WASHINGTON — Consumers who buy minicars to economize on fuel are making a big tradeoff when it comes to safety in collisions, according to an insurance group that slammed three minimodels into midsize ones in tests.
In a report prepared for release on Tuesday, the Insurance Institute for Highway Safety said that crash dummies in all three models tested — the Honda Fit, the Toyota Yaris and the Smart Fortwo — fared poorly in the collisions. By contrast, the midsize models into which they crashed fared well or acceptably. Both the minicars and midsize cars were traveling 40 miles per hour, so the crash occurs at 80 m.p.h.
The institute concludes that while driving smaller and lighter cars saves fuel, “downsizing and down-weighting is also associated with an increase in deaths on the highway,” said Adrian Lund, the institute’s president.
“It’s a big effect — it’s not small,” he said in a telephone interview.
Yet the institute did not quantify how many more highway deaths might be expected statistically from any increase in the use of minicars.
Dave Schembri, president of Smart USA, said the crash type chosen, a head-on collision, was a tiny fraction of accidents. He countered that the Smart Fortwo, with front and side airbags and electronic controls meant to help a driver avoid skidding, was very safe.
The institute usually tests cars individually but in this case paired the Honda Fit with a Honda Accord, the Toyota Yaris with a Toyota Camry and the Smart Fortwo with a Mercedes C-Class. (Both the Fortwo and the Mercedes are built by Daimler.)
The argument over weight versus safety is not a new one but took on greater significance when gasoline prices rose sharply last year, making minicars more popular. Consumers also seek out vehicles that burn less fuel so they will contribute less to global warming. Production of carbon dioxide, the main heat-trapping gas, is proportional to fuel use, and the Smart claims to be the highest-mileage car powered by gasoline on the American market.
When the institute crashed the Smart into the Mercedes C-Class sedan, the Smart, which weighs half as much as the sedan, went airborne and spun around one and a half times. The institute’s crash laboratory did not clock the speed of the rebound, but calculated that in a collision between cars of that weight, the sedan would slow down by 27 m.p.h. while the two-seater would change speed by 53 m.p.h., moving backward at 13 m.p.h.
The institute suggested steps that would further both fuel economy and safety rather than put them in conflict: cutting the speed limit and reducing horsepower. (Average horsepower is 70 percent higher in new cars now than it was in the mid-1980s, the institute said.)
But there is little support for either move. Some car efficiency experts have recommended making cars light but also large, with energy-absorbing crush zones. With several feet of car body in front of the driver, the energy of a crash can be dissipated and the suddenness of the change in velocity can be reduced, they say.
In any case, the statistical connection between vehicle weight and the risk to occupants is not completely clear. In 2002, the National Academy of Sciences said that steps by car manufacturers to reduce vehicle weight to comply with federal fuel economy standards had resulted in 1,300 to 2,600 additional deaths in 1993. But the number has not been updated.
Complicating matters, a statistical graph included in the institute’s study indicated that per million cars registered that were one to three years old in 2007, the death rate was higher for drivers in small cars than in minis, which are even smaller. One reason might be that the smallest cars are not driven as many miles on high-speed roadways, Mr. Lund said.