Is there a database of traffic signals latitude and longitude? It would be neat to write a game that kept track of when you were stopped at these waypoints.
In theory, the maps provided by OpenStreetMap can also include positions of traffic lights. Note: Data is most detailed in Germany, not so much in the US. (If you use the programming language R, you might want to look at the osmar package to retrieve the data.)
Arlington County and Alexandria, Virginia both have a Traffic Signals dataset on their respective Open Data ArcGIS portal.
Arlington County, Virginia: