Size or Speed? IIHS Study Examines Safety Between Models

With the rate of fatal automotive accidents having spiked dramatically in recent years, just about everyone has been theorizing why. While there still seems to be a level of willful ignorance surrounding how modern infotainment systems and driving aids create more opportunities to be distracted behind the wheel, most outlets tracking safety seem to have come to the realization that size disparities between vehicles play an important factor in crash survivability.

The Insurance Institute for Highway Safety (IIHS) recently published a list of the models with the highest death rate per million vehicles registered. Its takeaway seems to be that the uptick in fatalities could be attributed to smaller vehicles and powerful models that encourage aggressive driving.

“Overall, newer vehicles are much safer than those of the past,” said Chuck Farmer, IIHS vice president of research and statistical services, who calculated the death rates. “But, unfortunately, there are still major differences in the levels of protection that various models provide. There was also a spike in speeding-related fatalities during the pandemic, which may help explain why we find so many muscle cars among the worst performers for this period.”

The vehicle that saw the most per capita deaths (2018-2021) was the Mitsubishi Mirage G4. The model had an unfortunate, commanding lead and was followed by the hatchback variant.

However, vehicle mass likely wasn’t the singular factor here. Because the little Mitsubishi was pursued by the Dodge Challenger. From there, it’s another batch of microscopic cars before we get into a mix of domestic performance vehicles, small commuters, and the occasional midsize sedan.

From the IIHS:

The average driver death rate for all 2020 and equivalent models increased to 38 deaths per million registered vehicle years, compared with 36 for 2017 models. That’s a further increase from a low of 28 for 2011 models following a steady decline since the 1970s. The rise is consistent with a larger number of U.S. traffic fatalities over the four-year period covered by this study, compared with the previous one. From 2018 to 2021 there were 155,136 fatalities, compared with 147,599 from 2015 to 2018.

Minicars had the highest driver death rates, averaging 153 deaths per million registered vehicle years. Very large luxury cars had the lowest, averaging only 4 deaths. In contrast, very large pickups had the highest other-driver death rates, averaging 121 deaths, while small sports cars had the fewest other-driver deaths, averaging only 11 per million registered vehicle years.

The average other-driver death rate for all 2020 and equivalent models was 53 deaths per million registered vehicle years. There are more other-driver fatalities than driver fatalities because these newer models are more crashworthy than many of their crash counterparts, which come from the wider U.S. fleet, made up of mostly older vehicles.

But, if size and speed are really the biggest factors, one might wonder why the Mazda MX-5 and Mini Cooper aren’t on the list. The Mirage may be the smallest vehicle presently available on our market but it’s only a couple inches shorter than they are and boasts none of their fun-loving attitude.

The IIHS faulted Dodge, Ford, and Chevrolet for marketing their vehicles in a manner that encourages aggressive driving. But they’re not the only performance models that exist on our market and don’t appear to have contributed to fatalities pertaining to other drivers at anywhere near the frequency of large pickups and SUVs. While we could assume domestic muscle simply has a tendency to slap into more guardrails than people, there could be another explanation. Overall size and powertrain zestiness may not be the only contributing factors to how much carnage a vehicle can create. The overall shape of an automobile remains relevant.

We already know that tall vehicles with a flat face result in lower survivability rates for struck pedestrians. Cars boasting a lower hood are more likely to see their victim rolling over the top, while the shape of larger pickups and SUVs has a tendency to pull a body beneath the wheels after the initial strike.

But that same phenomenon may also apply when automobiles crash into each other. Many of the vehicles that performed poorly in terms of per capita fatalities were comparatively lightweight with lower belt lines. It may also be worth noting that convertible sports cars tended to perform worse than their hardtop brethren. This sizing/shape disparity is a speculative theory. But one that’s supported by the laws of nature and something yours truly has long believed contributes to increases in fatal accidents. I would argue this dramatically impacts safety overall and helps explain why the IIHS noted that pickups had the highest instance of “other-driver death rates” and sporting vehicles boasted the lowest.

The concept was drilled into your author’s head as a youth while attending motorcycle safety courses. One of the first things they teach you is how much more vulnerable you are than a motorist surrounded by a steel cage. But the concept carries over to individuals driving smaller automobiles, as physics won’t be on their side should they go head-to-head with a much larger vehicle that’s tall enough for the grille to ride up during a wreck.

But there are outliers in the IIHS data. While the vehicles appearing to boast the highest levels of occupant safety tended to be pickups and larger SUVs, names like Subaru Outback, Lexus ES 350, and even Toyota C-HR also made the list.

Meanwhile, vehicles boasting the highest rate of “other-driver deaths” were all large pickups. But the rest of the field was varied and included a staggering amount of Stellantis products. There were also a few vehicles that carried over from the driver-death list — including the Kia Rio, Kia Optima, Kia Forte, Dodge Charger, and Nissan Altima.

This might indicate that there are a few models boasting lower-than-average safety or perhaps cater to a clientele that’s not terribly interested in safe driving.

The IIHS also speculated that crash avoidance systems and other advanced driving aids played a factor by noting they were standard equipment on most luxury vehicles that tended to perform better overall. It’s certainly a possibility. But the outlet seems to have a vested interest in shaping the insurance landscape and has long championed these systems without much criticism. We’d argue there’s a broad disparity in how they function between models and suggest that certain systems may actually do more harm than good while others (e.g. blind spot monitoring) seem to be a net positive.

Data also didn’t support that power and speed were enough to do a model in all by itself. The IIHS noted that the Audi A4 and Mercedes-Benz E-Class offered nearly as much horsepower as some of the worst performers on the list. But it claimed that the image of premium luxury vehicles differed from the American muscle cars and that it could make all the difference.

“The explanation may lie in the image of the vehicles. Luxury cars are associated with ease and comfort,” reads the report. “In contrast, the muscle cars on this list are associated with the early days of the drag strip, as illustrated by features like racing stripes, hood scoops and spoilers, and that seems to influence how they’re driven.”

“Marketing for the Dodge Charger HEMI, for example, focuses on its ‘ground-shaking’ power, its acceleration ‘bolting off the line’ and its ‘racing-inspired” high-performance brakes, while the Chevrolet Camaro promises buyers the ability to “dominate on the daily’ with an ‘extreme track performance package’ and the Ford Mustang offers ‘adrenaline chasers’ the power to ‘keep ahead of the pack.’”

“These two lists illustrate some of the intangibles of crash risk,” said IIHS President David Harkey. “We can measure horsepower and weight and test for crashworthiness. However, the deadly record of these muscle cars suggests that their history and marketing may be encouraging more aggressive driving.”

It’s plausible. But the premise feels over-hyped when the vehicles in question are mixed in with a slew of economy cars boasting the same level of risk to the occupants. Most muscle cars also failed to represent an elevated risk to other drivers vs large pickups and SUVs. That seems important, especially if the drivers' oversized vehicles represent a larger risk to their fellow motorists.

But you'll have to make up your own mind on the biggest contributing factors and are welcome to browse the full study to that end. While the IIHS is definitely keen to blame muscle cars, it doesn't seem quite that simple.

[Images: Mitsubishi; IIHS]

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