Diego Jaramillo adds a Capital Bikeshare bicycle to a docking station in Washington in November. Cycling advocates worry that a bill in the Maryland legislature that would require all bike riders to wear helmets would hinder the program as it expands to Montgomery County. (Andrew Harrer/Bloomberg News)

Their national association says you should wear one, a federal watchdog says you’re more likely to be killed without one and 21 states insist that kids use them, so it figures that most cycling advocates would salute a proposal to mandate that everyone use bike helmets in Maryland.

They don’t.

This was not a happy decision for cycling groups deeply entrenched in the karma of safety first, because they all agree that strapping your head into a plastic foam cocoon is the single best protection against going kerplunk.

But they worry that a House of Delegates measure requiring helmet use for all Maryland bicyclists would keep some people from riding at all. They also argue that there is safety in numbers, too — the more drivers see cyclists on the road, the more apt they are to be alert for them.

“It is really an awkward position and one that is difficult to explain because we are fully supportive of the use of helmets and encourage everyone who rides a bike to use one,” said Shane Farthing, executive director of the Washington Area Bicyclist Association. “We’re just not convinced that a mandatory helmet law is going to improve safety. In fact, we fear that it will undermine overall ridership by limiting the safety-in-numbers effect, [that it will] actually have the opposite impact.”

The cycling boom in the first decade of this century brought a 57 percent increase in the number of people commuting by bike and continued enormous growth in the number of adult recreational cyclists. It has been estimated that 67 million Americans ride bikes and close to 30 percent of households own more than one.

As cycling gained popularity in the 1990s, more riders began to die in accidents. But the numbers reversed and reached a 17-year low of 616 killed in 2010. Of that number, 70 percent were not wearing helmets, federal data show.

The Centers for Disease Control and Prevention says helmet use reduces head injuries by 80 percent, and the League of American Bicyclists says people should “never ride without one.” The District and Maryland — but not Virginia — mandate that riders under age 16 wear one.

“We feel that everyone should wear a helmet,” said Carol Silldorff, executive director of the nonprofit group Bike Maryland. “We don’t feel that it should be necessarily the law that you have to wear a helmet.”

Her group decided it would neither support nor oppose the bill to require helmet use. They are pushing other bike safety laws sponsored by the same legislators and scheduled for a hearing before the same committee on the same day.

“We want to have as positive as possible a relationship with these folks,” Silldorff said.

The bill’s lead sponsor, Del. Maggie L. McIntosh (D-Baltimore), said there once were warnings that requiring motorcycle helmets would deter people from riding, but “you still see plenty of motorcycles on the road.”

An avid cyclist herself, McIntosh said she has been surprised at the opposition to the bill by bike groups.

“I’ve had a whole lot of people walk up to me and say they’re shocked at the reaction of their bike clubs, and I think a lot of delegates are shocked, too,” she said. “If the only reason you’re riding a bicycle is to feel the wind in your hair, you should take up another sport.”

The Capital Bikeshare program that has been wildly popular in the District and Arlington County is about to expand into Montgomery County this year, and there are whispers that Prince George’s County and Baltimore may be the next to embrace it.

The program allows cyclists to pick up bikes from so-called docking stations all over town, use them for short hops and return them to any docking station within the system. Bikeshare does not provide helmets, so riders who prefer to wear one must carry their own.

Chris Eatough, who bikes from his home in Silver Spring to his job as manager of Arlington’s bike program, said a helmet law would be a “huge obstacle to the bike movement in Maryland.”

“If there was a helmet law, when Montgomery County adds [bikeshare docking] stations, they probably could take some measures to provide helmets,” Eatough said. “Helmet kiosks are in development, or selling cheap helmets at convenience stores is another option.”

Perhaps, says Farthing, but he worries that officials might become skittish about bikeshare expansion for fear that they would be legally liable if riders violated a helmet law.

“Is there some risk-averse administrator who won’t go forward with bike sharing until they have addressed the need to provide helmets?” he said.

Alexander Meller, an avid bike rider and racer, carries an extra helmet in his car trunk for anyone who shows up at a training ride without one. But he is opposed to the bill that would require them, in part because he fears it would divert the focus from distracted driving, which he says is a much greater risk to bicyclists.

“It’s also going to require a large underclass currently relying on budget [bikes] ridden on the sidewalk, into targets for ticketing and police harassment, unless they also buy helmets,” Meller said.