A new set of crash tests by the Insurance Institute for Highway Safety questions Tesla's claim that the Model S is the safest car in history. In fact, the person who oversaw the Model S crash tests tells CNBC, "If you're looking for top-line safety, we believe there are other, better choices than the Model S." Dave Zuby, IIHS executive vice president and chief research officer, made that assessment while discussing the results of a new round of crash tests focused on six large cars, including the Model S.

The dummy's position in relation to the door frame, steering wheel, and instrument panel after the second crash test indicates that the driver's survival space was maintained reasonably well overall. Source: IIHS

In one test, the small overlap front collision, the front driver's side corner slams into a barrier at 40 mph. According to the Insurance Institute, the head of the crash test dummy in the Model S slammed into the steering wheel, which is why IIHS only gave the popular electric car an "acceptable" rating in the small overlap test. "Acceptable" is one notch below "Good," the best rating possible by the IIHS. The nonprofit says the driver's side seat belt did not have enough tension to protect the crash test dummy's head. Furthermore, after Tesla said it corrected the problem, the Insurance Institute did the small overlap crash test a second time and came up with a similar result. "We're not saying the Model S is unsafe," Zuby said. "But, the fact we got the same result the second time doing the test was disappointing." Tesla defends the Model S and its safety record.

Pre-crash studio shot Source: IIHS

In a statement to CNBC, a Tesla rep said: "Tesla's Model S received the highest rating in IIHS's crash testing in every category except for one, the small overlap front crash test, where it received the second highest rating available. While IIHS and dozens of other private industry groups around the world have methods and motivations that suit their own subjective purposes, the most objective and accurate independent testing of vehicle safety is currently done by the U.S. government, which found Model S and Model X to be the two cars with the lowest probability of injury of any cars that it has ever tested, making them the safest cars in history." It's true the National Highway Traffic Safety Administration has given both the Model S and the Model X five-star safety ratings, the highest score possible. In fact, the Model X is the only SUV to ever earn a five-star rating from the federal government.

Action shot taken during the second of two small overlap frontal crash tests. Source: IIHS

So, why the difference between the two crash tests? NHTSA's evaluation does not include small overlap front-end collisions, which the IIHS blames for about a quarter of the injuries and fatalities in front-end crashes. "We would argue, that to be considered the safest vehicle on the road, it should earn a 'Good' rating from the IIHS as well as a five-star safety rating from NHTSA," Zuby said. Of the six large cars to be tested by IIHS, three received the designation of being "Top Safety Picks." Those models include the Lincoln Continental, Mercedes-Benz E-Class and Toyota Avalon. Questions? Comments? .

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