The Insurance Institute for Highway Safety (IIHS) is funded by auto insurers to provide safety ratings for vehicles, in an attempt to reduce injuries in motor vehicle crashes. To learn more about how IIHS vehicle safety ratings work, you need to first understand what the IIHS tests for, how this testing is accomplished, and what the test scores mean when it comes to vehicle safety.

About the IIHS

Established in 1959, the IIHS performs a variety of tests on new and used model vehicles, rating them according to how they perform in these tests. Originally composed primarily of offset testing, the IIHS changed its testing to include overlap testing in 2012, which the agency thinks demonstrates the vehicle's structural strength better than the offset testing that it used before. In addition to safety testing, the IIHS releases annual Top Safety Picks for the best performing vehicles in various classes.

Types of safety tests performed

The types of testing that the IIHS performs includes both offset and overlap testing of frontal and side crashes. The IIHS also tests roof strength, head restraints, and seats.

Test 1: Frontal crash tests. Frontal crashes are the most common type of accidents that result in road fatalities.

This is a main area of IIHS testing in an effort to improve roadway safety. The two main breakdowns of frontal crash tests include moderate and small overlap testing.

  • Moderate overlap frontal testing uses a barrier a little over two feet tall. During the test, only 40 percent of the front of the driver's side of the vehicle strikes the barrier. The vehicle strikes the barrier made of an aluminum honeycomb material at 40 miles per hour (mph). The test dummy is positioned in the driver's seat, with the test designed to simulate a frontal offset crash between two vehicles weighing the same amount.

  • Small overlap frontal testing has the test vehicle traveling at 40 mph, and striking a five-foot-tall rigid barrier. This test is designed so that only 25 percent of the front driver's side of the vehicle hits the barrier, simulating what happens to a vehicle when striking an object such as a utility pole or tree. A test dummy is positioned in the driver's seat during small overlap frontal testing.

Test 2: Side crash tests. Side crashes are also a common occurrence during driving, accounting for roughly 25 percent of roadway deaths in the U.S.

Side crashes are hard to protect against, mainly because of the inability of the vehicle sides to absorb the energy from a crash due to lack of space. While the front and rear of a vehicle have adequate crumple zones to protect passengers, vehicle sides do not.

IIHS testing has played a part in pushing for the development of technologies designed to protect vehicle occupants from side impacts, including side airbags and the strengthening of a overall structure of vehicles.

For testing side impacts, the IIHS uses a 3,300-pound barrier, meant to represent an SUV, to impact the driver's side of the vehicle at 31 mph.

Smaller test dummies are used for side crash testing, due to the likelihood that women will suffer more serious injuries in the real world because of their smaller height compared to men.

Test 3: Roof strength test. Vehicle rollovers are also another hot topic discussion when it comes to accidents.

Vehicles are starting to incorporate electronic stability control systems into their design to help prevent this.

IIHS roof strength tests measure the ability of a vehicle roof to withstand roof impacts and maintain the survival space within.

To test this, IIHS testing uses a metal plate to push against the side of the roof at a slow and constant speed. Increasing force is applied, with the rating resulting from the point at which the vehicle roof is crushed at least five inches.

Test 4: Head restraints and seats test. While death is the worst outcome that can result from a vehicle crash, neck sprains and strains are the most frequently reported injury.

Using a special BioRID test dummy that has a realistic spine, the IIHS affixes vehicle seats to a test sled. The test sled is then accelerated and decelerated to simulate what happens to a vehicle in a crash situation.

The ultimate goal of the test is to simulate what happens with a vehicle's restraint system when involved in a crash from the rear, the most common collision type that causes neck injuries.

Test 5: Front crash prevention. In addition to the above safety tests, vehicles rated by the IIHS also gives a vehicle a rating in front crash prevention.

This rating is determined in large part by any systems included on a particular vehicle designed to help prevent a front crash, including Forward Collision Warning and Adaptive Cruise Control.

Also taken into account is whether a vehicle uses an autobrake system or not.

Vehicles undergo two forms of testing when determining their front crash prevention rating, the first at 12 mph and the second at 25 mph. Both tests reward a vehicle points determined by how quickly it warns drivers of any impending impact.

IIHS Safety ratings and what they mean

When purchasing a vehicle, you should check out the IIHS safety ratings to determine the vehicle's safety. Knowing that a vehicle has a Good or Poor safety rating is one thing, but you should also know exactly what the ratings mean.

