SAN RAMON, Calif. — Electronic chimes sounded as the self-driving minibus halted its crawl through the parking lot of an upscale office park here. There was no obvious reason for the stop, so its operator made a note to report it, then used a touch screen to restart the shuttle’s test drive.

The bright red, 12-passenger vehicle, which maxes out at 12 mph and was designed by French firm EasyMile, is part of an effort to use autonomous technology to improve access to transit stations in the area. But first, as the unscheduled stop on a breezy April day showed, the shuttle needs extensive testing to make sure it’s safe for public roads.

California regulations allow testing of self-driving vehicles, even as a lack of federal rules prohibit commercial sales or interstate travel. That means the EasyMile vehicle can legally operate on public streets in a limited capacity.

California in 2012 became one of the first states to enact rules of the road for vehicles using various levels of automation, spurred by what was then Google’s self-driving project — now Waymo, a separate unit of the Alphabet parent corporation — and other home-state developers.

A 2016 state law allows the testing at Bishop Ranch, a 100-acre office park about 20 miles east of San Francisco. There are 30,000 workers here, including employees of General Electric, AT&T, Chevron and Toyota.

The federal Transportation Department and the National Highway Traffic Safety Administration have so far offered only guidance and requested autonomous vehicle developers to submit voluntary safety self-assessments. And despite high-profile bills in both chambers during the 115th Congress (2017-18), federal lawmakers have yet to enact an autonomous vehicle law, leaving states as the primary forces shaping policy.

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Randy Iwasaki, executive director of the county transportation authority, said that in the absence of federal standards, the county’s program could address problems of safety, climate change and congestion.

But success is far from a sure thing. The 12 miles-per-hour limit restricts usability, and the vehicle’s artificial intelligence has room for improvement, Iwasaki said.

Though it only follows a preprogrammed route — a roughly five-minute loop around the parking lot of Bishop Ranch — items as common as overgrown foliage can disrupt the ride.

After testing for months in the Bishop Ranch parking lot, CCTA tested the autonomous bus going through an adjacent intersection with a traffic light. While the parking lot is relatively flat, the intersection was on an incline, presenting a complication that required developers back in France to adjust the program.

Such hiccups generally result from an abundance of caution. Minutes before the unplanned stop in the Bishop Ranch lot, the vehicle had made a similar stop to avoid hitting a CCTA employee who purposely jaywalked in front of the vehicle to demonstrate the vehicle’s capacity to detect and avoid pedestrians.

But imperfections contribute to a sense that the government needs to control how and when the technology is used, as advocates face a challenge in turning public perception in its favor. Polling has consistently shown Americans are skeptical about autonomous vehicles, including a 2018 Gallup survey in which 52 percent of respondents said they’d never want to use a self-driving car even if certified as safe by government regulators.

Phil Ting, a Democratic member of the State Assembly from San Francisco who’s written laws related to autonomous vehicles, said he’s a big supporter of the technology, but doesn’t want it to be rushed to the public in a way that would jeopardize safety.

“There’s no question, long-term, that this technology is here to stay. It’s just a matter of when, not a matter of if,” he said in an interview off the Assembly floor in Sacramento. “We obviously don’t want the technology to be deployed before it’s 100 percent.”

Twenty-nine states now have laws regulating self-driving vehicles on the books, with a variety of approaches, according to the National Conference of State Legislatures.

As on many issues, California’s regulations are more robust than those in other states. Developers must turn in reports for every test on a public road that results in unexpected disengagements. The unexplained stop by the EasyMile bus, for example, would have required a report if it occurred outside the test lot. Regulatory authority is split between the DMV for general licensing for testing and the Public Utilities Commission, which oversees taxis.

Some companies have expanded testing to states with more lax regulations like Arizona or Florida. Waymo operates a limited autonomous taxi service in the Phoenix area, which it expanded last month to more members of the public.

Still, 62 companies with licenses to test autonomous vehicles remain in California, due in large part to the base of engineering talent in Silicon Valley and the potential for a consumer market.

Ting said states should be allowed to add their own regulations on top of a federal baseline, but “a lot is lost” by not having federal standards to provide regulatory certainty across the country.

“It’d be great for the feds to have one set of rules that we can all operate under and there really is a set of laws that everyone’s following across 50 states,” he said.

Bert Kaufman, the head of corporate and regulatory affairs at Zoox, said the nonbinding guidance from the federal government has been encouraging. Still, as countries like Japan and Singapore move forward with testing, it’s important for U.S. leaders to show they value the technology as well.

“Federal legislation is important because it sends a signal to the rest of the world about how seriously we take this very worthy pursuit of leading the way in autonomous mobility,” Kaufman said.

But state-level policymakers were among those who sank bills in Congress last year, concerned the language gave too much power to federal authorities and that it limited state power to regulate the technology.

Eventually, federal standards will be needed to allow vehicles to cross state lines. For now, though, Florida state Sen. Jeff Brandes said there’s no problem letting different states take different approaches without interference from the federal government. A federal law isn’t yet needed, according to Brandes.

Autonomous vehicle technology promises to upend decades of transportation practices, and save lives, time and fuel, say advocates. But that will require winning over a skeptical public and establishing regulations large and small.

In addition to major challenges, like updating standards for vehicles that no longer require a steering wheel or human driver, there are smaller issues to address.

In California, Ting wrote two bills enacted last year that clarify police officers’ authority over autonomous vehicles and authorize San Francisco to levy a tax on what companies will eventually charge for rides.

Another bill this session, offered by Bill Dodd, a Democrat from Napa, would require a human operator to be present in any autonomous vehicle operated by a public transit agency. Bus drivers are often tasked with helping elderly and disabled riders, and a system that runs autonomously would need to fill that same role, he said.

As lawmakers tackle these issues and others, they’re faced with the reality that the pace of the technology’s development makes it difficult to know exactly what they’re trying to regulate.

Asked what the next step for regulation would be, Ting said he wants to wait and see.

“I think we’re just going to be watching to see how the technology develops,” he said.