Why are two-thirds of Philadelphia bicyclists men, and what are we going to do about it?

The recent boom in cycling, here and around the nation, has been largely fueled by guys.

Between 2005 and 2010, the average number of bikes counted per hour at 17 Philadelphia locations grew by 127 percent, while the percentage of women riders decreased from 38 percent of the total to 32 percent.

Nationwide, the percentage is even lower: In 2009, women accounted for just 24 percent of all bike trips, according to federal data. That's down from 30 percent in 2001.

Between 2001 and 2009, the number of annual bike trips in the United States increased from 3.3 billion to 4.1 billion. However, the number of annual bicycle trips by women declined from about 1.1 billion to 1.0 billion.

That contrasts sharply with the experience in some European countries, such as the Netherlands (55 percent of bike trips are by women) and Germany (49 percent).

In Philadelphia, where biking by women is higher than in most cities, the percentage of female cyclists has held steady at about 33 percent for the last two years, according to the Bicycle Coalition of Greater Philadelphia, which conducts the annual counts.

Safety concerns are a major deterrent for women, said Katie Monroe, who is leading an effort by the Philadelphia bicycle coalition to increase the number of women on bikes.

Dedicated bike lanes are especially important in attracting female riders, she said.

Carolyn Szczepanski, director of communications of the League of American Bicyclists, cited the same need recently on the league's website: "The stagnation in cycling by women . . . shows that much more needs to be done to meet the specific needs of women, especially their desire for safe, convenient, and comfortable cycling facilities."

Philadelphia's bike lanes on Spruce and Pine Streets, installed in 2009, have a smaller gender gap than the city's streets in general, according to the bicycle coalition. About 37 percent of riders are women on streets with buffered bike lanes, compared with 23 percent on streets with no bike lanes.

Women are an "indicator species" for bike-friendly cities, according to researchers, since they are more risk-averse than men and more likely to stay off streets they perceive as unsafe.

Figure out what women want and you'll boost urban bicycling in general, say researchers.

"There can be no question whatsoever that the key to getting more women on bikes is providing safer, more convenient, and more comfortable-feeling cycling facilities," said John Pucher, a professor in the Bloustein School of Planning and Public Policy at Rutgers University who has written extensively about biking and walking. "And virtually all studies show that that requires more protected bike facilities that separate cyclists from motor vehicle traffic. Bicycling infrastructure and programs should focus much more on the needs of women than they currently do."

"And it's not just a matter of getting more women on bikes," Pucher said. "Cycling facilities protected from motor vehicle traffic are also crucial to getting any vulnerable or risk-averse people on bikes, but especially children, seniors, and anyone who is not yet an experienced cyclist. So protected bike lanes are also crucial to increasing the overall level of cycling in a city."

In addition to safety, women are interested in practicality. More often than men, women say they don't have time or can't carry the passengers or packages they need to on a bike, according to a 2010 survey.

"Women are responsible for a lot more child care and errands that make it hard to do all your daily travel by bicycle," said Monroe, 23, who wrote her undergraduate thesis at Haverford College on the role of gender in the Philadelphia bicycling world.

She also said that the competitive and male-dominated culture of cycling can be unwelcoming to women, and that some women are put off by bike shops that don't take them seriously.

So the Philadelphia bike coalition is sponsoring women-only rides, classes in urban riding, a website (www.womenbikephl.org), a Facebook page (Women Bike PHL), and other efforts to boost female ridership.

Cycling advocates need to reach younger and older women if they're going to boost the number of riders, she said.

Monroe, who was a Girl Scout for 10 years, has designed a program for scouts to earn a cycling skills and safety badge that can be adopted by local troops.

"Sometimes we have a perception that [a woman cyclist] looks like a twentysomething. But the cool thing is that you can do it at any point in your life," said Monroe, who has named her old green bike Helena in honor of her grandmother Helen Monroe, who rode the bike well into her AARP years.