Buyers choosing the smallest cars for low price and high gas mileage could be endangering themselves and their passengers, says a major auto-safety researcher.

In new crash tests, the Insurance Institute for Highway Safety rammed three automakers’ smallest cars into their midsize models. Although the small cars had passed other IIHS tests, they flunked in collisions with larger but still-fuel-efficient sedans. “The safety trade-offs are clear,” IIHS President Adrian Lund says. “There are healthier ways to save gas.”
IIHS, funded by auto insurers, usually crashes cars into stationary barriers at 40 miles per hour. This time, it was car into car, each going 40 mph.

Barrier tests, in effect, show how a car holds up crashing into one like itself, Lund says. These tests show colliding with a larger car at the same effective speed as the barrier test.

IIHS picked three small cars that got its top rating of “good” in barrier tests. In these tests, they fell to “poor” The report comes as small cars take a larger share of U.S. new-vehicle sales. While R.L. Polk registrations show 13.8% of vehicles on the road are classed “small cars,” their share of new-car sales rose from 14.5% in 2006 to 18.1% last year, says Autodata.

“We’re hearing people say, ‘Everything gets a ‘good’ rating now, so I might as well buy a small car,’ ” Lund says. “A lot of people are forgetting that the laws of physics still hold” and even a little bit bigger still is safer.

The mileage trade-off may not be much. A Honda Fit, for instance, is rated 31 miles per gallon in city/highway driving. A larger Civic gets 29 mpg.

The IIHS tested:

• Fit vs. Accord. The Fit crash-test dummy registered severe leg injuries. The dummy’s head also slapped through the air bag and whacked the steering wheel.

• Toyota Yaris vs. Camry. Yaris nearly lost a door. Its driver’s seat tipped forward. The dummy’s head hammered into the steering wheel.

• Daimler Smart vs. Mercedes-Benz C-Class sedan. IIHS says the Smart “went airborne and turned around 450 degrees … a dramatic indication of the Smart’s poor performance, but not the only one.” Much of the interior was shoved into the crash dummy “from head to feet.”

Dave Schembri, president of Smart, says, “If you carry this to the nth degree, we’d all be driving 18-wheelers.” And, he says, fewer than 1% of crashes are as violent as the IIHS test.

Lund says the car vs. car tests are meant to mimic killer crashes, not fender benders. He also says that the only difference between the barrier test, in which Smart got a “good,” and the latest test is the size of the obstacle the Smart ran into.

Cynthia Sholander. of Fairfax, Va., praises Smart. She survived a horrific rear-end crash last October that sent her Smart sailing off Interstate 95, into trees, then bouncing back. Sholander says she suffered a concussion but no other injuries.