Bike-sharing programs in Montréal, Paris, Barcelona, Melbourne, and Hangzhou, China, are transforming the way those cities function at rush hour, to say nothing of the collateral health benefits for their participants. In the United States, the most notable success story has been Capital Bikeshare in Washington, D.C., which has drawn acclaim for its convenient operations and admirable safety record: Only 24 reported crashes in more than 2 million trips. And when New York City launches the largest bike-sharing system in North America this month, it will demonstrate whether short-term, one-way rental bikes can fill a critical niche in one of America’s most demanding transportation ecosystems.

With an initial rollout of 7,000 bikes and over 400 docking stations in high-demand areas of Manhattan, Brooklyn, and Queens, Citi Bike builds on the burgeoning bike-path network spearheaded by New York’s Department of Transportation (DoT). Under DoT Commissioner Janette Sadik-Khan, Hon. AIA NY, the city plans to install 200 more stations and 10,000 total bikes by spring 2013. Given the environmental and public health advantages of cycling over motor vehicles, observers see transformative possibilities in Citi Bike. Its docking stations appear every few blocks at sites chosen through community input, and it’s a lot cheaper than cabs or even subways, with an annual membership fee of $95 (less than a one-month Metro­Card). Capital Bikeshare, operated by Portland, Ore.–based Alta Bicycle Share, is funded by the Congestion Mitigation and Air Quality Improvement Program. Citi Bike is supported by a $47 million partner­ship between Citibank and MasterCard. If it expands as steadily as planned, Citi Bike can be a game-changer in the nation’s largest city; and even though the bikes will be Citibank blue, the potential effects are exuberantly green.

In addition, Alta, having established a track record in Boston and Melbourne as well, has been selected to operate Chicago’s new system. The company’s Chattanooga system also opened in June. Alta’s bikes, manufactured by Bixi of Montréal, are built for urban conditions: Heavy-framed, with a step-through design, cargo basket, high handlebars, and self-powered, always-on LED headlights and taillights, they place the rider in a safe upright position with broad visibility, rather than a forward-leaning racing stance. Other systems, like Bike Nation in Los Angeles, DecoBike in Miami Beach, Nice Ride Minnesota in Minneapolis-St. Paul, and B-cycle in a dozen locations (including Denver, Des Moines, Iowa, and Spartanburg, S.C.) define a lively and increasingly crowded public–private economic sector.

Bike-sharing is affected by what economists call a network effect: A bike without ample destination docks would be as impractical as an isolated phone with no one to call. To that end, the Capital Bikeshare system has grown impressively, owing to Washington’s density, relative flatness, tourist base, and commuting patterns. Josh Moskowitz, who manages Capital Bikeshare, notes that its approximately 16,600 annual members largely represent D.C.-based commuters, while most of the more than 168,000 casual riders each year tend to be tourists or visitors. Whether each ride means one fewer car on the road is less clear. Alta president Alison Cohen loosely estimates that anywhere between 5 and 40 percent of rides would otherwise have been single-occupancy-vehicle trips.

In a 2012 report for Arlington County—which is across the Potomac River from Washington, D.C., in northern Virginia—Ralph Buehler, assistant professor of urban affairs and planning at Virginia Tech, notes that Capital Bikeshare trips are 50 percent more likely to replace walking and 35 percent more likely to replace subway trips than car trips. Mode-shift data are conjectural, but even if Capital Bikeshare is doing more to decongest Washington’s Metro subway system and sidewalks than to reduce vehicle-miles traveled, it is a welcome relief to commuters, since it thins out peak-time crowds.

New Yorkers accustomed to grim rush hours may expect a similar effect, but the biggest battle will be public opinion. Sadik-Khan has been something of a flak magnet, particularly among observers who see bikes as a passing and unsustainable trend. But her numbers don’t lie. Since she took office in 2007, the city has expanded its network of protected lanes, painted on-street lanes, and separated greenways to 700 miles. The measured cyclist population has doubled in the past four years, and the number of bike commuters has quadrupled over the past decade. Per capita accident rates among cyclists and pedestrians have fallen to the lowest figures seen since recordkeeping began a century ago. The streets are more accessible and noticeably safer, in part through design innovation and in part through the accompanying safety-in-numbers effect, as more motorists accept the need to share the right-of-way. “I think it’s all paid big dividends, and you’re seeing it on the streets,” Sadik-Khan comments. “People are voting with their pedals.”

In this atmosphere—with a loud political “bikelash” possibly fading after Neighbors for Better Bike Lanes and Seniors for Safety, two Brooklyn civic groups, unsuccessfully sued the city to remove the Prospect Park West bike lane—public approval of the lanes holds a solid majority, recently polling at 66 percent. Bike-sharing commands 72 percent support. There’s just one catch: greater physical exposure. Cars, trucks, and pedestrians unaccustomed to looking out for bikes while crossing the street pose a continuous risk to themselves and the bicyclists. The difference between a balanced ecosystem and bloodshed is about training, says John Pucher, who is a Rutgers University professor of urban planning and a co-editor (with Buehler) of the forthcoming book City Cycling. “Safety in numbers effectively could be the saving grace here, but I think there’s going to be a transition period,” he says, citing Paris bike-sharing program as a cautionary tale, where injuries rose by about 50 percent right after the city rolled out the 20,000-bike Vélib program too rapidly and with no training for riders (the injury rate has declined slightly since then).

Most NYC riders obey the laws, Pucher finds, but a few run red lights aggressively, endangering pedestrians and fueling the bikelash. The New York Police Department has been working with the DoT on an effort to improve practices among commercial cyclists by issuing summonses. But bike culture does not map neatly onto the city’s more ingrained car culture, and NYPD officers struggling to keep bike lanes cleared of delivery vehicles at times fail to keep the lanes cleared of their own patrol vehicles.

Transportation officials have promoted safety, multilingually, in restaurants and other businesses that pressure employees to accelerate deliveries by any means necessary, which includes riding on sidewalks. Fatalities are dropping amid the DoT’s “Heads Up!” safety promotions, police enforcement against speeders and drunk drivers, Transportation Alternatives’ “Biking Rules” civility campaign, and countless informal efforts by cyclists who see all too clearly the link between rogue riding and anti-bike sentiment.

Still, New York cyclists observe a destructive cultural gap in the so-called windshield perspective that makes many NYPD officers prone to give cars the benefit of the doubt while subjecting bikes to tactics ranging from neglect to borderline entrapment. Pucher cites cases where cyclists swerving to avoid illegally parked vehicles get ticketed for not using the lane. Such imbalances hardly bode well for the Citi Bike era, but it’s still early in the game.

“The bicycle is the most civilized conveyance known to man,” wrote novelist Iris Murdoch in The Red and the Green. “Other forms of transport grow daily more nightmarish. Only the bicycle remains pure in heart.” New York’s streets have long been more hospitable to nightmares than to purity of heart. But Washington and other cities offer valuable lessons for making room in the transportation ecosystem for Murdoch’s agile (if fragile) conveyances.