The expanding program in Barcelona is typical of so-called third-generation programs, which rely heavily on technology. (In its first generation, bike-sharing involved scattering old bikes around the streets, where they could be used for free; second-generation programs accepted coins.)

Here, a customer buys a yearly membership for about $30 and is issued a smart card that allows the rider to remove a bike from a mechanized dock. The first 30 minutes are free, with a charge of 30 cents per half-hour after that. A bike must be returned to any bike rack in the network within two hours or the card may be deactivated.

Most programs in Germany and Austria work on a different system; members receive cellphone text messages providing codes to unlock the bikes.

Copenhagen and Amsterdam have had devoted bicycling commuters for many years. But the new programs have created the greatest transportation revolution in central and southern Europe, where warmer climates allow riders to ride comfortably year-round. The shared bicycles in Barcelona, Lyon and Paris are heavily used, logging about 10 rides a day, according to officials in these cities.

In North America, issues like insurance liability, a stronger car culture, longer commutes and a preference for wearing helmets have slowed adoption of bicycle-sharing programs. None of the European programs require helmets. Still, Washington and Montreal are experimenting with small projects, and Chicago, Boston and New York are studying options.

Perhaps the best indication that bicycle-sharing has arrived is this: Shanghai, which 10 years ago was trying to eliminate bicycles from some of its boulevards to make way for cars, opened a pilot bike-sharing stand last month.

In most European cities, advertisers have been given contracts to set up and maintain bicycle-sharing programs in exchange for the rights to sell advertisements on city-owned structures like bus stations.