To visit Bogotá, Colombia, on a Sunday is to witness an unforgettable spectacle: miles and miles of car-free streets packed with cyclists, runners, and walkers.

Last summer, I walked from my hotel down a hill to Carrera Séptima, a wide avenue where men on Italian road bikes zoomed past teenagers on mountain bikes. Grannies on rusted cruisers glided alongside dog walkers. Together, they formed a torrent broken only when a few people periodically peeled off to sip papaya juice from a vendor on the sidewalk.

From 7 am to 2 pm every Sunday (and holiday), 76 miles of streets are closed (partially or fully) to traffic for the Ciclovía, a program the local government has run since 1974. Some 1.7 million people, or about a quarter of the city’s population, turn out for it on average every week. Surveys have found that nearly half of people use the blocked-off streets for at least three hours.

Having the time and the space to exercise is increasingly a luxury for city dwellers, and rates of chronic diseases linked to physical inactivity are disturbingly high. So a weekly, city-sponsored recreation event seems like a brilliant idea. And, indeed, the Ciclovía is the largest, most frequent mass recreation event in the world.

Word of it has gotten around, and more than 400 cities worldwide are now attempting their own radical acts of car traffic suppression. As with the superblocks of Spain, it’s a sign that urbanites are seeing their streets as spaces that can be lived in.

In September, Paris allowed people to cycle and walk on 400 miles of roads closed to traffic in the second annual Journée Sans Voiture. The day before, Philadelphia held its first Philly Open Streets, with 10 miles of streets blocked off for cyclists and pedestrians. A section of San Antonio, Texas, was car-free that day, too. (Philly’s event came after an enthusiastic response to road closures during the pope’s visit last year.)

Ottawa now offers 32 miles of car-free Sunday Bikedays from May to September. Mexico City, one of the biggest, most traffic-clogged urban centers in the world, has become a very pleasant place to cycle for a few hours each Sunday during Muévete en Bici, or Move Yourself on a Bicycle. Bangalore, India, and Cape Town, South Africa, have hosted successful events, too.

Health researchers say these programs get people exercising more than they otherwise would. They also draw people from different neighborhoods and economic groups together, reduce air pollution, and help galvanize cities around “active transportation” initiatives like bike lanes.

No one has yet been able to replicate the scale of what Bogotá has achieved. Other cities are finding that these events can be costly, logistical nightmares. Sometimes they fail. Yet momentum is building. “Open Streets is absolutely approaching a tipping point,” says Mike Lydon, principal of the Street Plans Collaborative and founder of the Open Streets Project, an advocacy group for the movement in North America.

How Bogotá showed the world how to open streets

Bogotá might never have had a Ciclovia if an activist named Jaime Ortiz Mariño hadn’t gone to the United States to study architecture and design in the late 1960s. In Bicycling Magazine, Ortiz Mariño described how he followed other students to Washington to protest the Vietnam War and learned the ways of social revolution:

I was educated analyzing this urban crisis [the rise of the automobile and the suburb]. When I came back home to Bogotá, I was shocked to see that we Colombians were following the American path of urban development. Cars and more cars. One person, one car. It was obvious that this was not going to lead to a livable city. So I became a radical. I knew how to do it: I was trained by the best American counterculture radicals. And the bicycle quite naturally became a symbol of revolution. The bicycle symbolizes individuality, civil rights, women's rights, urban mobility, simplicity, the new urbanism, and, of course, environmental consciousness.

Ortiz Mariño organized Bogotá’s cyclists, and in December 1974 they persuaded city officials to close two central streets to vehicle traffic. "Over 5,000 people came from all over to ride their bicycles down the middle of Bogotá,” Ortiz Mariño told Bicycling Magazine. “Housewives, hippies, executives, the young, and the old. The Ciclovía became the start of our movement."

