Several years ago, I tested Cadillac Super Cruise and Tesla Autopilot, more or less back-to-back.

Both Cadillac and Tesla have continued to improve their respective semi-self-driving systems, since then.

Tesla has added features to Autopilot, while Cadillac has upgraded Super Cruise and broadened the number of vehicles it's available on; General Motors is also bring Super Cruise to the Chevy Bolt family of electric vehicles.

Cadillac Super Cruise is the better of the two systems, but it's focused on highway driving, while Tesla Autopilot is more versatile.

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The two best semi-self-diving features in the car market are still Tesla Autopilot and Cadillac Super Cruise.

Tesla's system has been around longer (it debuted in 2015) and uses cameras, radars, sonar, and GPS navigation. In particular, the camera-based visual technology demands that each vehicle with the latest Tesla hardware also contains supercomputer-level processing power, so that it can crunch all the data.

Cadillac's Super Cruise, which arrived in late 2017, also uses cameras, notably a small unit mounted on the steering column that monitors whether the driver is paying adequate attention. The cameras that manage actually driving the car are aimed at the road and surroundings, however, and are matched with a radar system. But critically, Cadillac also makes use of hundreds of thousands of miles of laser-radar (Lidar) maps, and as long they're current, the vehicle can determine exactly where it is.

Both systems are essentially adaptive-cruise control — which calibrates distances between cars and adjusts throttle and braking accordingly — plus automatic steering. They're far from the dream of affordable full autonomy. (Although Cadillac parent General Motors has in Cruise, a company it acquired in 2016, a fully self-driving business on the horizon; and Tesla is aggressively pursuing what it calls "full self-driving.")

I was lucky in that I got to try them both out. I sampled Super Cruise in a Cadillac CT6 sedan on a drive from New York City to Washington, DC and Tesla's Autopilot in a Model X on a jaunt from New Jersey to rural Maryland. (The Caddy drive was a manufacturer event, while the Tesla trip was the result of Tesla letting me borrow a vehicle for a few days.)

Which performed better? Read on.