Tesla Motors doesn't like to brag. Okay, yes, it does. The electric-car maker announced this week that its Model S sports sedan was awarded the highest safety rating the National Highway Safety Administration had ever bestowed on a vehicle.

"Of all vehicles tested, including every major make and model approved for sale in the United States, the Model S set a new record for the lowest likelihood of injury to occupants," the company boasted, with a bravado that is typical of CEO Elon Musk.

The Model S scored a 5.4 on the agency's 5-star scale, getting perfect marks in every category and out-performing the NHTSA's highest standards in others. What made this electric car so safe?

One reason: It's an electric car, which means that it has a battery-powered engine up front that is not as big as a conventional engine filled with combustible fuel. That gives it a larger crumple zone to absorb a high-speed, head-on impact.

It also has a heavy battery pack mounted beneath the floor, giving it a low center of gravity that made the car impossible to roll over using the standard testing methods. The test team had to figure out a way to tip it over. That same stability also gave the test vehicle exceptional handling, a safety plus in treacherous driving conditions.

Green-energy fans couldn't contain their glee. And auto experts confessed they were awestruck.

Ashlee Vance at Bloomberg Businessweek noted that when the safety regulators tried to test the vehicle's roof strength by crushing it, "the crusher was crushed." The testing machine failed after exerting pressure equal to piling four other Model S's on the vehicle's roof; indeed, the testers still don't know how many cars you could put on top of the Model S before it caves in. "So, Model S owners, you can sleep easy if a Carnado ever rolls through town," Vance said.

There's one hitch. "This is welcome news for what's proving to be the most successful electric vehicle on the market," said Annie-Rose Strasser at Think Progress. "But not everyone will be able to benefit from the resounding success of the Tesla. At a price tag of $60,000 to 90,000 per vehicle, the safety that comes from a Model S is far out of reach for the majority of consumers."