Niels H. Christensen on Semantic Web Recipes presents how to load and parse linked-data and render in conjunction with Google Charts. He consumes a sample government API that supplies bus transportation data. This walkthrough formatted how-to is fit with code examples to aid the reader.
As a DC-area resident, I've been one of many local developers saying that the DC Metro needs some sort of API. If anything, just to be able to build or integrate transit routes into existing apps. The wait appears over and the Washington Metropolitan Area Transit Authority now has an API.