NHTSA crash tests

As part of its New Car Assessment Program, NHTSA scores its tests using a scale of one to five stars; the more the stars, the lesser the likelihood of injury or death. The IIHS uses a four-level scale: Poor, Marginal, Acceptable, and Good.

NHTSA reforms its star ratings

Starting in late 2010, NHTSA overhauled the way it conducts and scores crash tests. The changes are profound enough that the new star ratings for 2011 and subsequent models are not comparable to those assigned to 2010 and earlier models.

The change has two consequences. First, it will take a few years before NHTSA has tested enough vehicles to create a database useful for making broad comparisons. During that time the other main testing agency, the Insurance Institute for Highway Safety, www.hwysafety.org, will be the primary source consumers can consult for comparative crash-test information.

The second consequence is more important: NHTSA's new star-rating system should provide better information. Under the old system, most vehicles were racking up four or five stars in every category. The new system intends to be more discriminating.

It's expected that many cars that had been earning five stars will earn only three under the new system. That's because NHTSA is now factoring in more injury parameters, has added more tests, and is including data from dummies representing a small adult female instead of just an average-sized adult male.

NHTSA has also fundamentally changed the way it assigns the star ratings. Whereas under the old system the scores were based on a calculation of likelihood of serious injury, the new system will compare cars with each other. So it won't be enough for, say, a car to provide good head protection, to get a top score it will now have to provide better head protection than most other cars.

Key components of NHTSA's post-2010 crash-ratings:

• NHTSA will assign a single overall safety score that combines the results from front, side, and rollover tests. Front-crash results will weigh heaviest in the overall score.
• The 35-mph full-frontal crash test will use a new 5th-percentile (small adult female) dummy instead of a 50th-percentile "male" dummy on the passenger side.
• New measures for chest deflection, neck extension, and femur and foot injuries will be added to the front-crash score.
• The side-impact crash will include data from the head, abdomen, and pelvis, instead of just the chest. The rear passenger will be a 5th-percentile female dummy, instead of a 50th-percentile adult male, and include data from the head and pelvis.
• A sideways-into-pole test will be added, using the small adult female dummy.

Front crash

NHTSA's front-crash test accelerates a car straight into a rigid barrier at 35 mph, with the entire width of a vehicle's front end hitting the barrier. Instrument-bearing, seat-belted crash-test dummies in the two front seats record the level of crash forces on the head, neck, chest, and legs. Those measurements correlate with injury, but formerly only the head and chest results formed the basis of the star rating. Individual star ratings are assigned to the driver and the front passenger. Some automotive experts have criticized NHTSA's full-frontal, rigid-barrier test as unrealistic because such head-on crashes into a flat, solid wall are rare. Others argue that real-world or not, flat-barrier testing is a good way to gauge the effectiveness of the restraint systems, primarily the safety belts and air bags.

Side crash

NHTSA's side-impact test represents a vehicle struck on the left side by a 3,015-pound car traveling at 38.5 mph. Such a scenario mimics what could happen if you were hit on the side at an intersection. Individual side-impact star-rating scores are assigned to the driver and left-rear passenger. For pre-2011 models, only a chest-injury measure dictated the score. For 2011 and later models, the score factors in head, abdomen, and pelvis data as well.