NHTSA and IIHS Crash Test Scores Explained

Manufacturers like Mercedes-Benz and Volvo have long been testing the protection of their cars. 1 photo
Photo: Daimler AG
Almost 100 years ago, car passengers faced risks of death even in a minor – by today's standards – fender bender. Automobile safety has evolved so much in recent times that it is possible to escape with minor or even no injuries at all from a 80 km/h (50 mph) head-on crash.
In the past five decades, a few independent organizations have started performing well-established crash tests of which results have now become a very important part in the buying decision of almost every new car customer. This article will try to explain the criteria by which each American crash testing organization achieves its results.


The oldest government sponsored crash tests in the US were first conducted by the National Highway Traffic Safety Association (NHTSA) in 1978. A division of the US Department of Transportation, the NHTSA association began a series of test which are now referred as the New Car Assessment Program (NCAP), or “government 5-star ratings”. The second American association to perform large scale crash testing was the Insurance Institute for Highway Safety (IIHS), which is an organization sponsored by insurance companies. They began wrecking cars in the name of science and safety in 1995.

Although both organizations are crash testing cars for a similar reason, each has a different procedure to achieve desired results. Both perform frontal and side crash tests, although conduced differently. Plus, the IIHS assesses seat and head restraints in rear crashes, bumpers in low-speed fender benders, while the NHTSA also has a rollover crash test.

Not every car on the market is tested, but vehicles to be voluntarily rammed into a wall are usually chosen following a customer popularity factor. We'll now have a look at how each crash test is conducted, so that car customers everywhere should better understand the reasoning behind each result.

Frontal Crash Test (NHTSA)

As we mentioned before, the NHTSA and IIHS each have their own way of conducting the tests. Let's first look at the NHTSA one. In the frontal test, two average male sized crash test dummies are placed in the driver and front-passenger seat and are secured by the car's compulsory seatbelts. The vehicle is then rammed head-on into a fixed barrier at a speed of 35 mph (56 km/h). This speed tries to recreate the impact of two similarly weighed vehicles colliding each other head-on at the aforementioned speed.

The force inflicted upon the high-tech dummies is then measured, and the NHTSA dudes give the car a star rating based on each dummie's chance of serious injury, expressed in percentages. By the way, by “serious injury” the NHTSA means an injury that requires immediate hospitalization and may be life-threatening, so a broken finger nail doesn't count. The star ratings used by the NHTSA make everything look like a game of Russian roulette, but here they are anyway:

5 Stars (meaning 10% or less chance of serious injury)
4 Stars (meaning 11-20% chance of serious injury)
3 Stars (meaning 21-35% chance of serious injury)
2 Stars (meaning 36-45% chance of serious injury)
1 Star (meaning 46% or greater chance of serious injury)

Frontal Crash Test (IIHS)

The IIHS organization conducts two slightly different frontal tests. In the first, the vehicle is hitting a deformable barrier in an off-set manner, meaning that only the driver's front end is struck. The test is conducted at 40 mph (64 km/h), and around 40 percent of the car's front end impacts the deformable wall. In the second one, called the small overlap-front test, only 25 percent of the vehicle's front end strikes a non-deformable barrier at 40 mph (64 km/h).

Trying to be even more special, the IIHS doesn't use stars to rank the vehicle tested. Instead, it uses kindergarden-like ratings: Good, Acceptable, Marginal and Poor. On top of that, cars that do exceptionally well in all crash tests are giveon one of two awards, each being more important than the other: Top Safety Pick or Top safety Pick + for the best performing cars.

Unlike the NHTSA tests, these ratings do not correlate to a chance of injury because the IIHS is assessing how the overall vehicle structure performs, and not just the occupants. Considering how different the two frontal tests are to each other, both organizations reckon that the tests do not compete, but instead complement each other.

