They appeared one morning in San Francisco, rolling in like the city’s iconic, chilling fog. They coasted through car-clogged streets at a brisk 15 mph, bearing a fleet of dorkish men and women in khakis.

Over the course of a few short weeks in March, the City by the Bay became one of several test grounds for these electric scooters, the latest deluge of mobility options from cash-rich companies offering yet another alternative to the traditional ways of getting around town.

There’s Bird, which also has scooters in LA, Santa Monica, San Diego, San Jose, and Washington, DC, and now more than 175 in the Bay Area.1 LimeBike runs dockless bicycle programs, too, but has its scooters in San Diego, DC, and SF. Spin has under 50 scooters in the Bay. Combined, they have more than $200 million in funding.

The scooters are very good for cities, their purveyors (and investors) argue. They don’t create traffic or emissions. They’re a convenient alternative to taking a car or relying on a not-so-vibrant public transit network. They’re pretty easy to use—download an app, locate a scooter, and go—and pretty cheap, often less than $2 per ride. And besides, they’re legal, because San Francisco’s rulers never thought to make rules regulating electric scooter sharing businesses. As with Uber and Lyft, circa 2010: Who’d even heard of such a thing, before it showed up?

Legal or not, they’re cause for concern, or at least headaches, in City Hall. Officials used to managing streets designed for cars are facing a bevy of new options that can create unseemly mess in a very limited space, even as they provide sometimes healthier, cheaper, and nimbler transportation alternatives.

Indeed, some corners of the city have reacted with alarm. People can lock the scooters anywhere on the street, and so they can easily impede wheelchairs, strollers, or people who appreciate the ancient art of walking. Users are sometimes not great at riding the scooters, especially in a place busy with cars, bicycles, doggos, pedestrians, and the occasional delivery robot.

“They’re small, but they do take up space,” says Miriam Sorell, a senior transportation planner at the San Francisco Municipal Transportation Agency. “For those in a wheelchair or with a vision impairment, they could pose a hazard.” It’s not that the city is anti-scooter, she says. “We want to make sure people operate them safely.”

For cities, this raises thorny questions, ones that need answers as governments say they’re getting serious about non-personal-car sorts of transportation. Since 2010, hundreds of American cities, towns, and university campuses have installed docked bike-sharing systems. (The Bay Area’s Ford GoBike system, operated by the company Motivate, rolled out in earnest just eight months ago.) In 2017, dockless bike-sharing companies like LimeBike, the Chinese companies Ofo and Mobike, Spin, and Jump, mixed up the business model, nixing the places to park vehicles in favor of an unlock-n-go approach. San Francisco has even contended with delivery robots, which local politicians complain can clog the streets. Cars usually get a few lanes, but there’s only so much sidewalk. Now cities have to make room for scooters, which not only park in the public right-of-way, but are sometimes (illegally) piloted there, too.

So what should a city street be, for whom, for what? Who gets to determine the answer? And are we cool if some private companies make money off it?

California state law provides some guidance. Electric scooter riders must wear helmets, possess driver's licenses, and stay off the sidewalk, leaving that strip of concrete to the people on foot. (Washington, DC, where e-scooters have operated since February, has similar rules.)