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.
Auto engineers at traditional carmakers like Audi, and at Google and Tesla, are in an arms race of sorts in the rush to build self-driving cars, a technology, they say, that will make driving safer and free drivers of mind-numbing hours behind the wheel.
But to do that, they first must clear an important hurdle: winning the public’s trust to let go of the wheel.
Building faith in autonomous technology is pivotal for Audi, which says that in the next three years it will sell a luxury sedan that can control itself in a traffic jam — a driving experience that fries the nerves of human drivers but doesn’t faze computers.
Cadillac is also planning to introduce a self-driving feature, Super Cruise control, for highways in a coming model. And Elon Musk, founder of Tesla, has promised a software update this summer to existing Model S cars that will allow them to steer themselves on limited-access roads.
But is the public ready?
One way Audi plans to inspire confidence in consumers is by taking design cues from commercial airplanes, which people already trust, even when they know that a computerized autopilot is guiding them through the air.
A coming Audi A8 will be loaded with redundancies — two braking systems, two steering systems — so that if one fails, the computers can use the other to operate the vehicle. The concept is inspired by planes, which often fly with three versions of their most crucial components.
Another pair of redundant systems is, essentially, the car’s eyes. A front- and rear-facing camera system, along with a highly precise GPS, can tell Audi prototypes where they are on the track, which the computer has memorized. If the positions the systems give don’t match, the automation shuts down.
Audi’s cars are far from being completely autonomous, Audi engineers say. They are “piloted” by the driver, language borrowed from aviation that is meant to imply that the person sitting in the driver’s seat is still ultimately in control.
But Bryan Reimer, a research scientist at the Massachusetts Institute of Technology, warned that the analogy to pilots went only so far.
“It’s a myth that the more automation you have, the less education you need,” he said. “The pilots are there to supervise the automation and take control when the automation exceeds its boundaries.”
The A8 will be able to drive itself only at low speeds on highways when traffic is tight, reassuring the driver it can see what is ahead by displaying road signs it spots on the navigation screen. And that leads to a second challenge for engineers: how to tell drivers cruising on autopilot when they need to take control.
Audi’s engineers have created visual and tactile cues that the car is taking over: The steering wheel retracts, and lights lining the top of the dashboard glow green. When the driver needs to take control again — at a highway exit, for example, or as traffic clears — the lights blink red, a repeating tone comes from the speakers, and the wheel juts back into the driver’s lap.
The signals are meant to be unambiguous: Take back the wheel, now.
But given the novelty of autonomous features, which combination of signals is best for getting drivers’ attention remains unclear.
Anuj K. Pradhan, a scientist at the University of Michigan’s Transportation Research Institute, said that research in the field was in its infancy, including the work being done at his lab.
“We have fewer answers than we have questions,” he said.
Consider all the variables: What if the driver is reading a book? Or is hard of hearing? Or dozes off?
“Let’s be honest,” said Brian Lathrop, a cognitive psychologist who works on autonomous technology for Volkswagen brands, including Audi. “People will likely fall asleep.”
For that, Audi has an in-car alarm clock: The repeating tone grows louder until the driver wakes. It will also have a facial recognition system that can tell if the driver is asleep.
“At this point, substantial effort in the automotive community is focused on developing fully autonomous driving technology,” said Karl Iagnemma, an automotive researcher at M.I.T. “Far less effort is focused on developing methods to allow a driver to intuitively and safely interact with the highly automated driving vehicle.”
In any case, the autonomous future has not come at once, which only highlights the need to ease consumers into the idea that cars will be able to change lanes on their own.
In contrast, Google has focused on developing a completely autonomous car. The company says that the evidence points to just how reliable self-driving cars will be, provided they win the trust of drivers.
In June, Google released information on all accidents the cars were involved in. Over six years of testing, there were 12 accidents. None of them were caused by the self-driving cars, the company said.
“If there is one accident, it will hurt the whole field,” said Ewald Goessmann, executive director of the Electronic Research Laboratory, a Volkswagen research facility in Silicon Valley.
Back at the Sonoma Raceway, Mr. Goessmann and other Volkswagen employees entertained rotating groups of lawmakers and Silicon Valley executives by letting them drive a RS7 around the track.
Rodney Ellis, a state senator from Texas, looked slightly nervous before his ride in Robby, but was impressed afterward. “It was a lot smoother than when I did it,” he said.
Bill DeSteph, a member of the Virginia House of Delegates and an auto enthusiast, said the drive was fascinating. “I’m ready to order it now,” he said.
An article on the Automobiles page on Friday about teaching drivers to let autonomous cars take over misspelled the surname of a scientist at the University of Michigan’s Transportation Research Institute and omitted his middle initial. He is Anuj K. Pradhan, not Prahan.