MOUNTAIN VIEW, Calif.

THE “look Ma, no hands” moment came at about 60 miles an hour on Highway 101.

Brian Torcellini, Google’s driving program manager, had driven the white Lexus RX 450h out of the parking lot at one of the company’s research buildings and along local streets to the freeway, a main artery through Silicon Valley. But shortly after clearing the on-ramp and accelerating to the pace of traffic, he pushed a yellow button on the modified console between the front seats. A loud electronic chime came from the car’s speakers, followed by a synthesized female voice.

“Autodriving,” it announced breathlessly.

Mr. Torcellini took his hands off the steering wheel, lifted his foot from the accelerator, and the Lexus hybrid drove itself, following the curves of the freeway, speeding up to get out of another car’s blind spot, moving over slightly to stay well clear of a truck in the next lane, slowing when a car cut in front.

“We adjusted our speed to give him a little room,” said Anthony Levandowski, one of the lead engineers for Google’s self-driving-car project, who was monitoring the system on a laptop from the passenger seat. “Just like a person would.”

Since the project was first widely publicized more than two years ago, Google has been seen as being at the forefront of efforts to free humans from situations when driving is drudgery. In all, the company’s driverless cars — earlier-generation Toyota Priuses and the newer Lexuses, recognizable by their spinning, roof-mounted laser range finders — have logged about 300,000 miles on all kinds of roads. (Mr. Torcellini unofficially leads the pack, with roughly 30,000 miles behind the wheel — but not turning it.)