Electric scooters will roll again in San Francisco within six weeks, starting a new phase of a transportation revolution that became a brief sensation this spring.

The city has selected two San Francisco startups, Scoot Networks and Skip, to offer dockless rentals of 1,250 electrified stand-up scooters (625 each), starting by Oct. 15, the San Francisco Municipal Transportation Agency said on Thursday.

Scoot’s bright red scooters and Skip’s yellow-and-black ones got the nod based on those companies’ assurances that the vehicles will be ridden and parked without disturbing sidewalk users.

The companies say they will provide access to low-income users, share data with San Francisco, and protect users’ privacy, among other criteria.

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“It’s a good day in scooterland,” said Scoot CEO Michael Keating. “We’re excited that this vehicle will bring a whole new group of people into scooting as it’s so approachable and easy to ride.”

Sanjay Dastoor, Skip’s CEO, said he wants to a build a sustainable transportation company. “We feel really fortunate to serve our hometown,” he said. “San Francisco has been thoughtful about the permit process to make sure it serves everyone and there are opportunities for dialog and feedback.”

A dozen companies vied for up to five slots under a pilot program the MTA developed in June after a deluge of scooters touched off controversy. The year-long pilot includes the option to double the number of scooters to 2,500 in the second six months, at the MTA’s discretion.

The decision Thursday spurned some high-profile contestants, including ride-hailing companies Lyft and Uber, whose Jump e-bike subsidiary applied, as well as scooter companies Lime, Bird and Spin, which unleashed their vehicles here in March. The other unsuccessful contenders were Hopr, Ofo, Razor, Ridecel and Uscooters.

The MTA sought to balance acceptance of new ideas with protecting safety and access to the streets and sidewalks.

“We are open to the kind of innovation the private sector is bringing particularly if it can help reduce traffic congestion and improve performance of our (transit) system,” Tom Maguire, MTA director of sustainable streets, said at a news conference announcing the selection. “We expect private operators who operate in public right-of-way will serve the public interest.”

The MTA said it spent 10 weeks going over 800-plus pages of applications to rate companies across a dozen criteria related to safety, disabled and equitable access, community outreach, sustainability and their experience and qualifications.

Scoot, which already has a permit to operate Vespa-like, sit-down scooters in San Francisco, was the only applicant to require all users to watch mandatory training videos, the MTA noted.

“Scoot has a really strong history here in San Francisco coordinating with our agency in their shared moped service — we know they have that track record,” said Miriam Sorell, MTA senior transportation planner. Scoot also committed to developing a lock box so riders could reserve helmets along with their vehicles. It’s unique in providing scooters with batteries that can be swapped out for fresh ones, so its vehicles can be deployed around the clock, instead of having to be removed at night for charging, she said.

While a bill approved by the Legislature this week and sent to Gov. Jerry Brown’s desk would allow helmetless riding, wearing helmets is still important for safety, the MTA noted.

Skip, which rents scooters in locations including Washington, D.C., San Jose, Berkeley, Oakland and Portland, Ore., was the only company to propose creating a community advisory board, the MTA said. It also has a team of ambassadors to approach users about safe operations and offer them helmets.

Both companies are working on locking mechanisms, which would help prevent parked scooters from blocking sidewalks. While those will not be initially available, the MTA said it’s committed to working with the companies to implement lock-to systems as soon as possible.

Sources said that Lyft and Uber’s Jump subsidiary were rejected because of perceived transgressions in those companies’ ride-hailing operations, as The Chronicle previously reported. However, the city of Santa Monica picked Lyft and Jump, along with Bird and Lime, to run e-scooter rentals there, in a decision announced Thursday.

MTA’s scorecard for Lyft and Jump cited “the history of violation of traffic laws by ride-hail contractors.” Likewise, ratings for Bird, Lime and Spin said the MTA “negatively evaluates” their past violations in the city.

Spin’s application said it discussed its plans beforehand with the MTA, but Bird and Lime were perceived as following the “ask forgiveness, not permission” mantra originated by Uber and other disruptive tech companies.

The stand-up scooters are dockless, meaning they can be parked anywhere — which turned out to wreak havoc in the spring, as some riders left them sprawled across sidewalks. While some residents appreciated them as fun, cheap and convenient, others decried them for disturbing pedestrians’ right-of-way.

The city impounded wayward scooters, issued cease-and-desist letters to the three companies, and required them to stop operations on June 4.

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