Park a diminutive Nissan Versa next to a massive Ford Expedition, and the size difference between them implies an apparent advantage in a head-on collision. However, recent research from the Insurance Institute for Highway Safety (IIHS) reveals that the assumption “bigger is always safer” has its limits.
The Impact of Vehicle Weight on Safety
For vehicles weighing less than the fleet average, every additional 500 pounds significantly reduces the risk of fatal crashes for occupants. However, once a vehicle surpasses the fleet average weight, additional pounds provide diminishing returns in terms of occupant safety.
Lighter-than-average vehicles: Adding 500 pounds improves occupant survival rates substantially.
Heavier-than-average vehicles: Extra weight offers little additional protection while increasing the danger to occupants of other vehicles.
IIHS President David Harkey summarized these findings: “For American drivers, the conventional wisdom is that if bigger is safer, even bigger must be safer still. These results show that isn’t true today. Not for people in other cars. And — this is important — not for the occupants of the large vehicles themselves.”
Improved Crash Compatibility Over Time
For years, larger SUVs and pickups posed an increased threat to smaller cars, largely because their force-absorbing structures were not aligned. This misalignment often caused them to override smaller vehicles, bypassing their crumple zones.
A major shift occurred in 2009 when automakers voluntarily modified the front-end designs of SUVs and pickups, aligning them better with the safety structures of passenger cars. In addition, side airbags and reinforced frames became standard, significantly reducing fatalities in side-impact crashes.
Changing Risk Levels in Two-Vehicle Crashes
IIHS researchers examined crashes involving 1- to 4-year-old vehicles over two periods: 2011-16 and 2017-22. The results highlight how structural improvements have changed the safety landscape:
2011-16: Car occupants were 90 percent more likely to die in crashes with SUVs over 5,000 pounds compared to crashes with other cars.
2017-22: That likelihood dropped to just 20 percent as SUV designs became more compatible with smaller vehicles.
Pickup trucks: Though improved, they remain the most hazardous. In the earlier period, pickups were 2.5 times more likely than cars to cause fatalities in crash partners. By 2017-22, that number dropped to just under twice as likely.
While SUVs and pickups are no longer as deadly to smaller cars as they once were, their weight still plays a crucial role in crash outcomes.
The Role of Weight in Crash Outcomes
The study highlights the trade-offs associated with vehicle weight:
Adding 500 Pounds to Vehicles Below 4,000 Pounds:
- Cars: 17 fewer driver deaths, minimal impact on crash partners
- SUVs: 13 fewer driver deaths, slight increase in crash-partner fatalities
- Pickups: Negligible reduction in driver deaths, four additional fatalities in crash partners
Adding 500 Pounds to Vehicles Above 4,000 Pounds:
- Cars: Two additional driver deaths, two more crash-partner deaths
- SUVs: Negligible change for driver, two additional crash-partner deaths
- Pickups: Slight driver safety benefit, but seven additional crash-partner deaths
Sam Monfort, IIHS senior statistician and lead author of the study, explained: “There’s nothing magical about 4,000 pounds except that it’s the average weight. Vehicles that are heavier than average are more likely to crash into vehicles lighter than themselves. What this analysis shows is that choosing an extra-heavy vehicle doesn’t make you any safer, but it makes you a bigger danger to other people.”
The Shift in Vehicle Weight Trends
Changes in vehicle design have influenced overall weight distribution in recent years:
The average U.S. car weight increased slightly from 3,277 pounds (2011-16) to 3,308 pounds (2017-22), moving closer to the 4,000-pound fleet average.
The percentage of SUVs over 5,000 pounds dropped from nearly 11 percent to 7.4 percent over the same periods.
Pickups, however, have continued to grow, with 97 percent of late-model pickups now exceeding 4,000 pounds, up from 91 percent previously.
Harkey emphasized the significance of these changes: “It’s a positive development that cars and SUVs are now closer in weight. These numbers show that transitioning to lighter pickups could have big benefits too, especially since many drivers don’t use their trucks for carrying heavy payloads.”
Weighty Matters: Safer or Not?
While larger vehicles do offer protection up to a point, excessive weight brings diminishing returns for occupant safety and poses an increased risk to others on the road. Improvements in vehicle design have mitigated some dangers associated with size disparities, but the key takeaway is clear: balance is crucial. Choosing a vehicle solely for its heft does not guarantee superior safety and may increase risks for everyone on the road.
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