(MCT) -- In crash tests of small cars, the little Mini Cooper Countryman turned in a big performance - it was the only vehicle in a group of 12 to win the top rating from the Insurance Institute for Highway Safety.
The electric Nissan Leaf short-circuited, and the Mazda5 joined a select group of the insurance institute's worst tested vehicles.
All of the cars went through the group's small overlap front crash test, in which 25 percent of a car's front end on the driver's side strikes a 5-foot-tall rigid barrier at 40 mph, with test dummies onboard. It simulates a wreck in which the front corner of the car hits another car or solid object.
Such crashes account for nearly a quarter of frontal crashes involving serious or fatal injury, according to the institute.
"The Countryman's safety cage held up reasonably well," said Joe Nolan, the institute's senior vice president for vehicle research. "The safety belts and air bags worked together to control the test dummy's movement, and injury measures indicate a low risk of any significant injuries in a real-world crash this severe."
The institute gave the Countryman its "good" rating for the test but said the designation does not apply to the two-door Mini, which hasn't been tested.
Compact cars make up more than 18 percent of California's new-car sales - the largest segment of the market and more than any other state, according to auto information company Kelley Blue Book.
In the test, researchers study whether the occupant compartment resists intrusion of collapsing car parts and structures. Using test dummies, they check on whether safety belts prevent a driver from pitching forward and ascertain whether side-curtain air bags block a head from hitting the dashboard, window frame or objects outside the vehicle.
"A sturdy occupant compartment allows the restraint systems to do their job, absorbing energy and controlling occupant motion," Nolan said.
The Fiat 500L, Mazda5, Nissan Juke and Nissan Leaf all failed the test and earned "poor" ratings because of the collapse of their occupant compartments, he said.
The Mazda5 joins two cars tested last year - the 2014 Kia Forte, another small car, and the 2012 Prius v, a hybrid station wagon - as the three worst-performing models ever evaluated in the small overlap test, the institute said
"When we tested the Mazda 5 we saw a host of structural and restraint system problems," Nolan said. "Parts of the occupant compartment essentially buckled, allowing way too much intrusion."
In a statement, Mazda noted that in addition to the "poor" rating for the most recent test, the Mazda5, an older vehicle introduced in 2005, received a "marginal" rating in the institute's side impact test.
"We take these results seriously, and are studying the results of these IIHS tests as we consider the design of future vehicles," the automaker said.
Of the two electric vehicles in the group, the Chevrolet Volt did best.
"Electric vehicles have a unique challenge in the small overlap test because of their heavy batteries. The Volt performed reasonably well, earning an acceptable rating, while the Leaf struggled," Nolan said.
The Volt's interior held together and injury measures taken from the dummy indicated a low risk of significant injuries to a human in such a crash.
But a Leaf driver would be in trouble. The instrument panel, parking brake pedal and steering column all pushed back toward the driver, creating the potential for leg and thigh injuries.
Nissan said in a statement that it was supportive of consumers having access to crash test information and that it "will continue to review these and other results from the IIHS 'small overlap frontal test' as we seek opportunities for improvement."
Among the other cars tested, the Ford C-Max hybrid, the Mitsubishi Lancer, Scion FR-S and Subaru BRZ earned "acceptable" ratings.
The Hyundai Veloster and Scion xB earned "marginal" ratings.
Testing conducted by the insurance institute is important, said Clarence Ditlow, executive director of Center for Auto Safety, because it complements crash tests and research by the National Highway Traffic Safety Administration.
The institute's research, Ditlow said, demonstrates that so-called active safety systems, such as the forward collision warning systems on some new cars, are preventing crashes.
Moreover, Honda, Toyota and other manufacturers have designed or redesigned models to perform better in the institute's tests.
"Our fundamental position on both safety standards and testing is that unless you set standards and have test procedures, the manufacturers have no incentive to upgrade their vehicles," Ditlow said.
Others also look at the institute's ratings. Consumer Reports pulled its recommendation for Toyota's Camry, Prius v and RAV4 sport utility vehicle and the Audi A4 after they received "poor" ratings on the test.
After Toyota strengthened the frame of the sedan, the 2014 model won an acceptable rating from the institute, and Consumer Reports restored its recommendation.
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