When electric vehicles were first tested, the automotive community was primarily concerned with fire risk, as everyone quickly realised that lithium batteries, when damaged, can ignite. As a result, the industry has special procedures for EV testing, such as battery monitoring and having firefighters on hand, the policies have had a significant impact, and the question of safety is now concerning the extra weight of electric vehicles.
Raul Arbelaez, Vice President of the Vehicle Research Center, IIHS, says his biggest concern has shifted and now asks "what all that extra vehicle weight means for the safety of people on the road, specifically occupants of lighter vehicles as well as pedestrians and bicyclists".
Electric vehicle sales are taking off, and soon, electric vehicle sales will eclipse the sales of internal combustion vehicles. As more models go to market, more cars will be tested, and there are already massive differences in vehicle weight since the first electric vehicle was tested at IIHS in 2011.
"We expect to test a lot more electric vehicles in the coming years. As a result, many electric cars, SUVs and pickups will be contenders for our TOP SAFETY PICK and TOP SAFETY PICK+ awards. As with most vehicles on the U.S. market, we will put them through their paces. However, there's a big difference between the first all-electric vehicle we tested - a 3,339-pound 2011 Nissan Leaf - and the current generation of EVs, many exceeding 6,000 pounds. These large SUVs and pickups are packed with power that requires a massive battery,". Says Raul Arbelaez. "To put this extra weight in context, when I first heard about the 9,500-pound GMC Hummer EV, I had a practical concern. Would our crash test machine at the VRC be able to manage it? Could we pull a vehicle like this up to our test speed of 40 mph without breaking our machine? To find out, we got some old junkers, loaded them with steel plates and a concrete block to get the weight up to about 9,500 pounds. Then we sent them down the runways. Everything worked; all we needed was a little extra charging time for the hydraulic system and a bit more clamping force on our tow cable to keep the vehicle in place".
Less easily solved is the problem the extra weight poses when a hefty electric vehicle crashes into a much lighter nonelectric car or SUV with a typical weight of 3,000-4,000 pounds.
"When two vehicles collide, the heavier vehicle pushes the lighter one backwards, resulting in higher forces on the people in the more lightweight vehicle and lower forces on people in the heavier vehicle. That's why we stipulate that our frontal crash test ratings - which are conducted against a fixed barrier and simulate a crash with an identically sized vehicle - can only be compared among vehicles of similar weight".
IIHS has conducted several demonstration crashes that paired larger vehicles with smaller ones to show the effect of size and weight on impacts. In two 2018 tests, one involving a midsize SUV and a small car and another involving a large car and a minicar, both the smaller vehicles performed poorly, despite good ratings in IIHS tests.
"Assuming the new generation of heavy EVs is designed to perform well in crash tests, there is no reason they can't provide good protection to their occupants. In fact, their extra weight will afford them greater protection in a multivehicle crash. But, unfortunately, given the way these vehicles are currently designed, this increased protection comes at the expense of people in other vehicles,". says Arbelaez.
He continues "The extra weight of electric vehicles can also present a threat to pedestrians and bicyclists, though the danger for them is more complex. The weight differential between a person and any passenger vehicle is already so enormous that the additional weight from an EV battery would make little difference in most cases. (Large vehicles represent a more significant threat to pedestrians and bicyclists, primarily due to their height and shape, which affect both visibility and whether a person is knocked to the ground when struck). However, it needs to be clarified that all EVs have braking performance that matches their additional mass. If the extra weight leads to longer stopping distances, that will likely lead to an increase in pedestrian and cyclist deaths, which already have been on the rise in recent years".
While there are questions about braking performance, electric vehicles have no problem accelerating. Unfortunately for crash & safety, today's supersized EVs are a double whammy of weight and horsepower. While there were many heavy vehicles on our roads before the e-mobility revolution, a delivery truck was not designed to go from 0 to 60 in around three seconds like the Hummer or the 7,000-pound Rivian R1T pickup. Even the more modest Kia EV6, a small SUV that weighs about 4,500 pounds, boasts the same rapid acceleration," says Arbelaez.
Suppose the present trend toward ever-heavier, more powerful EVs continues. In that case, there will be a big increase in the number of super-heavy, high-acceleration machines around us, including in residential neighbourhoods. That will make a collision involving a huge weight disparity much more likely.
Arbelaez is not suggesting putting the brakes on electrification. There are good reasons for it, but he stresses its development will require new thinking about the kinds of vehicles people want on their roads.
"For one thing, as a society, we should consider how much mass individuals should be driving around for the daily commute and around town. There are EVs with more moderate weights. (Remember that Leaf?) The heaviest of the new EVs are heavier because they are bigger, but also because larger batteries afford them more extended range and higher horsepower".
Arbelaez continues, "The ability to travel 400 miles on a charge is convenient but unnecessary for most commutes. As charging speed and infrastructure improves, it will arguably be less important for road trips too. As for horsepower, is the kind of rapid acceleration the new models boast really important or even a good idea? Vehicles with extreme levels of power simply encourage more speeding, which leads to more fatal crashes".
If substantially reducing EVs' weight is not an option, automakers should consider other design changes to improve crash compatibility. For example, heavier vehicles could be built with additional crush space in their front ends to help compensate for the effect of their extra weight in a crash with another vehicle.
While engineers usually consider crumple zones important for protecting a vehicle's occupants, additional space would also protect people in other, lighter cars. In addition, with no engine taking up space in the front of the vehicle, there may also be more flexibility in designing front ends that are less likely to injure pedestrians and bicyclists.
Arbelaez concludes with advice how the automotive community should progress, "I'm hopeful that expected improvements in battery technology will help by allowing smaller batteries to store more energy and that an expanding network of fast public chargers will take away some of the need for long ranges.
In the meantime, we need to double down on existing solutions. Manufacturers should equip all new vehicles with high-performing crash avoidance systems that recognise and brake for pedestrians and bicyclists, in addition to other vehicles, and good headlights that allow drivers to react quickly at night. In addition, states and local governments should consider lowering speed limits, factoring in the increased danger from weight disparities, and backing them up with increased enforcement. Electric vehicles are here to stay, but we can choose what that means for safety".
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