By MATT FLEGENHEIMER Nvember 4, 2013

To many, the ingredients for New York City’s bike-share program suggested a sort of sadistic alchemy.

Start with notoriously unforgiving traffic. Add thousands of bicycles along the city’s most congested corridors. And see how perhaps the world’s least understanding drivers would cope with the new additions.

And one more thing: Many of the cyclists would be helmetless novices — or worse, tourists — careening into and out of lanes with the whimsy of a youngster pedaling through a suburb.

As of Monday, though, after more than five months and five million trips, none of the program’s riders have been killed on the bikes. About two dozen injuries, most of them minor, have been reported.

Last year, according to the city’s Transportation Department, 18 cyclists were killed in car crashes from January through October, compared with 10 so far this year, though citywide, cyclist injuries have remained consistent. There was one cyclist death this year in the neighborhoods served by the bike-share program, in parts of Manhattan and Brooklyn, though the cyclist was not riding a Citi Bike. Over the same period last year, there were two bike deaths in these areas.

And while sidewalk cyclists, red-light-running cyclists and “salmoning” cyclists — those who ride against traffic — remain a daily scourge for many New York pedestrians, no one has been killed by a cyclist in the city since 2009.

The administration of Mayor Michael R. Bloomberg has attributed the good fortune to “safety in numbers,” arguing that the increase in bike ridership, even before the introduction of the bike-share program, has heightened drivers’ awareness of cyclists and affected their behavior.

“This notion of blood on the streets has not proven out,” Janette Sadik-Khan, the transportation commissioner, said in an interview.

There have been several dire forecasts since the program’s inception. Skeptics pointed to the grim beginnings of a bike-share program in Paris, where the population density was “virtually identical” to New York’s in many neighborhoods, according to a Bloomberg administration study in 2009.

Three riders died in the Paris program’s first year, and, citywide, bike accidents increased 7 percent, the study said.

Preparing for a similar start here, John C. Liu, the city’s comptroller, called for a helmet requirement, arguing that the city could face a spate of legal claims.

John Pucher, a professor of urban planning and public policy at Rutgers University and a longtime cycling advocate, said last year that he expected “at least a doubling and possibly even a tripling in injuries and fatalities among cyclists and pedestrians during the first year.”

The program also faced ribbing in the media; in a segment on the “The Daily Show,” Jon Stewart proposed a new business venture: “Jon Stewart’s Street Brain Material Removal Service.”

There is of course no guarantee that the system’s promising safety trends will hold. Some officials have expressed a skittishness about even discussing the numbers, perhaps recalling the recent example of the Police Department. Last month, shortly after the city celebrated a seven-day stretch in which no homicides were recorded, there were five within 10 hours.

But the Transportation Department said it was confident that its statistics, like the city’s homicide rate, were moving in the right direction. In a new report assessing recent street projects, the city trumpeted the successes of pedestrian plazas, bike lanes and remedies like “mixing zones” and curb extensions that have made pedestrians and cyclists more visible to drivers.

The report noted that traffic fatalities in the city had fallen 30 percent since 2001, though last year’s figure, 277, was the highest since 2008. (According to preliminary data, the total this year is down slightly, with 209 traffic-related deaths through September, compared with 218 over the same period last year.)

Charles Komanoff, a transportation economist and avid biker, suggested that the “safety in numbers” phenomenon had spawned a helpful cycle: The increase in biking in recent years has made the practice safer, which has encouraged bike-share ridership, which should in turn improve safety for “incumbent cyclists.”

Paul Steely White, the executive director of Transportation Alternatives, said some of New York’s drivers were beginning to behave like those in major international cycling hubs. “People just expect to see them around every corner and around every turn,” he said.

As the program enters its first season of cold weather, though, there is a lot more to prove. Mr. Pucher said in an interview last week that while he regretted predicting a doubling or tripling in bike deaths, he would be “really surprised” if future data did not reveal at least a modest increase in injuries.

Mr. Liu, affirming his call for mandatory helmets, said that “a great five months” did not “obviate the need for safety measures.”

But as an annual member, he said he had just one serious complaint. “The Citi Bikes come in only three speeds,” he said. “Slow, very slow and ultraslow.”