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New IIHS crash test aims to improve passenger safety

Wednesday, August 15, 2012 - 20:44
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Most modern cars have safety cages built to withstand head-on collisions and moderate overlap frontal crashes with little deformation. At the same time, crush zones help manage crash energy to reduce forces on the occupant compartment. The main crush-zone structures are concentrated in the middle 50 percent of the front end. When a crash involves these structures, the occupant compartment is protected from intrusion, and front airbags and safety belts can effectively restrain and protect occupants.

Small overlap crashes are a different story. These crashes primarily affect a car’s outer edges, which aren’t well protected by the crush-zone structures. Crash forces go directly into the front wheel, suspension system and firewall. It is not uncommon for the wheel to be forced rearward into the footwell, contributing to even more intrusion in the occupant compartment and resulting in serious leg and foot injuries. To provide effective protection in small overlap crashes, the safety cage needs to resist crash forces that aren’t tempered by crush-zone structures. Widening these front-end structures also would help.

“These are severe crashes, and our new test reflects that,” Lund says. “Most automakers design their vehicles to ace our moderate overlap frontal test and NHTSA’s full-width frontal test, but the problem of small overlap crashes hasn’t been addressed. We hope our new rating program will change that.” Luxury and near-luxury cars were first to the test because these models typically get advanced safety features sooner than other vehicles, Lund says.

Vehicle test performance varied widely in the three rating categories: structure, restraints and kinematics, and dummy injury measures. The majority of the cars had lots of occupant compartment intrusion, which contributed to their low overall rating. Occupant motion varied greatly as well, with the dummy missing the airbag in some cases. In others, safety belts allowed the dummy’s head and torso to move too far forward toward the A-pillar. Forces measured on the dummy indicated high risk of injury for the legs and feet in several vehicles.

Structurally, the Volvo S60 was best. With only a few inches of intrusion, the occupant compartment looked much the same as it did in a moderate overlap test. Reinforcement of the S60’s upper rails and a steel cross member below the instrument panel helped to keep the safety cage intact. Volvo has performed similar small overlap tests as part of its vehicle safety development process since the late 1980s, taking the results into account when designing new models.

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