Till Nagel and Christopher Pietsch have created an art installation that allows one to visualize and compare the spaces of flow created by bike-sharing systems in New York City, Berlin, and London. The name of the project is city flow, a comparative visualization environment of urban bike mobility. They have recently published a paper (co-authored with Marian Dörk) with more technical information about their project.
These guys are doing a fabulous work with design, and I believe they're really pushing the boundary of data visualization in urban and transport studies with new tools to visualize the space-time geography of flow data.
Take a look at how easy it gets to explore trajectories of cyclists in space and time with their tool.