SONOMA, Calif. — Markus Hoffmann, an engineer at Audi, prepared himself for a high-speed run around the Sonoma Raceway here in Northern California.

But instead of grabbing the steering wheel, he clutched a button he would release only if something went awry. The car, which he called Robby, was going to negotiate the two-and-a-half-mile Nascar track by itself — at 120 miles an hour.

“If something goes wrong, I’ll take over,” he said, giving a thumbs-up to engineers in the stands.

With that, a computer in the trunk twitched the steering wheel into position, and Robby took off. “I’m doing nothing except holding the kill switch down,” Mr. Hoffmann told his passenger, somewhat reassuringly.

As the Audi RS7 negotiated hairpin turns on the road course at top speed and came within inches of the raceway’s walls, it became clear after some tense moments: This car knew what it was doing.