Tesla Model S: Safest Car on the Road
By EV World Editorial Staff
Tesla just keeps rolling with one landmark achievement after another; this time earning the NHTSA's highest crash test rating ever.
Exactly one month ago readers of Tesla Motor's online forum were questioning the safety of the Model S, pointing out that NHTSA had not yet crash rated the car, which at the time was true.
In its defense, Tesla offered photographs of two recent crashes involving their Model S: one a head-on collision with a Honda Accord, the second involving a BMW M-series that had run a stop sign. The visual consequences are pretty horrific… for the people in the other cars. The Tesla drivers both walked away with only minor injuries.
That was then.
Now Tesla has independent, third-party documented proof of the world-class crash safety of their cars. The U.S. National Highway Traffic Safety Administration has awarded the Model S an extremely rare five-star safety rating in all of its crash test categories. Only one percent of all vehicles tested have achieved that distinction. In fact, while NHTSA only publishes ratings of 5, the Model S actually achieved an unprecedented combined 5.4 star rating.
Traditionally, Volvo cars have been considered the safest on the road, but they now have a new challenger for that distinction. In its official press release announcing the results of its crash tests, Tesla points out that in the case of the side pole intrusion test (see video below) - considered the most difficult to pass - it dramatically surpassed the Volvo S60, which preserves 7.8 percent of the driver residual space after its crash test compared to the Model S 63.5 percent.
So, how does Tesla do it? What's different about their design that makes it so much safer than 99 percent of the cars on the road?
For starters, it's an electric car. That means it doesn't have a heavy ICE-age engine mounted in front of the passengers. It's twin electric motors are mounted in the rear axle. Normally, it would be argued that having that engine block up front improves the safety of the car, but in fact, engineers have to design gasoline and diesel engine vehicles so that in a frontal impact the engine block is shoved down and away from the passenger compartment, absorbing some of the kinetic energy, but also reducing the ability to engineer a better crumple zone.
In the Model S's case, the absence of an engine block allowed engineers to improve the crush zone. They explain…
The Model S has the advantage in the front of not having a large gasoline engine block, thus creating a much longer crumple zone to absorb a high speed impact. This is fundamentally a force over distance problem – the longer the crumple zone, the more time there is to slow down occupants at g loads that do not cause injuries.
To handle the side impact and side pole tests, Tesla nested…
multiple deep aluminum extrusions in the side rail of the car that absorb the impact energy (a similar approach was used by the Apollo Lunar Lander) and transfer load to the rest of the vehicle. This causes the pole to be either sheared off or to stop the car before the pole hits an occupant.
For the rear impact test, they created a double rear bumper when the third row child's seat option is installed.
The third row is already the safest location in the car for frontal or side injuries.
While crash testing is a deadly serious exercise, Tesla pointed out, not without a sense of irony, I am sure, that when it came to the rollover test, the independent testing agency couldn't get the car to rollover using its normal procedures.
The reason for such a good outcome is that the battery pack is mounted below the floor pan, providing a very low center of gravity, which simultaneously ensures exceptional handling and safety.
Instead, the contractor had to resort to "special means... to induce the car to roll." And then when testers tried to crush the car's roof, the test machine failed at 4Gs. Translated into layman's terms…
...this means is that at least four additional fully loaded Model S vehicles could be placed on top of an owner's car without the roof caving in. This is achieved primarily through a center (B) pillar reinforcement attached via aerospace grade bolts.
Finally, the lab put the front crash vehicle on the equivalent of barbecue spit and slowly rolled it through 360 degrees (see end of front crash test video below) to see if, like several early crash-tested Chevrolet Volts, they could induce a battery short and cause the car to catch fire. It didn't. In fact, Tesla points out that not a single Model S or Roadster has ever caught fire despite being involved in "several high speed impacts" like those mentioned above. They add…
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.
Telsa acknowledges that "it is possible to game the regulatory testing score to some degree by strengthening a car at the exact positions used by the test machines." They then set about making sure the car could achieve 5 stars "no matter how the test equipment was configured."
The result is a historic 5.4 stars… and recognition as being the safest car on American roads.
Crash Test Videos
Light Pole Impact
Originally published: 21 Aug 2013
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