The most recent U.S. Census Bureau estimates show that about 730,000 Americans bike to work as their primary means of transportation, a 50 percent increase since 2000. This shift is most prevalent in large metro areas, with Denver, Portland, and Washington, D.C., among cities reporting the largest gains in bicyclists. Bicycle commuting is more common in densely populated areas. College towns, in particular, report high numbers of cyclists.
For more information: http://www.governing.com/blogs/by-the-numbers/bicycle-commuter-data-for-american-cities.html