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In the U.S. automotive market, two primary organizations conduct safety testing and rank the safety of our automobiles. Let’s look at NHTSA and IIHS crash testing and rankings to see how they compare.

The U.S. government conducts auto safety testing under the banner of the National Highway Traffic Safety Administration. The Insurance Institute for Highway Safety is a private, nonprofit organization funded primarily by large insurance companies. Both groups produce a measurement system for various safety evaluations, most notably crash tests. IIHS also puts the spotlight on poorly designed vehicles to motivate automakers to respond and make the vehicles safer for occupants involved in a crash.

The testing that NHTSA and IIHS do is similar but not the same. IIHS revises its ranking system and adds new tests more frequently than NHTSA does. IIHS also performs new preliminary testing and alerts automakers to testing that may be part of its official rankings in the future.

Types of NHTSA Crash Tests

NHTSA started crash testing cars in 1978, at the end of the dark ages of automotive safety. The initial focus was on frontal crashes. For this test a vehicle is crashed into a fixed barrier at 35 mph, simulating a head-on crash between two vehicles.

Since then, NHTSA has added several tests to their evaluations, including a side pole crash test that simulates a the driver’s side of a car hitting a utility pole or tree. The test vehicle is canted at a 75-degree angle into a pole about 10 inches in diameter. Results from all vehicles are comparable in this test because all vehicles are impacted by the same sized pole. This differs from most frontal and side crashes, in which larger vehicles are inherently safer.

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NHTSA performs other side impact safety tests as well. In the side barrier crash test, a 3,015-pound barrier (covered with crushable material that replicates the front of a vehicle) strikes the test vehicle from the side at 38.5 mph. Inside, instruments record the force of impact on crash-test dummies that substitute for real-life passengers.

Rollover crashes came into focus with the increased popularity of tall, tippy SUVs. Rollovers take the lives of more than a third of those killed in vehicle crashes each year. For rollover crash testing, NHTSA uses a machine that steers the vehicle in a “fishhook” maneuver. The idea is to test a vehicle's likelihood of turning over when the driver swerves the vehicle and then overcorrects their steering.

NHTSA’s five-star ratings system compiles the results of various tests into an easy-to-understand graphic that is on the Monroney sticker (window sticker) of every new car. It’s also available online.

Types of IIHS Crash Tests

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IIHS also performs the classic frontal impact test. However, the IIHS test is done at a higher speed and offsets the crash so that a barrier impacts 40 percent of the front, which makes it more difficult to earn a top score. IIHS also performs a more difficult frontal crash test, the small frontal overlap test, in which the vehicle is crashed into a rigid barrier at 40 mph, but only 25 percent of the vehicle strikes the hard barrier. This test was invented to test for a utility pole strike with just the corner of the car. These crashes can be surprisingly deadly. This is the most difficult test for a car to perform well in. As recently as 2016, pricey midsize cars like the Audi A4 still scored Poor (the worst possible rating) on this tricky test, while many lower-cost, smaller vehicles, like the Subaru Impreza, scored Good (the highest possible). IIHS also does side impact testing, roof crush testing, and rear-impact testing for headrest evaluations. Vehicles that achieve Good ratings in all of these crash tests earn a Top Safety Pick rating.

IIHS now includes active safety systems such as forward-collision prevention with automatic emergency braking in its ratings. Vehicles that earn Good rankings in all of the IIHS’ crash testing and also offer advanced active safety systems earn a Top Safety Pick+ rating. The “+” signifies the presence of the active safety gear. IIHS also plans to add headlight performance to its list of considerations.

Limits of Crash Testing

For practical purposes, both NHTSA and IIHS limit their testing. NHTSA says it does not conduct rear-impact testing because the group has, “… a limited budget and must concentrate its ratings on front and side-impact crashes that are responsible for the highest percentage of deaths and serious injuries.” However, the most common serious injury, and the injury that costs the U.S. the most in medical care, is whiplash from a rear impact.

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IIHS does a less expensive static test to determine a vehicle’s propensity to roll. That ignores suspension differences that can account for much of the rollover likelihood. IIHS also conducts its crash tests on the same side of the vehicle each time. In recent opposite-side testing of the small frontal overlap test, IIHS learned that almost all automakers strengthened only the side to be tested. This has prompted consideration to test both sides, which could double that test’s cost.

Future of Crash Testing

Testing continues to evolve as both NHTSA and IIHS add new tests to their evaluations. In the coming year, expect to see IIHS add headlight ratings to its requirements as well as passenger-side small frontal overlap testing. Bear in mind that each group’s ratings are most helpful when consumers compare vehicles of the same age, the same weight, and similar shape.