In March, Seattle shut down its bike-share system. The decision capped a perplexing, embarrassing saga for a major city that consistently ranks near the top for bicycle commuters per capita. Seattle’s Pronto launched in March amid bike-share systems’ ascent from urban novelty to legitimate transportation technology, one that last year served up 28 million U.S. rides in more than 50 cities. But Pronto, with its small coverage area and fleet of just 500 bikes, never outgrew its training wheels. The system underperformed even for its size, recording less than one ride per bike per day. Scapegoats included the city’s rainy weather, its hills, and its mandatory-helmet law—who carries a helmet around? Now the docks have been removed; the bikes are being sold.

Then, in July, Seattle took a gamble on an innovation that has transformed China’s largest cities: dock-less bike share. Seattle permitted three private companies to deploy nearly 9,000 bikes on its streets, sidewalks, parks, and … everywhere else you could conceivably imagine a bike. The city suddenly has the second-largest fleet of shared bicycles in the United States, after New York. Riders make tens of thousands of trips daily. And it didn’t cost the city a dime.

These bikes—bright, light, and a little dinky—have swarmed U.S. cities from the Puget Sound to Biscayne Bay. They threaten to fill every inch of urban public space with hundreds of thousands of plastic bikes. But they also promise to permanently alter the way people move around the American city. And it might take a bit of that guaranteed civic clutter to get the job done.

It is easier to take a photo of 1,000 discarded bicycles than 60 million rides a day.

Just look at China. Perhaps it was only a matter of time before the country’s unprecedented pace of urbanization produced something revolutionary. For the past twelve months, Chinese cities have been in the midst of a spectacular and sometimes messy experiment: Millions of privately funded bicycles that can be ridden for a song and left anywhere at all. Most bike-share systems have docks where the bikes are stored. The docks tell you where you’ll find a bike and keep the bikes locked up when you’re done. In China, by contrast, the bikes are simply everywhere, secured by locks and GPS chips.

“Dock-less is as important to transportation as cellular was to telephony,” said Horace Dediu, an analyst at Asymco who studies the mode. It is the one place in the field, he said, where “change is happening at a blinding speed.”

More than 30 companies have delivered approximately 15 million bicycles to the streets of China’s cities. There are 1.5 million shared bikes in Shanghai alone, or about 1 bike for every 16 residents. If New York City—whose Citi Bike program is the largest bike share in the United States—were to match that ratio, it would need to multiply the number of blue for-hire bicycles by 50. In Xiamen, a city nearly the size of Los Angeles where the first major dock-less operator, Mobike, launched in December 2016, the ratio is even higher: 1 bike for every 11 people. That would be like if L.A. suddenly put 360,000 bicycles on the street.

These bikes are changing the way China commutes. Mobike claimed in May that its bikes had doubled the percentage of Chinese biking to work in selected cities, taking the share of bicycle commuters to more than 11 percent. The other major operator, Ofo, has drawn investments from e-commerce giant Alibaba and Didi, China’s version of Uber, as the company’s 2 billion 2017 bike-share trips started to eat into the short-distance ride-hailing market. Each company is valued at more than a billion dollars; each claims to be the biggest.

A backlash has already begun. In November, the country’s third-largest operator, Bluegogo, declared bankruptcy, prompting speculation that a bike-share bubble was bursting. Cities began to threaten companies for sowing disorder, or to simply impound bikes. Viral photos of bicycle graveyards, sites where hundreds of bicycles have piled up, seemed to announce a marriage of cheap cash and short-term thinking.

Of course, it is easier to take a photo of 1,000 discarded bicycles than 60 million rides a day. I asked David Levinson, a professor of transportation at the University of Sydney, whether dock-less bike share was a VC-funded bubble or the future of short-distance transportation.

“Yes,” he wrote back. “It’s like the internet in 1999.”

The industry shows no signs of slowing its expansion. Ofo reportedly secured another billion dollars in funding this month, joining Mobike and a handful of smaller startups on a push into cities in Southeast Asia, Europe, and the United States. Until this summer, Dallas was America’s largest city with no bike-share system; the arrival of several thousand bicycles operated by a handful of private companies has given it, overnight, one of the country’s largest fleets of shared bikes.

The most exciting thing for U.S. transportation planners? How cheap these bikes are to ride. Most services work out to around a dollar a ride. “Our job is to provide transportation options, and it costs a lot less to roll out,” Gabe Klein, who oversaw bike-share systems as transportation chief in Washington and Chicago, and now serves as an adviser to the dock-less company Spin.* “We saw this huge growth in D.C., I think we more than doubled bike mode share. Now we’re going to see that on steroids.”

