IIHS: Small Cars More Dangerous
Three front-to-front crash tests, each involving a microcar or minicar into a midsize model from the same manufacturer, show how extra vehicle size and weight enhance occupant protection in collisions. These Insurance Institute for Highway Safety (IIHS) tests are about the physics of car crashes, which dictate that very small cars generally can't protect people in crashes as well as bigger, heavier models.
"There are good reasons people buy minicars," says IIHS president Adrian Lund. "They're more affordable, and they use less gas. But the safety trade-offs are clear from our new tests. Equally clear are the implications when it comes to fuel economy. If automakers downsize cars so their fleets use less fuel, occupant safety will be compromised. However, there are ways to serve fuel economy and safety at the same time."
IIHS didn't choose SUVs or pickup trucks, or even large cars, to pair with the micro and minis in the new crash tests. The choice of midsize cars reveals how much influence some extra size and weight can have on crash outcomes. IIHS chose pairs of 2009 models from Daimler, Honda, and Toyota because these automakers have micro and mini models that earn good frontal crashworthiness ratings, based on the institute's offset test into a deformable barrier. Researchers rated performance in the 40 mph car-to-car tests, like the front-into-barrier tests, based on measured intrusion into the occupant compartment, forces recorded on the driver dummy, and movement of the dummy during the impact.
The Honda Fit, Smart Fortwo, and Toyota Yaris are good performers in IIHS' frontal offset barrier test, but all three are poor performers in the frontal collisions with midsize cars.
Size and weight affect injury likelihood in all kinds of crashes. In a collision involving two vehicles that differ in size and weight, the people in the smaller, lighter vehicle will be at a disadvantage. The bigger, heavier vehicle will push the smaller, lighter one backward during the impact. This means there will be less force on the occupants of the heavier vehicle and more on the people in the lighter vehicle. Greater force means greater risk, so the likelihood of injury goes up in the smaller, lighter vehicle.
Crash statistics confirm this. The death rate in 1-3-year-old minicars in multiple-vehicle crashes during 2007 was almost twice as high as the rate in very large cars.
The death rate per million 1-3-year-old minis in single-vehicle crashes during 2007 was 35 compared with 11 per million for very large cars. Even in midsize cars, the death rate in single-vehicle crashes was 17 percent lower than in minicars. The lower death rate is because many objects that vehicles hit aren't solid, and vehicles that are big and heavy have a better chance of moving or deforming the objects they strike. This dissipates some of the energy of the impact.