Schedules and Trip Planning Data (GTFS)
GTFS, or the General Transit Feed Specification, is the standard format used by many transit agencies to release schedule and trip planning information. In addition to Google Maps, GTFS is at the heart for many MBTA trip planning applications. GTFS is a well-documented standard. Learn more at Google's documentation.
This feed contains information for all MBTA services, including bus, rapid transit, commuter rail, and ferries, as well as MassPort airport shuttles.
Getting the File
The MBTA GTFS file is delivered in a ZIP file. The file is located here.
It will remain available at the same URL. It is updated at least four times a year, but may change at any time. To ensure that you have the latest data without constantly downloading the whole thing you can download the current feed_info.txt file here and compare it to the feed_info.txt file from your last GTFS download. If the feed_version field is different then you need to update.