Test 1: Frontal crash test ratings. With a majority of deaths from auto crashes resulting from a front impact, frontal crash testing plays a major role in helping develop better technology in vehicles today.

IIHS front crash testing is designed to test the overall structural integrity of a vehicle.

The IIHS uses a rating system consisting of rankings of Good, Acceptable, Marginal, and Poor. The highest rating a vehicle can receive in front crash testing is a rating of Good, with the worst rating being Poor.

Test 2: Side crash test ratings. Side crash testing determines how a vehicle fares when impacted by a vehicle from the side.

Side crash testing uses the same ratings as frontal crash tests, which include Good, Acceptable, Marginal, and Poor. Good is the best rating a vehicle can get in this type of testing, and Poor is the worst.

Test 3: Roof strength test ratings. While not as commonplace as frontal and side crashes, a vehicle landing on its roof is a possibility that the IIHS takes into account when testing the safety of a vehicle.

Using the same Good, Acceptable, Marginal, and Poor rating system, a vehicle garners a Good rating only if it can withstand a force of at least four times the vehicle's weight before the plate crushes the roof by five inches.

To qualify for an Acceptable rating, the strength-to-weight ratio falls to 3:5 and 2:5 for a moderate rating. Anything after that is considered a Poor rating.

Test 4: Head restraints and seats test ratings. While not designed to test the ability to prevent fatalities in a crash, head restraint and seat testing plays a part in preventing neck injuries, the most common result from an accident.

Head restraint and seat testing are comprised of a combination of two types of ratings. To get a Good rating, a vehicle's seats must have both a geometric and dynamic rating of Good.

  • The first is the geometric rating, which tests the effectiveness of the any head restraint system a vehicle uses. The head restraint system in a vehicle, which mainly consists of the headrest, is evaluated according to a seat's height relative to an average-sized male. The geometry of the head restraint is classified into one of four geometric zones, including Good, Acceptable, Marginal, and Poor, with Good being the most ideal and Poor being the least.

  • The second is the dynamic rating, which tests seats with a geometry rating of Good or Acceptable using a sled test to simulate a rear impact. The purpose of the test is to assess how well the seat reacts in a rear impact and how well it supports the torso, neck, and head of the specially-designed BioRID test dummy. The seat and head restraint are then given a rating of Good, Acceptable, Marginal, or Poor.

Test 5: Front crash prevention ratings. Scores in front crash prevention include Superior, Advanced, and Basic ratings.

To get a Superior rating, vehicles must also utilize an autobrake system and have to score at least five to six points on any testing. Vehicles that score at least two to four points on testing qualify for an Advanced rating, and those only scoring one point are rated as Basic.

IIHS top safety picks

In addition to providing safety ratings for vehicles, the IIHS also comes out with an annual list of Top Safety Picks. The vehicles on the list come from a variety of categories, including mini cars, small cars, midsize moderately-priced cars, midsize luxury/near luxury cars, large family cars, large luxury cars, small SUVs, midsize SUVs, midsize luxury SUVs, large SUVs, minivans, and large pickups.

To be picked for the Top Safety List for a given year, the vehicle has to earn a Good rating in all of the crashworthiness tests, and must also get a Basic rating in front crash prevention.

The difference between IIHS and the National Highway Traffic Safety Administration (NHTSA)

In addition to the IIHS, the NHTSA is a government agency that also performs safety tests on vehicles. The main difference between IIHS and NHTSA testing is that IIHS testing is offset. This offset testing only exposes 40 percent of the front of the vehicle being tested with the formable barrier. In this way, it tests the structural strength of the vehicle better than NHTSA testing does. NHTSA uses full frontal testing, which is more suited to the testing of seat belts and airbags. The difference in ratings is sometimes extreme, with some vehicles getting a good rating of 4 from the NHTSA, while the same vehicles rate poorly on their IIHS scores.

By reading up on a vehicle's IIHS safety ratings, you can determine if a car you want to purchase is safe enough for you. After you purchase your vehicle, you need to keep it maintained in order to remain safe on the road. You can accomplish this by having one of our expert mechanics perform a 75-point safety inspection.

This article originally appeared on as How Cars Get Safety Tested (How IIHS Safety Works).

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