The program picked up steam in the 1990s and early 2000s, under Bogotá Mayor Enrique Peñalosa and his brother Gil Peñalosa, who was then the commissioner of parks and recreation. Under Mayor Peñalosa, the Ciclovía route increased from 8 miles and 140,000 riders every Sunday to 70 miles and as many as 2 million people.

Critically, Peñalosa also developed the structure for the city to run the event, with volunteers, uniforms, signs, and marketing, as Streets Blog reports. It’s funded with a tax added to all citizens’ phone bills and by private sponsors.

“Over time the system has been perfected in terms of minimization of costs and of making the public aware of the road closures,” Marcela Guerrero Casas, a Colombian raised in Bogotá who is now the managing director (and co-founder) of Open Streets Cape Town in South Africa, tells me in an email. “When you do this consistently (in terms of time and location); people accept and embrace the program.”

The program also helps city residents achieve physical activity goals: According to one study, people over the age of 60 who lived near the Ciclovía route were more likely to walk 150 minutes or more each week — the recommended weekly amount of physical activity. Since 2007, the program also been a part of Colombia’s National Public Health Plan. And in 2009, it was written into the national obesity prevention law.

Word of what was happening on the streets of Bogotá slowly got out. Then came a film in 2007 in English by Street Films.

Though it was just nine minutes, the film circulated widely in urban planning circles. By 2008, says Lydon of the Open Streets Project, US cities were ready to try it.

America gets Open Streets fever

In the US, this idea wasn’t entirely new: Seattle has had Bicycle Sundays as far back as 1965. But in 2008, “all of a sudden it was a strong fascination of urbanists and bike advocates,” Lydon says. “If Bogotá was doing this, why couldn’t New York and Portland do it?”

That the Open Streets model would appeal to Americans is not surprising. US cities have plenty of their own car angst, air pollution, and limited public spaces for people from different neighborhoods to be active together. But what US cities did not have is a system for permitting and managing these events; closing miles of roads for cyclists and pedestrians to exercise is distinct from closing roads for street fairs, block parties, or marathons.

A handful of cities began trying it — first as one-off events, some building up to monthly events in the summer. As of January, 122 US cities had hosted Open Streets events, according to Aaron Hipp, an associate professor of community health and sustainability at North Carolina State University who has been studying the movement.

Some of the most popular events have been CicLAvia in Los Angeles, NYC's Summer Streets, Ciclovia Tucson, and Portland Summer Parkways in Oregon. “The movement is making incredible progress,” says Lydon. As evidence, he cites the Los Angeles County public transportation agency’s approval of $4 million in funding for 17 open streets across the Los Angeles region, up from the current 10 events. “That's a big deal,” he says.

Turnout at the first Open Streets events in Philadelphia and Detroit this September was also high, he says.

Today was pure magic. 8 year olds loved it. 80 year olds loved it. More Open Streets next year! @OpenStreetsPHL @PhillyFreeSts @PhillyMayor — 5th Square (@5thSq) September 24, 2016

It’s really expensive to close roads

Lydon has plenty of success stories to point to. But expanding Open Streets in US — getting new cities to try it and making the programs in the cities that already have them more frequent — means a lot more wrangling with funding, permitting, and marketing events to the public.

Many cities, including my home city of Washington, DC, have not been willing to host an Open Streets, in part because streets here are already subject to especially strict rules, despite ardent pleas from bike activists.

The No. 1 obstacle, according to Lydon, is money. One event costs a minimum of $10,000 and up to about $70,000 (what San Francisco spends). They are city-funded or grant-funded or a combination, but someone has to pay overtime for the police officers and traffic control aides to manage routes and intersections.

“Right now, it takes so much support [to do this in Los Angeles],” says Deb Cohen, an epidemiologist with the RAND Corporation who has studied the program there. “The police force is out, they have to block streets a certain way. It takes a lot of coordination.”

