DETROIT » The four-door Mini Cooper Countryman was the only one of 12 cars to earn a top rating of "good" in new frontal crash tests.

The Nissan Leaf, Nissan Juke, Fiat 500L and Mazda5 wagon all fared worst in the tests performed by the Insurance Institute for Highway Safety, an Arlington, Va.-based safety group that’s funded by insurers.

The Chevrolet Volt, Ford C-Max, Mitsubishi Lancer, Scion FR-S and Subaru BRZ all got the second-highest rating of "acceptable." The Hyundai Veloster and Scion xB were a notch below that, with "marginal" ratings.

The small overlap front crash test, introduced in 2012, replicates what happens when 25 percent of a car’s front end strikes a rigid object at 40 miles per hour. It’s a difficult test because a small area of the car’s front end must absorb and manage the energy from a severe, high-speed crash.

To earn a "good" rating, a car must keep the cabin around the occupants largely intact and protect them with a combination of seat belts and air bags, the institute said. When a car’s cabin collapses, as it did in the crash tests of the Juke, Leaf, 500L and Mazda5, it can move the seats and air bags out of place, increasing the risk of injuries.

The institute said 19 of the 32 small cars it has now tested have earned "good" or "acceptable" ratings on the small overlap test. The institute said the Mazda5 was among the worst performers it has tested. Its side air bags didn’t deploy at all and its driver’s side door unlatched, which shouldn’t happen during a test.

In a statement, Mazda pointed out that the Mazda5 has earned "good" ratings on other IIHS tests, including a front moderate overlap test and a roof strength test. It earned a "marginal" rating in a side-impact crash test performed by the institute.

"We take these results seriously, and are studying the results of these IIHS tests as we consider the design of future vehicles," the company said.

The Chevrolet Volt was the only car in the group to be labeled a "Top Safety Pick Plus," because it has an optional front crash prevention system. The C-Max Hybrid, Countryman, Mitsubishi Lancer, Scion FR-S and Subaru BRZ earned "Top Safety Pick" awards because they don’t have front crash prevention systems.

To be a top safety pick, vehicles must earn "good" or "acceptable" ratings for small overlap protection and "good" ratings on the institute’s other four crash tests.