When Ohioan Joshua Brown took his Tesla Model S for a spin earlier this month, he got familiar fast with how handy the autopilot system could be — as it took over and avoided a crash.

In comments attributed to the driver alongside the video, posted earlier this month on YouTube, he recounted what happened when a heavy truck equipped with a hydraulic lifting system, unbeknownst to him, nearly sideswiped him:

“I was driving down the interstate and you can see the boom lift truck in question on the left side of the screen on a joining interstate road. Once the roads merged, the truck tried to get to the exit ramp on the right and never saw my Tesla. I actually wasn’t watching that direction and Tessy (the name of my car) was on duty with autopilot engaged. I became aware of the danger when Tessy alerted me with the ‘immediately take over’ warning chime and the car swerving to the right to avoid the side collision.”

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Brown said he has done lots of testing with “Tessy’s” sensors and software capabilities but “had not tested the car’s side collision avoidance.” He’s had the car since July 2015 and says he’s logged about 39,000 miles so far.

Last summer, Tesla TSLA, +4.42% Chief Executive Officer Elon Musk said the company was nearly ready to have its cars operate driverless on highways and to do some self-parallel parking. The Model S cars have built-in driver-assistance systems that include, among other things, forward radar, a camera mounted by the rear-view mirror, and 12 sensors that can sense objects within 16 feet of the car.

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Not everyone is comfortable with Tesla’s autopilot feature. CarBuzz posted a video of a 70-year-old grandmother sitting behind the wheel and basically wringing her hands, saying, “Oh my,” and anxiously exclaiming: “Oh, there’s cars coming. ... Oh, where’s it going?”

Here’s that video, also posted on YouTube: