Vehicle Safety: The Reasons Behind the Ratings

When buying a car, there are typically three top criteria that people look at: make and model, price, and safety. Other factors—the interior, the top speed, how much trunk space is available—may migrate towards the top of the “priority” list, but when it comes down to it, the old saying is “safety first” for a reason.

Within the United States, there are two agencies that conduct crash tests and various other tests to rate the safety of most cars on the market, the NHTSA (the government organization) and the IIHS (a private, nonprofit organization funded by insurance companies and agencies). The National Highway Traffic Safety Association and the Insurance Institute for Highway Safety both work together to offer a well-rounded projection of the safety of the car by conducting different tests that pair together. aims to provide an overview of the overall safety of the car by taking both scores into consideration.

In 2011, the NHTSA improved the 5-star rating system that was established under the New Car Assessment Program (NCAP) in the year 1978. Tests performed by the NHTSA include frontal impact crash tests, side impact crash tests, rollover assessments, and side pole crash testing ( Each test enacts a different scenario involving speeds of around 35 mph and with cars of a similar size. Cars rated by the NHTSA before 2011 aren’t comparable to the ratings of cars rated after 2011 because of the new, more stringent crash tests, and ratings can’t be assumed to be applicable in crashes involving cars of two different sizes. However, their rating system of 1 to 5 stars, with more stars meaning safer cars, gives car owners a good sense of their safety while driving. readers should know that cars that earn 5 stars in all four tests across the board become part of the 1% of cars to do so. To provide even more accurate data, crash test dummies of different sizes and shapes are also now being used in crash tests (

To complement the tests completed by the NHTSA, the IIHS rates vehicles good, acceptable, marginal, and poor based “on performance in five tests: moderate overlap front, small overlap front, side, roof strength and head restraints” ( For a car to earn the Top Safety Pick or Top Safety Pick+, scores of “good” must be earned in the majority of tests, and “acceptable” ratings must be earned in the other categories. The IIHS tests focus on crashes on one side of the front end of the car, instead of full frontal, because of the belief that most drivers will try and turn to avoid an accident. They also use a side-crash barrier that is similar in size to an SUV or truck, versus the sedan-sized barrier the government (NHTSA) uses in its tests, and smaller dummies to provide an even broader range of data to compile with the NHTSA. The IIHS tests also use slightly higher speeds and heavier barriers in their tests.

Even with the extensive vehicle coverage between the two agencies, not all cars hitting the market are tested. Due to restrictions in budget and time, most volume cars (cars projected to sell well across the nation) are tested, although the IIHS claims it “makes a point to test such innovative cars as the all-electric Nissan Leaf and the plug-in hybrid Chevrolet Volt” ( According to Consumer Reports, about 80%-90% of cars were tested for the 2012 model year.
While not all cars are tested, and the ratings themselves have a few flaws (for instance, not being upheld in crashes between different sized cars or for drivers of different heights and weights other than average), the two agencies are working towards even more innovative and accurate tests and technology to reduce crashes overall. More stringent tests will provide visitors with more definite and reliable data and safety ratings in the upcoming years, leading to easier research, more confident car purchases, and, most importantly, a safer experience on the road, both to the driver and those around them.

Vehicle Safety Rating Guide