PHILADELPHIA Christina Tierno started riding her bicycle into central Philadelphia during November's city transit strike, and she hasn't looked back.
Even when the strike ended and buses started running after a week, Tierno kept riding her bike, inspired by the discovery she could save time, money and, in her own small way, the planet, by using pedal power to get to work or school.
Tierno, 25, a University of Pennsylvania graduate student, says the three-mile (4.8-km) commute from her West Philadelphia home saves at least $15 a week in bus fares, cuts about 10 minutes off her trip, and makes her feel stronger and fitter.
She is one of a growing number of Philadelphia residents riding their bikes for transport -- as opposed to recreation -- in response to efforts by city government and local campaigners to make Philadelphia a more bike-friendly city.
According to the Bicycle Coalition of Greater Philadelphia, bike use in the city has more than doubled since 2005, a trend it attributes to higher gasoline prices, growing concern over climate change, creation of bike lanes, and what it calls a "growing urban bicycle culture."
Throughout the nation, the number of people bicycling to work has increased 43 percent since 2000, according to the U.S. Census Bureau, as more cities encourage residents to recognize the benefits of using their bikes for transportation.
Among U.S. cities, Portland, Oregon showed the biggest gain, tripling its proportion of bike commuters between 2000 and 2008 to a nation-leading 6 percent. Seattle, Minneapolis and Sacramento also had relatively high rates.
Philadelphia's rate rose to 1.6 this year from 1.2 percent in 2006.
But the U.S. bike-commuting rate of 0.55 percent pales in comparison with European cities such as Amsterdam, where 28 percent of all personal journeys are done by bike, and Denmark where the national figure is 20 percent, according to the International Bicycle Fund.
Elizabeth Kiker, vice president of the League of American Bicyclists, said America's low rate of bike use is largely due to an "entrenched car culture." But she argued that Europe had its own love affair with the automobile in the 1970s and has since posted big gains in urban cycle use.
Kiker attributed growing U.S. bike use to rising gasoline prices, an increasing public desire to aid the fight against climate change, and a recognition that regular bike riding can help counteract America's obesity epidemic.
"Biking is a great way to include your daily workout in your routine, and it's a lot cheaper than a gym membership," she said.
In Philadelphia, whose government has declared that it wants it to create the "greenest city in America," campaigners are working to overcome widespread public concern about the safety of cycle commuting.
The city's bicycle coalition holds workshops that advise would-be riders on issues such as street hazards, lane positioning, helmet-wearing, and the fact that a bike is a legal vehicle
Philadelphia recently created an east-west bike corridor by establishing bike lanes on two central streets, an experiment that is expected to become permanent due to its heavy use.
"If you build it, they will come," said Breen Goodwin, the coalition's education director.
Tierno says it required some courage at first to commute amid the traffic, particularly since she comes from suburban Connecticut where bike lanes are unknown and the automobile reigns supreme.
But now she enjoys the challenge and has learned to assert her rights as a road user. "I have not had many problems with drivers," she says. "I just occupy a lane as if I was a vehicle."