Teo, Jeff Y., and Erik all sent along this video of “rush hour” at an intersection in Utrecht, Netherlands quite crowded with vehicles, but most of those are bicycles.
According to the video description, 33% of all trips in Utrecht happen by bicycle. This video shows a place where a bicycle road crosses a busway and light rail line.
Separated bicycle paths could eventually bring this level of bicycles to DC commuting. Teo notes that the Capital Crescent Trail does get very crowded during rush.