This has been an epic year for bike-share in America. According to a report from the Earth Policy Institute, the opening of Bay Area Bike Share yesterday brought the cumulative size of the bike-share fleets in U.S. cities to 18,000 bikes, more than twice what it was at the beginning of 2013.

There are now 34 modern bike-share systems across the U.S. in cities as varied as Chicago, Miami Beach, and Chattanooga, Tennessee, EPI’s Janet Larsen writes in Grist. By the end of next year, Larsen anticipates the number of shared bikes available to the American public will have doubled again.

The year-to-date numbers in 2013 have been bolstered by the opening of New York’s Citi Bike, with 6,000 bikes, and Chicago’s Divvy, with 1,500. Both cities intend to grow their systems substantially. Several smaller systems launched in 2013 as well, including ones in Aspen, Columbus, Fort Worth, and Salt Lake City.

Still, the scale of bike-share systems in U.S. cities trails the size of leading networks in Asia and Europe, Larsen writes. Citi Bike is North America’s largest bike-share system, but it barely cracks the top 20 list of the world’s largest. In first place is Wuhan, China, with 90,000 bikes.