In the U.S., bike-share systems tend to be a composed of a hodgepodge of different funders, vendors, and operators. No city has made a greater investment in old-fashioned bike share than Washington. But even there, planners have cautiously welcomed the competition. A handful of private dock-less companies have been permitted to deploy small fleets as a pilot program. In an ideal world, said District planner Sam Zimbabwe, “we’d have multiple operators reaching different market segments because of their pricing models.” On Friday, New York issued a call for its own dock-less expansion.

Why challenge the home team? In part because planners think mode share—the percentage of commuters who use bicycles—could be much, much higher. They don’t see multiple bike-share systems competing for the same pot of people. Rather, different systems can serve different markets. In spite of prices that can be a fraction of Capital Bikeshare, dock-less company LimeBike says all it needs to make its business model work is one ride per bike per day—a mark that most functioning bike-share systems fly by. (Capital Bikeshare clocked 5.6 rides per bike per day in October.)

A city blanketed in bicycles would address one persistent critique of bike-share systems: that the docks tend to be concentrated in central or otherwise well-off parts of town. “We don’t need to redline in a way that the dock systems redline cities,” said Chris Taylor, Ofo’s vice president of U.S. operations, referring to the midcentury practice of denying loans to black neighborhoods.

But in D.C., Taylor—who comes to Ofo from Uber—has been frustrated by the city’s regulatory approach for the pilot program, which has capped each company’s fleet at 400.* One reason Chinese systems are so popular is that there are bikes wherever you need them. But this has also been a source of friction. “The Chinese model depends on one huge subsidy, an invisible subsidy, and that’s the parking subsidy,” Dediu said. “The city is essentially granting free parking to all these bikes. If you add it all up as urban land, the amount of subsidy is in the trillions of dollars.”

In American cities, only private automobiles are entitled to that kind of real estate. (San Francisco, to take a city that is neither large nor particularly famous for driving, has 280,000 on-street parking spaces.) The bikes have already raised hackles. “Dallas can’t handle bike share. It’s turning our city into a bicycle junk yard,” one of the city’s morning-show hosts griped in October. (The city says there have not actually been many complaints.) To counter that problem, Mobike uses a scoring system in which riders rate previous riders’ parking jobs—leave a bike in a lake and your next ride will cost more. Nevertheless, Chinese cities are moving toward creating parking zones for the things.

The dock-less phenomenon has drawn comparisons to the arrival of Uber and Lyft, whose radical impact on urban transportation is difficult to separate from a consumer-friendly price war enabled by a massive venture capital subsidy. Like the ride-hail startups, they are also gathering valuable data about user behavior. But the similarities end there. Mobike and Ofo manufacture, own, and manage massive fleets, which (theoretically, at least) requires attention to maintenance, geography, and customer service.

Critics aren’t sure that the model can work, unadulterated, in U.S.

cities. In addition to the burbling outrage about misplaced bicycles, there are geographic challenges. American cities sprawl. While most automobile trips are short, driving and parking remain cheap and easy; there are few transit commuters to whom the “last-mile” problem means anything.

And then there’s that awkward question: Do dock-less bikes render the systems that U.S. cities have built out—working with nonprofits, sponsors, and grants—obsolete? Most experts say yes. Most American transit officials aren’t so sure.

In Minneapolis, Nice Ride Minnesota—a nonprofit bike-share system with 200 stations—put out a request for proposals to bring dock-less bike share to the city. “We did not see this coming at all,” Bill Dossett, the executive director, says of the dock-less bike explosion. After the past year, the potential cost savings—particularly on the electronic components of docks, from touch screens to key pads to lock motors—was too promising to ignore.

And so Nice Ride will hedge. The docks and bikes are coming back out in the spring, but the organization isn’t spending money on new stations. Instead it’s choosing between LimeBike and Motivate, the operator of the country’s largest docked bike-share systems, to undertake an expansion of several thousand free-floating bikes.

“Working to protect an old business model is a dead-end street,” Dossett explained. “But we want to keep out system going until we’re really sure that what’s going to replace it is going to stick around.” Even if the free-floating bikes could rival established systems for reliability, Dossett said, he foresaw a coming use for those docks: securing and charging electric bicycles, which many bicycle professionals believe are—after dock-less bikes—the next big thing.

*Update, Dec. 18, 2017: This article has been updated to reflect Klein’s affiliation with Spin.

*Correction, Dec. 19, 2017: This article initially misstated the District of Columbia’s fleet limit was 300; it is 400.