WASHINGTON — Electric vehicles, although subject to unique crashworthiness challenges, can generally lean on crash tests designed for vehicles with internal combustion engines.
Whether a vehicle is powered by a combustion engine, a battery or a combination of the two, the stored energy poses a potential safety hazard in a crash and, therefore, certain precautions must be taken by automakers and crash test engineers, vehicle safety experts told Automotive News in August.
“It’s building on the evolution of crashworthiness,” said Brian Latouf, global chief safety officer at Hyundai Motor Co. “It’s the same crash dummies. It’s the same injury protocols.”
NHTSA, for instance, conducts the same crash tests for electric and internal combustion engine vehicles to evaluate occupant protection as part of its consumer-facing New Car Assessment Program.
But EVs, Latouf noted, must also comply with Federal Motor Vehicle Safety Standard No. 305, which evolved from a separate standard aimed at reducing injuries and deaths from fires caused by gasoline leaks during and after vehicle crashes.
“One of the key requirements for 305 is energy storage, so your energy storage device during and after impact for the crash test has to be isolated,” Latouf said. “You can’t have exposed voltage to occupants, to first responders, so you have to isolate your battery pack from the vehicle and from its propulsion system.”
At Hyundai, that means running the gamut of crash tests required for gasoline-powered vehicles but, for EVs, also keeping the battery separate from other components in the vehicle to prevent shock hazard during and after a crash, as required by the standard.
Both NHTSA and the Insurance Institute for Highway Safety “actively measure and record that to ensure you have electrical isolation post-crash,” Latouf said. “They also observe the crashed vehicle for a period of time post-crash to see if a potential short could develop.”
NHTSA’s NCAP evaluates frontal, side barrier and side pole crash performance as well as rollover resistance. The agency also evaluates compliance with standard No. 305.
Jennifer Morrison, manager of vehicle safety, compliance, planning and development at Mazda North American Operations, likened the compliance test for standard No. 305 to a rotisserie chicken.
“They put the vehicle for NCAP on kind of like a large rotisserie spit, and they rotate it at 90-degree intervals for five minutes each to see if anything falls out of it,” she explained.
The purpose, she added, is to ensure there is no electrolyte spillage, that the batteries are retained within the vehicle and that there is no short between the battery and the chassis.
“So far, the crash tests that have been done of the all-electric vehicles are showing that they’re doing really well with the current set of tests. … Not having that heavy, mechanical engine up in front of our driver and passengers, there’s some benefits to that,” Morrison said. “You have an opportunity to rethink crash safety.”
NHTSA as soon as November is expected to issue a proposed rule-making that would add safety requirements for propulsion batteries in EVs and extend the applicability of standard No. 305 to heavy vehicles. The proposal also includes requirements to mitigate battery fires during normal vehicle operations — including exposure to water — while charging and after a crash.
For insurer-funded IIHS, there are some differences in how EVs are prepped and monitored during testing, but the ratings rely on the same fundamentals: structural intrusion, dummy injury measures and restraint performance.
The institute also closely monitors battery temperature during and after the crash. If the battery was compromised, it would be treated in a manner similar to a fuel leak in a gasoline-powered car: an automatic downgrade to a “poor” rating.
“The good news is, so far we’ve never observed any issues in our crash tests with thermal runaway or any shorts of any kind — anything that we would downgrade the vehicle for,” said Raul Arbelaez, vice president of IIHS’ Vehicle Research Center. “This isn’t surprising because by the time the vehicle gets to us, auto manufacturers have done a lot of work to make sure that vehicles perform well in our crash tests.”
The institute also assesses how much the structure around the occupant collapses in a crash. For EVs, that means looking at whether the battery compartment has been compromised.
“We don’t drop the battery compartment and open it up and make sure that nothing has been deformed,” he said. “We just make sure that the case hasn’t been cracked open and battery cells are shorted out or are falling out.”
Hyundai’s Latouf said a lot of work is done to structurally protect the energy system that stores all the voltage.
“We try to preserve that space during all the different crash tests. … If it’s a fully charged pack and it’s under incredible compression load, you could create a short, which could create a thermal event and also propagate into a fire, so you’ve got to be careful with that,” he said.
The institute, too, has looked at fire risk for EVs compared with internal combustion engine vehicles.
“So far, they’re actually not standing out in terms of elevated fire risk,” said Arbelaez, adding that any vehicle involved in “high severity crashes” — those that occur at speeds much higher than what are used in IIHS and NHTSA tests — could result in catastrophic fires and death.
“Even the best-performing vehicles that get very good ratings in the federal government’s crash tests and top scores in our frontal crash tests at 40 mph, when you crash them at 56 mph … their ratings effectively go from ‘good’ to ‘poor,’ ” he explained.
To be sure, there are millions of combustion engine vehicles on U.S. roads that have been studied over longer periods, and EVs are still ramping up in the U.S.
“We just need more data,” Arbelaez said, “and more time to be able to collect more data.”