When Car and Driver tested the world's top four semi-autonomous cars to see which one had the best hands-free driving, one vehicle stood out the most by a long shot -- and it's made by the newest automaker around: electric-car maker Tesla Motors (TSLA -2.84%).

Tesla's Model S was the "clear winner," wrote Car and Driver's Don Sherman.

Tesla Model S Autopilot. Image source: Tesla Motors.

The test
How did the testing go down?

Car and Driver tested Nissan's 2015 Infiniti Q50S, Daimler's 2015 Mercedes-Benz S65 AMG, BMW's 2016 750i xDrive, and Tesla's 2015 Model S P85D -- the four luxury cars Car and Driver believes "have done the most to purge human frailties from the acts of cruising, braking, and steering."

"Our main focus," the article continued, "was automatic lane keeping: how well these four early semi-autonomous cars guide you safely and securely while relying on their electronic wits instead of the driver's hands, eyes, and judgment."

The route was a 50-mile stretch of Michigan roads including 30 miles of freeway driving, and the other 20 miles were allotted to rural and city driving. Michigan roads in particular "present a daunting challenge to hands-free driving because of their abysmal repair standards," Car and Driver explained.

While the adaptive cruise control for these vehicles is built to work with the freeway, this particular stretch was a challenge.

"Thirty miles of freeway revealed how these vehicles dealt with traffic and lane markings ranging from nonexistent to perfect," Car and Driver said.

To score and compare the vehicles, Car and Driver tallied the number of interruptions caused by "broken lane marks, inconsistent pavement patches, intersections, and exit and entrance ramps."

The winner
Tesla's Model S was the stand-out winner among the four vehicles tested. And the magazine had plenty of praise for the vehicle's Autopilot system:

The Tesla's Autosteer performance can be distinguished from our other contenders by two words: no wobbling. This car identifies the exact center of your lane of travel and holds that course with minimal deviation. This system rises well above parlor-trick status to beg your use in daily driving.

Also to Tesla's credit, this is the only car capable of hands-free lane changes. You simply use the turn signal the normal way and the Model S glides smoothly into the next lane after verifying that there's space to do so safely.

Car and Driver concluded that Tesla's Model S Autopilot technology "lives in a class of one."

Model S Autopilot. Image source: Tesla Motors.

Tesla's autopilot technology experienced 29 interruptions on the challenging route, compared with BMW, Mercedes, and Infiniti at 56, 58, and 93, respectively.

Tesla's rise to lead the automotive industry in semi-autonomous technology has been rapid and sudden. Just four months ago, Tesla's Model S wouldn't even have qualified to compete in this test. It wasn't until October that the automaker beamed automatic steering, lane changing, and parking abilities to its fleet via an over-the-air software update. 

Going forward, Tesla plans to move aggressively with more improvements to its vehicles semi-autonomous features, with an aim to eventually reach general autonomy. The company said in a recent blog post that Tesla's vision is to dramatically improve safety as it converges its new autonomous Summon feature, which enables a Tesla vehicle to park and unpark itself without a driver, and its semi-autonomous autopilot technology.