In a city where the mayor is often portrayed as a protective nanny, restricting cigarettes, fatty foods and sugary drinks, there is a glaring exception: a new bike-share program that allows riders to pedal through some of the nation’s busiest streets without a helmet.

The lack of a helmet requirement in New York’s month-old Citi Bike program, which eventually will accommodate as many as 10,000 cyclists — many of them tourists — has some experts predicting a disastrous increase in injuries and fatalities. Comedians have piled on, with “The Daily Show” host Jon Stewart sarcastically suggesting a “Street Brain Material Removal Service.”

But so far, through more than 500,000 rides, such predictions haven’t come true, with just three minor accidents and nothing more serious than some scrapes and bruises.

That’s done little to quell the debate over helmets, which officially are “encouraged but not required” in the program. Delivery cyclists and those 14 and younger are already required to wear helmets under New York state law.

“It is funny that helmets aren’t required. It’s definitely a worry,” said Alessandro Russo, a tourist from Rome who was considering taking a bike-share spin in lower Manhattan.

“It seems counter to logic not to require bike share participants to wear helmets,” said Robert Sinclair Jr., spokesman for AAA New York. “We are very worried about setting tourists loose on the busy streets of New York.”

When asked about the rationale for not requiring helmets, city officials repeated what they have said for months — that such a mandate would be impractical to enforce.

But even if helmets aren’t mandatory in New York, officials are taking steps to encourage people to protect themselves. The city aims to give away 20,000 helmets this year, and annual bike-share members can get $10 off a new helmet at any bike shop in the city.

Also, entrepreneurial newsstands have already started selling helmets along with papers, cigarettes and gum, and some hotels are offering headgear for guests to borrow.

City Department of Transportation spokesman Seth Solomonow noted that most cities with bike-share programs don’t require helmets and some have even repealed mandatory helmet use.

The reason, experts say, is that helmet requirements tends to dampen the popularity of bike-share programs by taking the spontaneity out of the decision to just hop on a bike and go. Casual riders and tourists would have to plan ahead to bring a helmet or buy one on the fly.

Melbourne, Australia’s bike-share program requires riders to wear helmets, and although the city is flat and ideal for cycling, it achieves only 10 percent of the usage of comparable programs in London and Dublin, which don’t require helmets.

Washington, D.C.’s bike-share also recommends but doesn’t require helmets, though riders have the option to buy one when they sign up. In Boston, people who want to use the “Hubway” bike share must sign a user agreement promising to wear a helmet at all times. Seattle plans to require helmets when it launches a regional bike share next year.

New York City’s privately financed program — called Citi Bike, after lead sponsor Citigroup Inc. — was a pet policy goal of Mayor Michael Bloomberg as a way to decrease the number of drivers on the road and encourage healthy lifestyles. It began late last month with 6,000 bikes at 330 docking stations, with plans to expand eventually to 10,000 bikes and 600 stations.

Riders can unlock the three-gear, cruising-style bikes from any station, take them for 45-minute rides and return them to any rack. Thousands of people have already signed up for $95 annual memberships for unlimited rides. A 24-hour pass costs about $10. Any profits will be split between the private operator and the city.

Despite the fact the city has laid down 300 miles of new bike lanes in the last five years, cycling in New York is still a proceed-at-your-own-risk pastime.

Speeding cabs, fume-belching buses, honking drivers and texting pedestrians turn even short rides into obstacle courses. Bike lanes blocked by parked cars, delivery trucks and even police cruisers have become another frequent source of aggravation, forcing cyclists into the thick of traffic.

“The bike lanes in New York are a joke compared to other cities,” said Jovon Grossi, a chaplain who has biked in cities all over the country. “There’s always cars double parked; people see the green lane and they think they can walk in it, run, skateboard. It’s definitely not a sacred space for bikes.”

A 2009 study found that New York’s bike lanes are blocked more often than not — during a 10-minute span, a cyclist has a 60 percent chance of being blocked by a car, truck or taxi.

Bloomberg spokesman John McCarthy defended the city’s bike friendliness, saying the most effective way to keep cyclists safe is separating cyclists from drivers, “which we have done more in this city than any other city in America.”

Although the number of people commuting by bike in New York has increased by more than 260 percent since 2000, the number of cyclists killed has remained steady, at around 20 each year. This means the risk of serious injury or death for those on bikes has dropped by 73 percent, according to city DOT figures.

Still, in 97 percent of bike fatalities from 1996 to 2005, the rider wasn’t wearing a helmet.

A lack of a helmet requirement, blocked bike lanes and inexperienced cyclists hitting the road are all reasons Rutgers University public policy professor John Pucher cited in predicting that the number of cyclist injuries and fatalities will double or even triple in Citi Bike’s first year.

But there is also research supporting the theory that bike-share schemes calm traffic because drivers are more cautious when cyclists are on the road.

The Mineta Transportation Institute in California studied 14 bike-share programs and found relatively low accident rates, averaging 1.36 serious or fatal accidents in 2011. In the same year, there were 22 fatalities for bicyclists in New York.

Dan Taeyoung, an architect, was putting his faith in that theory as he unlocked a bright blue Citi Bike and prepared to venture out helmetless at Columbus Circle.

“I normally wear a helmet, but these bikes are strong, visible, stable,” he said. “And the more bikes there are, the more drivers have to pay attention.”

(AP)