The Insurance Institute for Highway Safety (IIHS) front-crash tests are quite different from NHTSA's in that they’re designed to highlight the vehicle's structural integrity, as well as restraint performance. IIHS now conducts two series of front-crash tests, one that engages 40 percent of a vehicle’s front and a newer test, inaugurated in 2012, that uses a smaller overlap, engaging just 25 percent of the car’s front.
Both simulate what would happen if two cars of the same weight and type crashed head-on, partially overlapping. The older test, with the 40-percent offset, engages the portion straight ahead of the driver. The newer test is more like a head-on crash where two cars hit left-headlight to left-headlight or a single-vehicle crash into a fixed object like a utility pole or tree. These are very different from the full-width crash NHTSA uses. Both the IIHS front-crash scenarios use an impact speed of 40 mph instead of 35 mph; and only the left front of the car hits the barrier. The 40-percent overlap test uses a deformable barrier while the 25-percent overlap test uses a rigid barrier.
One effect of the new small-overlap test is that the vehicle tends to rotate around the point of impact as the crash proceeds. Since occupants then move to the side as well as forwards, the test poses new challenges to some safety-belt and air-bag systems. Even though this is a frontal crash, the side-impact air bags may need to deploy as well. Moreover, many cars are not designed to withstand a corner hit as well as they handle an impact that engages a wider portion of the front. There can be more intrusion into the driver’s foot-well, which can cause severe leg injuries.
Both of the IIHS frontal tests are more stringent than NHTSA's because the speed is higher and the crash energy is concentrated on a smaller area. In both, an instrument-equipped crash dummy in the driver's seat records forces to the head and neck, chest, legs, and feet. Vehicles are rated as Good, Acceptable, Marginal, or Poor based on what happens to vehicle structure, as well as forces on the dummies.
The IIHS side-impact test is more severe than NHTSA's. The test uses a heavier striking barrier at 3,300 pounds, compared with NHTSA's at 3,015 pounds. Further, the IIHS barrier strikes higher up on the tested vehicle to simulate a car being hit on the side at 90 degrees by a typical-height SUV or truck. The IIHS bases its scores on head, neck, chest, abdomen, pelvis, and leg injury.
The two dummies in the IIHS side-crash test represent a small adult female or a 12-year-old adolescent. One is the driver, the other a left-rear passenger. Other crash tests performed by NHTSA and the IIHS use a dummy that simulates an average-sized adult male.
See videos of how cars perform in IIHS' front and side crash tests.
IIHS rear-impact evaluations
Though common, not many rear-impact crashes are fatal. But they do cause many injuries, especially whiplash trauma to the neck. The IIHS evaluates rear impacts with physical inspections and crash testing. The crash test, which is conducted with the vehicle seat attached to a moving sled, simulates a rear-end crash about equivalent to a stationary vehicle being struck at 20 mph by a vehicle of the same weight.
The key to rear-impact protection is head-restraint design. Restraints need to be high enough and positioned close enough to the back of the head to cradle an occupant's head in a rear collision. Those restraints that are clearly too low or ill-designed automatically receive a Poor rating from IIHS, while those with a chance of providing decent protection are crash-tested.