Is Bigger Really Safer?

Safety is arguably the most important factor people consider when choosing a vehicle.  There's a common assumption that bigger is safer, and that's what both the market and common sense seem to say.   Well, not so fast... a recent New York Times article reveals:

Collisions between an S.U.V., pickup or minivan and a car kill more people than car-to-car collisions, statistics show. When all types of crashes are considered, occupants of sport utilities and pickups actually have a higher death rate than car occupants. This is mainly because sport utilities and pickups are more likely to roll over when they strike another vehicle, a curb or a guard rail, or if they miss a turn or swerve.

In the limit, of course it's true that bigger is safer - a bicycle has little chance against a big truck.   But in between it's good design that matters most.   Drivers of lightweight racecars routinely walk away from 200 mph crashes.  Check out this video of a Smart Car hitting a concrete wall at 70 mph, another example showing that small cars can be safe cars.  (No, we're not shilling for the Smart Car - we're just making a point.)

While we're not advocating either small or big vehicles (they both serve a purpose), we are challenging assumptions.   Is bigger safer?

Comments

[Ken Fry]

Unfortunately, bigger really is better, in terms of real-world crashworthiness. It may be impressive to watch a small car smash into a barrier and retain some of its central structure. But, had there been a person in that Smart Car, the resulting G loading would probably not be survivable. (In many well-engineered cars a barrier crash is just barely survivable at half that speed, where there is one quarter the energy to dissipate.) Even in the lower speed crashes at the NHTSA facilities, the dummies don't always "live".

Although running a car into a barrier looks impressive, it is the equivalent of a head-on collision with a car of exactly the same mass and configuration, moving at the same speed -- something that virtually never happens in the real world. (In other words, the video demonstrates the effect of two Smart Cars colliding head-on, not the effect of a Smart Car colliding with Lincoln.) When two vehicles of different mass collide, the lighter one does not simply stop, as it does when hitting a barrier -- it is driven backwards by the larger one, making the accelerations encountered much higher. Both physics and NHTSA statistics demonstrate that lighter cars are not as crashworthy as larger ones, in head on crashes.

Confounding the weight comparison is the fact that the heavy vehicles (truck or truck-like) are engineered to different standards than the light ones. Old style SUVs and pickups had (and many still have) handling characteristics that are simply and clearly unsafe. They also are not engineered to be crashworthy (the Chevy Blazer being notorious). So, given bad handling, bad brakes, and bad structure, the big vehicles are unsafe. But it’s not their weight that makes them unsafe. When you crash your rollover-happy Explorer into your nicely engineered but lighter Volvo V40, chances are very good that the Volvo looses.

I think that most of the crash test sites have words to this effect.

I am all for promoting the use of smaller cars, and, in fact, still own a one-liter car. But I think our goals will not be well-served by painting an unrealistically rosy picture, any more than Bridgestone’s and Firestone’s goals were well-served by trying to hide the problems with the Explorers and their tires.