American roads looked different when the Insurance Institute for Highway Safety built its car-smashing crash test system in the early 1990s. Backup cameras didn’t exist, airbags weren’t mandatory, and safety rules had not yet killed the pop-up headlight. But perhaps the biggest difference is that cars were a lot less heavy—about a quarter lighter than the average vehicle today.

Raul Arbelaez, who oversees crash tests at the IIHS, has watched that transformation occur over his two-decade career, seeing sedans morph into “crossovers” and minivans become SUVs. The nonprofit lab tests most of the popular cars on the market and its safety endorsements are coveted by automakers. But until recently, he didn’t have a reason to question whether the IIHS equipment would be up to the task of crashing heavier vehicles. That reason was the Hummer EV.

At more than 9,000 pounds (4,000 kilograms), the electric SUV is about a third heavier than the weightiest vehicle IIHS has ever tested—which happens to be another EV, the Rivian R1T—and more than twice as heavy as the average American car, which weighs about 4,000 pounds. So Arbelaez bought a few cheap, old pickup trucks and began loading them up with concrete to match the Hummer’s weight. Despite the extra strain on the cables, the system held. The pickup went boom and a video of the test had a viral moment.

But Arbelaez is still worried. The trucks and SUVs that have taken over US roads in the past two decades protect their own passengers exceptionally well. But many of the same qualities that help a vehicle’s safety rating—including increased frame stiffness, size, and weight—also make them more of a menace to everyone else. Vehicle safety standards mostly reflect the safety of people inside a vehicle, not those outside. And despite improvements in safety technology and car design, heavier vehicles have contributed to increasing road deaths in recent years, according to data from the US National Highway Traffic Safety Administration—particularly among pedestrians, cyclists, and people driving smaller vehicles. Now EVs are tipping the scales even further. They often combine the beefy dimensions of supersize SUVs with a battery that itself weighs as much as a small sedan. Oh, and also blazing acceleration.

When WIRED put that to General Motors, spokesperson Mikhael Farah pointed to data linking pedestrian deaths to factors such as worsening pedestrian infrastructure and more speeding and drunk driving. (The same research noted that deaths due to SUVs were increasing faster than those due to cars, and that crashes involving heavier vehicles are generally more severe.) The company also pointed to safety features of the Hummer, such as upsized brakes and crash avoidance systems.

But Arbelaez is not alone in his concerns. Last month, in a speech to fellow safety experts, Jennifer Homendy, head of the US National Transportation Safety Board, made special mention of the “unintended consequences” of EVs—not just Hummers, but also electric Volvos, Fords, and Toyotas that carry thousands of pounds of extra weight beyond conventional cars of a similar size. “That has a significant impact on safety for all road users,” she said. 

It’s a tricky balance. Both Homendy and Arbelaez say they are excited about electric cars and care deeply about addressing climate change. But unless automakers or regulators find ways to reduce vehicle weights, they also fear a knock-on consequence of size inflation will continue unabated: that the only way to feel safe on roads with massive cars is to barricade yourself in one of your own. 

WIRED: So you’ve been crashing some really heavy vehicles. Why?