Earlier this week, trumpets were blown for Tesla Motors [NSDQ:TSLA], whose Model S luxury electric sedan attained the highest-ever rating in the National Highway Traffic Safety Adminstration's crash tests.

It's an impressive achievement, particularly for such a young automaker. And while the feds weren't so keen on Tesla's revelation that it actually got a 5.4 out of 5 overall score, there's no doubting the Model S is a safe car.

But safest car ever? That's less clear, and for one important reason, notes the Los Angeles Times: Its closest rivals haven't actually been tested.

Not so long ago, we learned that Tesla's Model S sales are actually fairly healthy for its class. On price, it lines up beside cars like the Audi A8, BMW 7-Series, Lexus LS and Mercedes-Benz S-Class, and outsold them all in the first quarter 2013.

However, none of the above have actually been tested by the NHTSA, nor the Insurance Institute for Highway Safety (IIHS). Crashing half a dozen new cars in the name of science is actually quite an expensive pursuit, seriously so when the cars in question are approaching the $100,000 mark.

For that reason, says the Times, the NHTSA tests the models "that best represent what is actually being purchased in the marketplace". Overall, around 85 percent of new cars are tested, typically the models selling in the greatest numbers.

That doesn't tend to include luxury cars selling little more than 10,000 units a year--nor other conspicuously absent vehicles like Ferraris, Bentleys and Lamborghinis. The largest passenger cars currently tested are vehicles like the Mercedes-Benz E-Class and Audi A6, from the segment below.

Tesla slipped through that net thanks to its electric drivetrain, making it worthy of testing for the "new technology factor". But it does make a like-for-like comparison very difficult to achieve. Without carmakers like Mercedes-Benz and BMW paying to have their S-Class and 7 Series put through the tests--something they've no need to do, knowing the cars are well-equipped to deal with accidents--it's impossible to know whether the Model S genuinely is the safest car on the roads.

As the Times points out, you'd struggle to crash one of the latest luxury cars in the first place--the S Class is equipped with pre-warning and pre-collision systems galore, including systems that can apply the brakes if the car decides the driver has left it too late.

The Model S still remains the safest car the NHTSA has tested. It may well be the safest car on the roads. But unless its closest competitors are also crunched for our viewing, we'll not know for sure.


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