During a keynote speech to the Transportation Research Board annual meeting Wednesday, National Transportation Safety Board (NTSB) Chair Jennifer Homendy questioned the safety impact of electric vehicles.

I’m concerned about the increased risk of severe injury and death for all road users from heavier curb weights and increasing size, power, and performance of vehicles on our roads, including electric vehicles.

A GMC Hummer EV weighs over 9,000 pounds, up from about 6,000 pounds. Its gross vehicle weight rating is a staggering 10,550 pounds. The battery pack alone weighs over 2,900 pounds—about the weight of a Honda Civic. The Ford F-150 Lightning is between 2,000 and 3,000 pounds heavier than the non-electric version. The Mustang Mach-E, Volvo XC40 EV, and RAV4 EV are all roughly 33% heavier. That has a significant impact on safety for all road users.

Now I want to be clear: I am inspired by the Administration’s commitment to phasing out carbon emissions. We do have a climate crisis that needs to be addressed. The US transportation sector accounts for the largest portion of US greenhouse gas emissions, and I firmly believe it is a human right to breathe clean air. But we have to be careful that we aren’t also creating unintended consequences: more death on our roads. Safety, especially when it comes to new transportation policies and new technologies, cannot be overlooked. Ever.

—Jennifer Homendy

In a Comment piece published in Nature in 2021, researchers from the University of Calgary, UC Berkeley, and Carnegie Mellon University made a rough calculation comparing mortality costs and climate benefits that found that the cost of extra lives lost from a 700-kg increase in the weight of an electrified truck rivaled the climate benefits of avoided greenhouse-gas emissions.

Electrifying vehicles adds yet more weight. Combustible, energy-dense petroleum is replaced by bulky batteries. And the rest of the vehicle must get heavier to provide the necessary structural support. The electric F-150 weighs 700 kg more than its petrol-powered predecessor. Smaller electric cars are heavier than their petrol equivalents, too.

Why does this matter? First and foremost is safety. The likelihood of passengers being killed in a collision with another vehicle increases by 12% for every 500-kg difference between vehicles. This added risk wouldn’t apply if everyone drove cars of similar heft. But until they do, the number of casualties in crashes is likely to increase as heavy electric vehicles join lighter existing fleets. Pedestrians will also be at risk. If US residents who switched to SUVs over the past 20 years had stuck with smaller cars, more than 1,000 pedestrian deaths might have been averted, according to one study.

Heavier vehicles also generate more particulate pollution from tyre wear. They require more materials and energy to build and propel them, adding to emissions and energy use.

—Shaffer et al.

Shaffer et al.

The researchers suggested that taxing heavy cars could be part of a solution, along with driving less, and other technology-based weight reductions efforts.

Ultimately, to manage climate change, the world needs to stop emitting greenhouse gases from vehicles and power plants. Electric vehicles powered from a clean grid are an essential step in the right direction. A focus on driving lighter, safer, cleaner and less can ensure a better future for everyone.

—Shaffer et al.

Resources

• Blake Shaffer, Maximilian Auffhammer & Constantine Samaras (2021) “Make electric vehicles lighter to maximize climate and safety benefits” Nature 598, 254-256 doi: 10.1038/d41586-021-02760-8