IIHS crash tests show car size matters

Whenever you select a car to buy, you make tradeoffs. With a pickup, for instance, you typically sacrifice ride comfort and ease of access for the sake of utility. Similarly, when you pick a small car, you naturally expect good fuel economy, maneuverability and a low price, for which you usually forego passenger space, quietness and ride comfort. Intuitively, you know you may also be compromising some crash safety.

It's long been known that in a duel between a small, light vehicle and a big, heavy one that the big car usually wins, based solely on the laws of physics. Just how bad it is for small-car occupants has been less clear. Now the Insurance Institute for Highway Safety (IIHS) has started to address that question with offset-frontal crash tests pitting three subcompact cars—the Honda Fit, Smart ForTwo, and Toyota Yaris—against larger ones from the same automaker. The results aren't so good for occupants of the small cars. The three subcompacts tested all rated a "Poor," meaning that serious or fatal injuries to the driver were likely. (See videos of IIHS crash tests.)

Most modern cars, even small ones, show good results in independent crash tests, and the three subcompacts tested all rated "good" in the IIHS's conventional offset-frontal crash tests.

It's important to understand that the frontal crash tests published by the government and the IIHS simulate a situation where a car crashes head-on into an identical car. (Learn how the government and IIHS conduct crash tests.) That's a reliable way to gauge many aspects of crashworthiness, but in real life most car-to-car collisions involve two vehicles of different size and weight. In terms of probability, it's less likely that two subcompacts will "meet" head-on, especially here in the U.S. where a majority of the vehicles on the road are midsized family sedans, SUVs, and pickup trucks. By the way, this is not the case with IIHS side-impact tests, since those crashes simulate a car being hit amidships by a midsized SUV, regardless of the size of the vehicle being hit.

In this demonstration, the Honda Fit was pitted against the Accord, the Smart ForTwo against the Mercedes-Benz C-Class and the Toyota Yaris against the Camry. The Fit's driver dummy sustained serious leg and moderate head injury. The Smart was thrown in the air, and its driver sustained injury to the head and both legs. The Yaris dummy recorded serious damage to the head, neck, and right leg. Meanwhile, the Accord and C-Class maintained their "Good" standing.  The Camry's driver dummy posted forces equating with "Acceptable." That somewhat unexpected result came about because of the Camry's driver's seat tipping up and the dummy's head hitting the steering wheel through the air bag. (Compare safety equipment on today's cars.)

Despite these findings, there are still good reasons to buy a mini or a subcompact car if it fits your needs, including cost of ownership, maneuverability, and fuel economy. The choice here is not about a safe car and an unsafe car but about minimizing risk. While the smallest cars generally have a worse experience in all kinds of collisions, both car-to-car and single-vehicle crashes, there are still significant differences between the best and the worst, and you should choose one with the best crash-test scores.

The IIHS, as well as automakers, point out that it is technically possible to make the smallest cars more crashworthy than they are. The difficulty is that it would require a much greater use of high-strength steel. This, in turn, adds cost, which undermines one of these cars' main appeals. Ultimately, as more subcompacts join the fleet in coming years, including the Ford Fiesta, Fiat 500, and Scion iQ buyers need to bear the crash-protection tradeoff in mind.

—Gabe Shenhar

Learn more about car safety in "Crash Test 101" and "Rollover 101."