Tesla crash test: Does record safety rating mean electric cars are safer?

[Editor's note: Paragraph eight below has been updated to clarify Russ Rader's comments. The added weight of batteries are an advantage for electric cars in real-world accidents, not in crash tests, as was previously implied.] 

Tesla Motors Model S is among the safest cars ever tested by the National Highway Traffic Safety Administration. 

The luxury electric sedan earned an overall safety rating of five out of five stars from the federal agency, Tesla announced Tuesday. It also earned at least five stars in every category, a feat that puts it in the top 1 percent of cars tested by NHTSA.  

The Tesla crash test is yet another win for a company that cannot seem to lose lately. Tesla Motors' Model S continues to earn glowing reviews, bolstering its stock price, and drawing the envy of an incumbent auto industry that might rather see it fail. Its stock price was up 2 percent to $148.39 in midday trading.

The design flexibility afforded by an electric vehicle may be a key to the Model S's record safety rating, challenging early public perceptions of electric cars as weak vehicles, prone to battery fires and other mechanical failures. 

Because the $70,000-plus electric car does not require a large gasoline engine block, there is added room in the front of the car for crumple zones, which absorb energy from front-end collisions. The motor is only about a foot in diameter and is mounted close to the rear axle, away from the most common impact zones. The car's front section is instead used as a second trunk.

"A longer crumple zone means there’s a longer period of time in which the crash is unfolding," said Russ Rader, a spokesman for the Insurance Institute for Highway Safety, which has not yet tested the Model S. "The vehicle can slow down over a longer period of time, which benefits the people inside."

In its press release, Tesla compares it to a diver jumping into a pool of water from a tall height. "[I]t is better to have the pool be deep and not contain rocks."

Other electric cars have performed well in safety tests, Mr. Rader noted in a telephone interview, and the added weight of lithium-ion batteries can give cars like the Chevy Volt and Nissan Leaf an advantage in real-world crashes.

"It's simple laws of physics," he said. "If you’re in a crash between a heavier vehicle and a lighter one, the heavier vehicle will perform better than a lighter one."

Failures of those energy-dense, advanced batteries have heaped scrutiny onto the electric car industry. In January 2012, General Motors recalled 8,000 Chevy Volts after a federal probe into three fires in Volt battery packs after crash tests. But Tesla reported that its Model S battery passed the NHTSA test with no serious issues, and emphasized the lack of any reported battery fires in its production vehicles' histories.

It made another claim that is likely unique in an industry that results in about 34,000 fatalities in the US each year: "While this is statistically unlikely to remain the case long term, Tesla is unaware of any Model S or Roadster occupant fatalities in any car ever."

Tesla has delivered more than 15,000 electric vehicles in its 10 years of existence.