D.C. Bus Gets Real-Time Locator Application
"All you have to do is go to http://circulator.dc.gov/ from any mobile device (the url works in any browser, really), select the Circulator route and bus stop, and it'll tell you where the closest bus is."
As DCist notes, the utility of this service maybe limited, as the Circulator bus is set to run every ten minutes. However, many are saying this is a good step towards more open and accessible transit information.