But the majority won't consider the bicycle as a regular means of transport because they simply have too far to go and feel nervous about riding on traffic-choked streets, bicycling advocates and dedicated motorists say.

"It's never just a matter of picking up a few things you could carry on your bike," said Crystal Kelson, 33, a nurse and mother from North Philadelphia. "You need a car."

Kelson said there was no real alternative to her Dodge Charger -- which now costs her $65 a week in gasoline -- even for short trips to the supermarket.

According to the National Sporting Goods Association, the number of Americans who bike "frequently" -- 110 days a year or more -- fell almost 10 percent in 2007 to 3.7 million people.

Similarly, the number of people who ride bikes at least six times a year fell to 35.6 million in 2006, the lowest since the survey began in 1984, from 56.3 million in 1995.

Thomas Doyle, vice president of information and research at the association, said the decline was probably due to the aging population, reluctance by parents to allow children to ride bikes and more children using wheeled toys such as scooters and skateboards.

The proportion of personal trips made by bike is less than 1 percent, according to the League of American Bicyclists, a Washington-based advocacy group.

That compares with 27 percent in the Netherlands and 18 percent in Denmark, both of which have networks of bike-only paths, bike lanes and calm streets where people of all ages can feel safe riding.

SIGNS OF A TURNAROUND

Still, American bicycle advocates said there are signs the trend could be reversed, prompted most recently by gas prices, and by concerns over climate change, air pollution, energy security and personal health.

"All the indications are that people are looking at cycling and other transportation alternatives, and gas prices are pushing them to do that," said Andy Clarke, executive director of the League of American Bicyclists.

Some American cities including Portland, Oregon, and Washington have higher rates of bike use than the national average thanks to bike-friendly infrastructure.

In Philadelphia, the jump in gas prices has become the "tipping point" for getting more people on their bikes, said Alex Doty, director of the Bicycle Coalition of Greater Philadelphia.

He said bike use in the city rose 25 percent in 2007 and is up 6 percent this year, but only 1.4 percent of personal trips in Philadelphia are made by bike, compared with 30 percent in Amsterdam.

Jesse Gould, a salesman at Assenmacher's Cycling Center in Flint, Michigan, said more people are buying bikes for commuting.

"Gas prices give them a kick, but the big thing that makes them start riding to work is that they see their friends doing it," Gould said.

Edgar Gil bikes seven miles (11 km) to work in Washington from his home in Arlington, Virginia, every day. He will be making the trip -- about 60 percent of which is on traffic-free bike paths -- on Bike to Work Day to show seven coworkers how he does it.

Gil, 35, said biking saves about $100 a month in bus fares, and, despite the traffic and pollution, he simply likes to ride.

"You enjoy it more, you get to work relaxed," he said. "You have a better day."

Catherine Williams, a retiree, filled her Cadillac with $3.77 gasoline at a BP station in North Philadelphia for a 50-mile (80-km) roundtrip to the doctor's office. She said she uses public transportation when she can, but wouldn't feel safe on a bike.

"This is the US and people will kill you out there riding your bike," she said. "I would not take my life in my hands and ride a bike."