MOUNTAIN VIEW — After a year of testing its bubble-shaped driverless cars on the empty roads of a shuttered Central Valley military base, Google is about to deploy its fleet on the busy streets of Silicon Valley.

For now, the cars must have safety drivers ready to grab the wheel or hit the brakes if something goes wrong. But self-driving software could soon move from test cars to consumer vehicles as the California Department of Motor Vehicles puts finishing touches this month on new operational rules for autonomous cars, making it the first government in the world to create a detailed handbook for robots on the road.

“Our goal is to create something safer than human drivers,” said Google co-founder Sergey Brin, speaking this week as his company’s two-seater prototype zoomed around a rooftop parking lot in Mountain View. “And keep improving from there.”

Citing his engineering team’s major advancements in the past six months in understanding a bicyclist’s hand signals and other real-world scenarios, Brin stood by his prediction that the technology is “still roughly on track” for consumers boarding fully autonomous cars by 2017. But a scholar advising the DMV on its new rules believes a car that can safely navigate by itself through crowded San Francisco streets is still “many decades” away.

“There’s not going to be some sudden burst of new things that pop onto the market as soon as the new regulations are out there,” said Steve Shladover of UC Berkeley’s Institute of Transportation Studies. “The progress will be quite gradual and incremental.”

Unlike Google, most of the companies with permits to test self-driving cars in California — including Mercedes-Benz, Delphi Labs, Tesla and Audi — are aiming to advance and sell products that assist human drivers rather than fully take over.

The competing predictions, and varying degrees of robot control, leave regulators with the challenge of balancing the rules that are needed now — as the technology still has unforeseen hiccups — with a future when fully autonomous vehicles become more common.

“This is our very first time we’ve had to do something like this, and not many states are in our situation,” said Bernard Soriano, the DMV deputy director in charge of drafting the new rules. “There are a lot of eyes on what we’re doing.”

The draft rules — due several months ago — will be released soon, Soriano said, and will be followed by a public hearing this summer. Nevada, Michigan and Florida also have established rules, but mostly for testing and none as detailed as what California is preparing.

Seven companies have had permission since September to test-drive autonomous vehicles in the state. Even before those rules were in place, Google had spent years test-driving Lexus SUVs outfitted with self-driving software.

But “in the next month or so,” Google will be launching its own 25 prototype cars onto Mountain View public roads for test drives. They will be restricted to neighborhood roads, with speeds capped at 25 miles per hour.

The public experiment is designed to see how the cars interact with people, said Chris Urmson, who reports to Brin as the head of Google’s self-driving car project.

Those cars have already spent a year navigating over potholes and through obstacle courses at the former Castle Air Force Base near Merced, but this will be the first time they will have to respond to pedestrians who aren’t Google employees. Their movements through Mountain View will be based not only on the car’s radars, lasers and cameras, but also on a kind of memory — the car’s software already contains a meticulously detailed map of the city’s suburban streets.

On Wednesday, Urmson’s team showcased the cars to a small group of reporters, along with Mountain View residents and people who are blind or disabled and are eager for the day when a self-driving car can get them around.

To make its vehicles safe, Google has made them conservative. That means, for instance, that they are programmed to wait for a second and a half before moving through a green light.

The caution can also make them jittery, causing the cars to brake for perceived dangers that a human driver would know to be harmless. A mingling crowd of onlookers on the roof of Google’s garage was calculated to be a threat Wednesday, though to a human eye none showed signs of darting out.

That also raises another concern: What if the cute car’s cautious demeanor grates on impatient commuters in a hurry to get to their Silicon Valley jobs?

“We’ve been honked at a few times,” Urmson said, speaking of the Lexus SUVs that have been riding through the area for years. “We’ve had people gesticulate, but overall it’s been incredibly positive. We’d had more thumbs up than fingers up.”

Google engineers are also pleased with the car’s caution. Believing that self-driving cars will make roads safer and less congested, Urmson disagreed with Shladavor’s prediction that the technology is still decades away.

“I’m an optimist, and it’s just too important,” Urmson said. “There are 90 people every day dying on America’s roads. We should be impatient about this technology.”

Contact Matt O’Brien at 408-920-5011. Follow him at Twitter.com/mattoyeah.