Car-Free Day website suggests "bicycling, walking, teleworking, carpooling, vanpooling or taking transit." These are all excellent ideas. But what about skateboarding? With the Potomac River getting cleaner and greener, you might also consider swimming. Or even better, do a triathlon commute: run to the Potomac, swim across, and then grab a Capital Bikeshare to go the final distance.
Triathlon commuting is not just for an ironman. Ducks waddle, paddle, and fly. Anyone can waddle, paddle, and peddle.