Some US cities that started these programs have failed to sustain them. After holding several events between 2008 and 2013, Chicago discontinued Open Streets in 2014. Organizers cited a lack of funds — the regional non-profit Active Transportation Alliance couldn’t raise the resources to keep it going. The final event in 2013 was mostly rained out, making it “an expensive disappointment.”

What Bogotá has done to bring costs down is build a large volunteer team of people who manage route closures. Los Angeles is in the process of doing the same.

Permitting can also be a major problem. Often, organizers have to get property owners’ approval along the routes one by one. Cities have standard permits to close roads for block parties, marathons, fireworks, and street fairs, but most don’t have them for Open Streets.

What US cities ultimately need, Lydon says, is a standardized system for permitting and route management that reduces the need for police to manage intersections.

Open Streets have to be regular to actually impact health

Open Streets events have reached 122 US cities. But 62 percent are one-offs rather than regular programs, according to Hipp’s research.

“We’d like to see a lot more cities doing it, but even before that, I want to see more frequency in the cities that already do it,” says Lydon. “Infrequency is a barrier to longevity and success — you’re not going to get the long-term impacts or behavior shifts that are possible if they’re just one-off events.”

One challenge is measuring and proving their value: Are they worth a city’s investment because of what they yield in public health? It’s hard to prove that, but a study published in the Journal of Urban Health tried to quantify the costs and benefits of Open Streets programs in Bogotá; Guadalajara, Mexico; Medellín, Colombia; and San Francisco based on 2009 data.

Specifically, they looked at whether the city saved on direct medical costs for every dollar invested in the Ciclovía program. In Bogotá, they found, the program costs users just 10 cents each and the city $6 per capita, while creating $3.20 to $4.30 in medical savings for every dollar invested. San Francisco’s Sunday Streets program, meanwhile, costs users $1.36 apiece and had a per capita cost for the city of $70.50, saving $2.30 in direct medical costs per dollar invested, the researchers found. Overall, they concluded that across the board, the programs were “cost beneficial.”

Health researchers studying CicLAvia in car-devoted Los Angeles have also shown that the program, which has been going since 2010, is having an impact. In a paper published this year in the journal Preventive Medicine, Cohen, the epidemiologist, and co-authors surveyed CicLAvia participants in 2014 to track their numbers, how far they’d traveled to participate, and whether the CicLAvia made a difference in their physical activity patterns.

Turnout was impressive: Some 310,000 people from across the region came, “a sign that this is a unique opportunity, worthy of significant effort to attend,” the researchers wrote. What’s more, 45 percent said they would have been sedentary if they hadn’t been walking, running, cycling, or skateboarding on the route. If made more frequent, the researchers wrote, the cost of coordinating the event could come down and it could “help thousands to meet the weekly recommended levels of [150 minutes of] physical activity.”.

Researchers have also found that in Bogotá, the Ciclovía is making a difference in people’s weekly exercise routines. A 2009 survey found that 42 percent of adults got at least 150 minutes of exercise during the event. Only 12 percent of participants said they would have gotten the same amount of exercise another way.

It’s easier to evaluate — and justify the expansion of — the better-established programs. Other cities aren’t there yet. “In our case, presenting a convincing case to government when there are so many other pressing issues is tricky,” says Guerrero Casas in Cape Town. “We need time (and regularity) to prove the impact but also need the data to prove its potential. It’s a Catch-22.”

Open Streets are ultimately just one of many ways cities can encourage people to be active. Cities can build running and biking trails and parks and maintain and expand the ones they already have.

Yet Hipp, the public health researcher, says Open Streets has a unique ability to change a city’s culture of health. And Bogotá remains the gold standard.

“To have any effect on transportation and physical activity behaviors and democratizing the streets, it’s going to have to be more like Bogotá,” he says. “In Bogotá, the route is long, it’s every Sunday and holiday, and it has main streets and neighborhood streets. Everyone can participate, because it’s everywhere.”

More cities need to study these successes and pursue them. I’m looking at you, Washington, DC.