Bing offers transit directions for 11 cities: Boston, Chicago, Los Angeles, Minneapolis, New Jersey, New York City, Philadelphia, San Francisco, Seattle, Washington DC, and Vancouver. For the official announcement, see the Bing Community Blog (Bing Maps Gets Transit Directions).
Microsoft is using General Transit Feed Specification (GTFS) data feeds in the application, the same data used in Google Maps. Transit directions should be part of every mapping application. The common GTFS standard and open data is enabling this broader integration and availability.
It is very promising to see the second major online mapping service add transit directions. I hope we’ll also see MapQuest and Yahoo! Maps follow along. As the Bing Maps transit directions feature develops and more agencies are added, I’ll post to the Trillium blog. I will also post as transit directions (hopefully) are added to other online mapping services.