More numbers, from 2012:
While there aren’t more bikes than cars, there are more non-car commuter trips than car commuter trips in D.C. already. When you include transit, walking and cycling, non-car commuting makes up about 55% of all commuter trips.
http://www.theatlanticcities.com/commute/2013/10/us-cities-where-fewest-commuters-get-work-car/7390/
You can also see that bike commuting in D.C. rose from just over 1% of all trips in 2000 to 4% in 2012.
In NYC, two-thirds of commutes are done without a car. Their bike commute percentage is much lower than in D.C., but I suspect that the percentage has risen since Citi Bike started up.
Midwestern and Southeastern cities have much lower rates of non-car commuting, partly because many smaller cities do not have extensive mass transit systems or bike infrastructure.
But that is changing gradually. Even some smaller cities have started bikeshare systems over the past 12 months. Chattanooga is one. Columbus, OH is another.
http://www.bikechattanooga.com/
http://www.cogobikeshare.com/
Los Angeles, Long Beach and Santa Monica are discussing a possible regional bikeshare system for Southern California, although they have been running into some issues as they try to surf the bikeshare wave.