Side-Impact Crash Test (NHTSA)

In the NHTSA test, two crash test dummies that represent average-sized men are put in the car. One sits in the driver seat and one in the rear, just behind the driver. The vehicle is then struck by a 3,015-pound (1368 kg) barrier travelling at 38.5 mph (62 km/h). Computers connected to the dummies measure the force of the impact to the head, neck, chest and pelvis, but the star ratings are used to show only the chance of serious injury to the chest. The NHTSA separately reports in a “safety concern” if there is any likelihood of serious head injuries. These are the Side-Impact Tests ratings:

5 Stars (meaning 5% or less chance of serious injury)
4 Stars (meaning 6-10% chance of serious injury)
3 Stars (meaning 11-20% chance of serious injury)
2 Stars (meaning 21-25% chance of serious injury)
1 Star (meaning 26% or greater chance of serious injury)

Side-Impact Crash Test (IIHS)

Naturally, the IIHS does the side-impact test a little bit different. First of all, the two dummies represent small women or children, but they are placed just like in the NHTSA test. Second of all, the deformable barrier is differently shaped, weighs 3,300 pounds (1497 kg) and is taller than the one used by the NHTSA.

After being slammed into the side of the vehicle at 31 mph (50 km/h), computers measure the potential of serious injuries to the head, neck, chest, abdomen, pelvis and femur of the crash test dummies. The test rating also comprises of marks from “Good” to “Poor” to asses the severity of the accident on the dummies. Because this test is so severe, it practically emulates an accident in which the “victim” car is slammed by a full-size SUV.

Rollover Test (NHTSA)

For the moment, only the NHTSA is conducting rollover tests in the United States. Put into action since 2004, the test actually comprises of static test and a motion one. The motion test consists of a pre-weighed vehicle which simulates being loaded with five passengers and a full tank of fuel. the car is then put to simulate and emergency lane change while computers are measuring the movement of the tires. If two tires simultaneously lift at least 2 inches (5.1 centimeters) off of the ground, the car is considered to be in the risk of rolling over. The results are rated just like the other tests:

5 Stars (meaning 10% or less risk of rolling over)
4 Stars (meaning 10-20% risk of rolling over)
3 Stars (meaning 20-30% risk of rolling over)
2 Stars (meaning 30-40% risk of rolling over)
1 Star (meaning 40% or greater risk of rolling over)

Rear Crash Test (IIHS)

To complement the NHTSA again, currently the IIHS is the only US organization to asses rear crash protection. Just like in the NHTSA rollover test, both static and motion tests are required for the IIHS to evaluate the rear crash protection. In the static one, a crash test dummy sized as an average adult male is put in the driving seat which is tilted at about 25 degrees. The head restraint should be 3.5 inches or less (8.9 centimeters) from the top of the head and less than four inches (10.1 centimeters) from the back of the head. If it is adjustable (which in most cases is), measurements are taken in both the down position and the most favorable position. Just like in the other IIHS tests, a rating which ranges from “Good” to “Poor” is given.

Only the restraints which get the “Good” or “Acceptable” ratings move on to the motion test, in which the same dummy gets to sit in the driver's seat. The vehicle is then put on a sled which simulates the car being slammed by another similarly weighing vehicle at 20 mph (32 km/h) from the rear. Computers then measure the impact forces that acted on the head, neck, spine and torso. A combined overall rating between the static and the motion test is then achieved.

Low-Speed Bumper Test (IIHS)

Another crash test which is skipped by the NHTSA but conducted by the IIHS is the low-speed bumper test. A vehicle is crashed two times at 5 mph (8 km/h) into a flat barrier (with both the front and the rear bumpers), one time into an angled barrier with the front bumper and then into a short pole with the rear bumper. The usual “Good” to “Poor” ratings are then given, only this time they are based on the accident repair costs.

In another similar Auto Guide we will talk about two other major international crash testing organizations: the EuroNCAP and the down under ANCAP.
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About the author: Alex Oagana
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Alex handled his first real steering wheel at the age of five (on a field) and started practicing "Scandinavian Flicks" at 14 (on non-public gravel roads). Following his time at the University of Journalism, he landed his first real job at the local franchise of Top Gear magazine a few years before Mircea (Panait). Not long after, Alex entered the New Media realm with the project.
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