San Francisco will allow 750 more electric rental scooters onto the streets Sunday as the second phase of a pilot program rolls out.

That brings the total number of scooters allowed in the city to 3,250. It’s a mark of cautious approval for a clean but controversial technology, which still leaves people worried about illegal sidewalk riding and injuries.

Scoot, owned by Santa Monica company Bird, has a permit for 1,000 scooters. Lime, Jump (owned by Uber) and Spin each can offer 750; before Sunday, those three companies were each limited to 500.

Companies said more scooters could be expected in the Mission, Castro, Western Addition, Bayview Hunters Point, Excelsior, Ingleside, and Outer Mission neighborhoods, and in the San Francisco State University area.

Two months into San Francisco’s pilot program, Supervisor Aaron Peskin cautiously voiced support.

“I would say so far, not bad, compared to ‘scooter-geddon’ of last year,” Peskin said, comparing the unregulated scooters that swarmed city streets in spring 2018 to an apocalypse. “Although there is still some sidewalk riding and still some injuries, all in all the rollout has been going well.”

A number of concerns remain, he said, including whether the batteries end up in landfills, equitable distribution of scooters, brain injuries from accidents and sidewalk riding.

Norman Yee, president of the Board of Supervisors, said he wants to see companies take more ownership and responsibility regarding safe use of their products on the streets. Riding on sidewalks is still a problem, and enforcement “is being put on the shoulders of our Police Department, which would cost the city more money,” he said.

Yee recently backed legislation that created the Office of Emerging Technology to regulate new tech inventions, like scooters when they first hit the streets.

Rohit Agarwal, cruising along a downtown alley on a Scoot on Friday, said he uses scooters almost daily because they’re the most efficient way to get from his Potrero Hill home to work at Second and Mission streets.

“They’re hyper-efficient and fun, but the safety is a bit questionable,” the 35-year-old investor said. He’s fallen twice while riding. Once, he was hit by a door opened by a ride-hailing passenger while he was in the bike lane. The second time, he slipped on a pebble. Both times he was just bruised.

Agarwal said scooters are faster than rental bikes but more expensive — an average of $5 to $8 for the scooter, cheaper in the morning than the evening, versus $2 for a bike. When it’s raining, he takes a shared car ride that costs the same as a scooter.

Agarwal, who described himself as an “avid regular user,” said the city is “probably not” ready for more scooters.

“I like it a lot and I find it very convenient and super helpful, but I think it’s inevitable, given how congested the city is, that there will be more accidents,” he said.

Karin Flood, executive director of the Union Square Business Improvement District, said things have gotten better since scooters flooded the city last year, but there’s no ideal place to ride them. Scooters pose dangers and are illegal on San Francisco sidewalks. But “the street does not seem like a safe option right now,” she said.

The San Francisco Municipal Transportation Agency stresses that the safety of riders and pedestrians is its top priority. It requires companies to take measures to educate riders about the sidewalk ban and introduce deterrents, fine or suspend riders who break the rules. California does not require adult riders to wear helmets.

Lime said the agency levies a $100 fine for infractions, which it passes along to the responsible rider with information about how to not repeat the offense. Uber said it’s planning to do the same.

Spin outlines its fee structure: $10 for a first sidewalk riding offense, $25 and a 24-hour suspension the second time, account and payment method banned the third. Improper parking gets warnings that escalates to $5 on the second offense, $10 the third time, and account suspension after that.

Most companies post their riding rules in small type on their scooters, either on the neck or near the handlebars. They also have in-app messaging and community meetings to educate the public.

Scoot said less than 1% of its rides result in a parking complaint and 78% of its riders signed an in-app pledge to follow road rules before using the app. The company said its employees identify poorly parked and ridden scooters and report them to management.

Uber is developing an in-app feature to detect sidewalk riding that it hopes to test in San Francisco soon and is talking with advocacy groups about creating a scooter-like vehicle for people with disabilities. Lime, after organizing meetings with advocates, is on track to launch its adaptive vehicles in January.

Spin said that in high-traffic areas, employees are available near lined-up scooters to explain city rules. It also plans to install more parking hubs to reduce clutter.

George Franklin, 66, a longtime city resident who now lives in Berkeley but works in North Beach, suggested the city spend money on signs warning scooter users that riding on the sidewalk is a violation.

Another longtime resident, Fran Taylor, 70, has submitted a dozen complaints about scooters on sidewalks but said that recently “she’s sort of given up” because nothing seems to change. She said sidewalk riding affects seniors, parents of young children and people with disabilities.

“My main concern was having them come at you on the sidewalk and a lot of the sidewalks are narrow and crowded,” Taylor said. “Sidewalk space historically hasn’t been respected in San Francisco. ... This just seemed like the latest assault.”

Taylor said scooters could be a great alternative to cars if they’re used on the street or in bike lanes.

A May report from Boston Consulting Group found that scooter companies are hard-pressed to make money: The devices have an average life span of three months, but companies need four months to break even per device. Longer-lasting batteries may help.

The report also forecast consolidation in the industry, and that is indeed happening. In June, Bird bought Scoot, a San Francisco company, and its coveted city permit. In early December, Bird laid off about 18 original Scoot employees, according to Peskin.

A Scoot representative said the company “is proud to have always offered, and continue to offer, positions that pay well, provide great benefits and stock options, as well as training programs and room for growth.”

A week after Scoot’s layoffs, about 40 workers at Spin voted to unionize. A representative said the company will begin a collective bargaining agreement and plans to hire more employees. Ben Barnett, a Municipal Transportation Agency spokesman, said his agency strongly supports the right of workers to unionize and is pleased Spin signed an agreement with Teamsters Local 665 to remain neutral on worker unionization. The other three companies have not signed.

“We don’t know whether these jobs are going to exist five or 10 years down the road, whether scooters are a passing fad,” said Doug Bloch, political director for Teamsters.

Mallory Moench is a San Francisco Chronicle staff writer. Email: mallory.moench@sfchronicle.com Twitter: @mallorymoench