There are a number of mailing lists that can be good resources when you have questions about public transit data, software, formats like GTFS and GTFS-realtime, and other issues:
- transitfeed: discussion of the open-source transitfeed project, as well of discussion of the GTFS specification and associated tools.
- gtfs-realtime: discussion of the GTFS realtime specification.
- gtfs-changes: discussion of proposal for extending the GTFS specification, as outlined in the GTFS Changes document.
- transit-developers: general transit developer discussions. Many transit agencies also have their own developer mailing lists specific to the agency. For example: