The Insurance Institute for Highway Safety (the place that crashes cars into walls for science) recently ran a dozen popular small cars, including the Chevy Volt, Ford C-Max Hybrid, Mini Cooper Countryman, and the Mazda 5, through its “small overlap” front crash test, where only the front corner of the vehicle is involved in a collision. While several of the tiny cars had okay results, only one earned an overall “good” rating from the IIHS.

The Mini Cooper Countryman was the only small car among the dozen tested to earn that overall “good” rating in the overlap test, which was introduced in 2012 to simulate collisions where a car strays across the median and hits an oncoming vehicle, or where cars smash into objects like trees or poles.

For years, car makers were building vehicles to pass the IIHS head-on frontal crash tests, in which the full front end of a vehicle collides with a solid object, but the small overlap test shows that not all car makers have been thinking about what happens when it’s just the corner of the vehicle.

“In the small overlap test, the main structures of the vehicle’s front-end crush zone are bypassed, making it hard for the vehicle to manage crash energy,” explains the IIHS. “The occupant compartment can collapse as a result.”

To earn a “good” rating in the overlap test, the car’s occupant compartment must resist intrusion, its safety belts must prevent the driver from pitching too far forward, and its side curtain airbags must provide enough forward coverage to cushion a head at risk of hitting the dashboard or window frame or things outside the vehicle.

“The Mini Cooper Countryman gave a solid performance,” says Joe Nolan, the Institute’s senior vice president for vehicle research. “The Countryman’s safety cage held up reasonably well. The safety belts and airbags 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 IIHS points out that the small overlap rating for the Countryman — the 4-door version of the Mini Cooper — doesn’t apply to the two-door model, which hasn’t been tested.

Four other small cars — the Volt, the C-Max Hybrid, Mitsubishi Lancer, and the Scion xB — showed minimal damage to their respective crash test dummies, but fell short of an overall good rating for concerns about their structures or restraint systems. However, all but the Scion xB are still considered “Top Safety Picks” by the IIHS.

Of greater concern are the four cars earning “poor” overall ratings in the overlap test — the Fiat 500L, Mazda 5, Nissan Juke and Nissan Leaf.

IIHS’s Nolan says that “Collapse of the occupant compartment is the downfall” for these four vehicles. “A sturdy occupant compartment allows the restraint systems to do their job, absorbing energy and controlling occupant motion.”

Test showed that the structure of the Fiat 500L was being pushed into the driver’s survival space, “knocking the steering wheel back and to the right of the driver,” which puts the airbag out of position, meaning the dummy’s head slid off to the left side.

According to the IIHS, the Mazda 5 is among the worst-performing cars in the small overlap test, along the 2014 Kia Forte, and the 2012 Prius v.

“When we tested the Mazda 5 we saw a host of structural and restraint system problems. Parts of the occupant compartment essentially buckled, allowing way too much intrusion,” Nolan says.

The test dummy in the Mazda 5 showed high risk of injuries to the left thigh and left lower leg. The steering wheel moved to the right, meaning the dummy’s head barely contacted the front airbag before sliding off the left side.

Additionally, the safety belt failed to keep the dummy’s head and torso from moving too far forward. The dummy’s head made contact with the left side of the dashboard.

Even worse, the side curtain airbag didn’t deploy at all, says the IIHS and the driver door unlatched during the test, putting the driver at risk of being ejected.

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