San Francisco officials, who rejected electric scooters after an unruly, unlicensed rollout a year ago, are now cottoning to the two-wheel devices under a yearlong trial that limits their numbers. Midway through that trial, the city is poised to consider next week whether to double the number of street-rented scooters it allows.

The free-for-all when three companies suddenly unleashed the rental devices last spring led to thousands of residents hopping aboard, and also triggered thousands of complaints. Scooter riders zoomed down sidewalks and bike lanes and weaved in and out of crowds. Abandoned devices sprawled across rights of way or were tossed into trash cans and in front of Google buses. The city temporarily banned scooters while it considered what to do.

The clampdown was partially lifted under the pilot that started Oct. 15. Two San Francisco startups, Scoot and Skip, have permission to rent 625 devices apiece, although most days Scoot offered far fewer. Usage of both companies’ vehicles plunged during the rainy winter months, making scooter sightings sporadic.

The San Francisco Municipal Transportation Agency, which oversees the pilot, next week will decide whether to increase the scooter allotment to 2,500 for the next six months. Tom Maguire, the agency’s director of sustainable streets, declined to say if staff will recommend that. However, he said, even if it allows more scooters, the agency is likely to stick with a directive issued in August limiting the pilot to two companies.

“We’re encouraged by how it’s going,” Maguire said. “We’ve seen the positives of moving from a Wild West scenario to some appropriate local regulations — a decrease in sidewalk riding and illegal parking on sidewalks.”

Several spurned operators, including Spin, Lime and Uber’s Jump, had appealed their rejections, while Lyft wrote letters asking for reconsideration. All had hopes of being tapped for the program’s second half.

From riders’ perspective, fewer scooters makes the rentals less useful, according to people who attended a public workshop held by the agency this month.

“I used to use them and loved them — then they disappeared,” said Soni Mehra. “It’s harder and harder to find them now, so I can’t rely on them to get to work.”

Both Scoot and Skip said they’d be happy to increase their fleets, especially now that they’ve ironed out some kinks — notably preventing theft and deterring some vandalism by adding built-in locks to all scooters as of early February.

Locks also ensure that parked scooters aren’t tipped over and don’t block sidewalks, curb cuts or crosswalks as they have to be affixed to bike racks or posts.

“The locking is key,” Maguire said. “We’re the first city in the country that has all our scooters lockable.”

Complaints about improper parking have plunged since the locks were implemented, he said.

Scoot had only a fraction of its allotment on streets for the program’s initial months because theft was so rampant, but now is bringing its numbers up.

“We had a rough start with all the theft and vandalism and then a terribly rainy few months,” said Michael Keating, Scoot CEO. “We want to show that this can be done safely, respectfully and sustainably.”

Skip CEO Sanjay Dastoor has the same goals. Both executives said it’s clear that demand currently exceeds supply. So how many scooters could San Francisco accommodate without returning to last year’s chaos?

“That’s a key question — how to expand the program without it being overwhelming,” Dastoor said. “Even doubling the number won’t create the level of reliability that residents and visitors expect to be able to depend on this as a mode of transportation.”

Keating said, “We think the city should continue to increase the number allowed until it’s clear they’re not being ridden that much. I don’t think anyone knows what the maximum number should be.”

Both companies and the MTA say they’re encouraged that scooter riders say they often turn to the devices to replace car trips.

“People are using this in a way we think improves the city,” Dastoor said.

Of some 1,700 riders polled earlier this year, 36% said otherwise they would have taken Uber or Lyft, while 5% said they’d have driven alone. Of the rest, 31% would have walked, 11% would have used public transit, 9% would have biked and 8% were “other.”

On their most-recent trip, 34% of respondents used scooters to get to or from public transportation, the transportation agency noted. Its conclusion: “Scooters induce transit trips at roughly four times the rate that they replace transit trips, indicating that they could complement transit by serving as a valuable last-mile connection.”

The MTA still wants more outreach to low-income riders. Fewer than 1% of scooter users take advantage of an “equity access” program to subsidize rides for low-income residents, even though about 9% would qualify. Regular rentals cost $1 to unlock plus 15 cents a minute; subsidized rides are half price.

The survey did reinforce some stereotypes about who rides scooters. Respondents were overwhelming male (82%), white (63%) and affluent (68% had household incomes above $100,000).

Carolyn Said is a San Francisco Chronicle staff writer. Email: csaid@sfchronicle.com Twitter: @csaid