technology

It also barely mentions improved safety technology, such as more air bags, stronger roofs, standard electronic stability control, and active lane control in its safety estimates.

All these features and more have become standard or commonplace on cars since 2008. 

A 2015 study by IIHS showed the effects of vehicle technology improvements on safety through 2011. It showed that factors such as universal electronic stability control, better crash structures, and increased use of air bags reduced death rates by about a third between 1998 and 2010.

More recently, IIHS said it expects that new technologies such as automatic emergency braking and active lane control can prevent another 8,000 highway deaths per year.

2009 Chevrolet Malibu vs 1959 Chevrolet Bel Air

2009 Chevrolet Malibu vs 1959 Chevrolet Bel Air

When the IIHS crash tested a 1959 Chevrolet Bel Air into a 2009 Chevy Malibu to show how much safety improved in 50 years, the smaller Malibu was also about 180 pounds lighter than the Bel Air and fared much better in the crash.

All this begs the question whether lighter cars are still less safe in an era when most cars are getting bigger and safety technology is advancing rapidly.

The SAFER proposal barely addresses these questions, and minimizes the safety improvements that have already been made as cars have become more fuel efficient under the existing standards.