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Decoding car safety ratings

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    When you’re out car shopping, there are several things you might consider in the cars you’re looking at — speed, handling, storage space and comfort, just to name a few. One of the most important things to look at, however, is the car’s safety rating. Modern cars come with standard safety features, but due to differences in design and manufacturing, some cars are rated safer than others. Car safety ratings are designed to give customers a standardized metric that they can use to compare cars. Let’s learn more about what these ratings mean and how they’re assigned.

    Two types of car safety ratings

    The idea of creating standardized car safety ratings began in the late 1970s as a way to give consumers more clarity on how different vehicles would perform in an accident or other adverse event. Safety ratings typically involve conducting several different collision tests and assigning the vehicle an overall grade based on the results.

    Although some manufacturers conduct their own safety and collision testing, there are two main organizations that hand out vehicle safety ratings within the United States. Each has its own methodology and rating system.

    National Highway Traffic Safety Administration

    The National Highway Traffic Safety Administration (NHTSA) is a government agency operating under the broader jurisdiction of the Department of Transportation. NHTSA safety testing began with frontal collisions in the late 1970s and has since evolved to include a few other items. Vehicle safety ratings are assigned along a five-star system, with five stars being the best possible rating. NHTSA safety testing is conducted yearly on several of the best-selling cars on the market. Not every car is tested, however, and the cars that are tested annually may vary from year to year.

    Insurance Institute for Highway Safety

    The Insurance Institute for Highway Safety (IIHS) is an independent, non-profit organization represented by most of the major players in the U.S. insurance market. As part of their ongoing commitment to reducing deaths, injuries and property damage from car accidents, IIHS conducts extensive research into car safety.

    IIHS began conducting a variety of collision tests in the early 1990s, which differ from the tests conducted by the NHTSA (more on this below). Depending on the results of these tests, the vehicle is assigned a car safety rating of Good, Acceptable, Marginal, or Poor. Much like the NHTSA, IIHS only tests a selection of cars annually, typically best-selling models or models that have received a major redesign.

    NHTSA ratings explained

    NHSTA safety testing is conducted at several independent testing facilities across the United States. After evaluating each of the tests below, they assign the vehicle an overall grade on a five-star scale, where five stars is the best rating. Here’s what they look at:

    Frontal crash test

    In order to simulate a head-on crash, a car is crashed into a fixed barrier at 35 mph. Two crash-test dummies of different adult body sizes are placed in the front seats with seatbelts securely fastened. Data collected by the dummies allows researchers to determine potential head, chest, abdomen and pelvis injuries human passengers might suffer under similar conditions.

    Side pole crash test

    In order to simulate a sliding side-crash into an object such as a utility pole, a car is crashed on the driver’s side at 20 mph into a pole with a 9.5-inch diameter. A single, small-sized adult test dummy is used to evaluate potential head, chest, lower spine, abdomen and pelvis injuries that could occur to a driver in this situation.

    Side barrier crash test

    Simulating a side impact from another vehicle, this test has a 3,015-pound barrier moving at 38.5 mph crash into the driver’s side of a parked vehicle. Two crash-test dummies of different adult body sizes are placed in the driver’s seat and the rear driver’s-side passenger seat (i.e., the impact-facing seats). Data collected from the test dummies is used to evaluate head, chest, abdomen and pelvis injuries humans might sustain in the same scenario.

    Rollover resistance test

    The rollover test isn’t an actual crash test and is measured in a lab instead. It uses a formula known as the Static Stability Factor to determine the vehicle’s likelihood of rolling over, based on its center of gravity.

    IIHS ratings explained

    IIHS safety testing is conducted at their research facility in Virginia. Vehicles are put through six different tests and receive a rating of Good, Acceptable, Marginal or Poor. Vehicles that get a rating of Good across all six tests receive the additional distinction of being named an IIHS Top Safety Pick+. Here’s what the IIHS tests:

    Driver-side small-overlap front

    This test simulates a head-on collision in which the impact is primarily on the driver’s side. A car is crashed into a barrier at 40 mph, with two test dummies in the front seats.

    Passenger-side small-overlap front

    This test simulates the same style of collision as above, but with the impact primarily on the passenger’s side.

    Moderate-overlap front

    This test also simulates a frontal collision, but at a different angle. A car is crashed into a barrier at 40 mph, exposing a larger percentage of the vehicle’s front side to impact but still leaning toward the driver’s side. This test requires only a single dummy in the driver’s seat.

    Side impact

    This test simulates a side impact collision. A 4,200-pound barrier moving at 37 mph (often resembling an SUV) is crashed into the driver’s side as the car stays still. Dummies are placed in the impact-facing front and rear seats of the car.

    Roof strength

    This test pneumatically pushes down a metal plate onto the car's roof, depressing it by exactly five inches. The greater the amount of force required to reach that benchmark, the more likely it is the car would perform well in a rollover. In order to receive a Good rating, the car must withstand a force that’s at least four times the car’s own weight.

    Head restraints and seats

    This test simulates a rear-end collision where a static vehicle is hit from behind at 20 mph. This test uses a special, particularly sensitive dummy that mimics the articulation of the human spine and neck.

    In summary

    When evaluating a car for purchase, it can help to pay attention to the car safety ratings by both the NHTSA and the IIHS. While IIHS's testing is slightly more comprehensive, they encourage consumers to look for vehicles that receive a good car safety rating from both organizations, since each one tests different factors that play into a car’s safety. A car with a top vehicle safety rating can’t always guarantee you’ll come out of accidents unscathed, but it can raise your odds of avoiding serious injury. When it comes to the safety of you and your loved ones, that may just be enough to make a difference.

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