GTFS and GTFS RT Extensions

Interesting extensions to GTFS by Agency:

Extensive use of the "pathways" spec for elevators/accessible entrances
- Includes "pathway_code" to interface with the elevator outage feed
- "elevator_id" extension in GTFS-RT for alerts which are elevators
"track" as extra column in stop_times.txt (with accompanying GTFS-RT extension)
"tripHeadsign" and "stopHeadsign" in GTFS-RT for "ADDED" trips. May need to add more trip attributes
"departureBuffer" in stop_times.txt to model vehicles which may leave earlier than their scheduled times (This did not end up getting used.)
Proposed "notes" spec to be able to add scheduled notes e.g. "This train will depart when the Yankees game ends."
Using a format very similar to transfers.txt but with feed identifiers to specify cross-feed transfers (e.g. NJT Penn Station to LIRR Penn Station). This lives in a control file outside GTFS.
"DELAYED" current_stop_status in GTFS-RT, which is used by MNR. We may also add "HELD," which means something slightly different for them.
Peak/offpeak flag in trips.txt ("peak_offpeak")
We are using "stop_headsign" to mean the sign in the station that you follow at that stop, e.g. "Downtown/Brooklyn".

Cross-feed fares - specify e.g. "There are free transfers between the Staten Island Ferry and a few subway stops in lower Manhattan."
Contextual alerts - some alerts should only appear on trip plans under certain circumstances, for example if you are taking a LIRR train from Long Island to Penn, then transferring to a NJT train to the Meadowlands, you may be eligible for a special fare.
Alert source - for GTFS-RT alerts, specify in data whether the alert is an elevator alert / escalator alert / delay / detour / etc.
Canonical stops/shapes - specify the "marketing" list of stops and shape for a route. This is similar to Dave Barker's "route variants" proposal
Internal MTA STIF format tracks non-revenue service; looking to add this to GTFS someday
real-time depot pull-in/pull-out API - possible standardization?

Sound Transit contracts out all service via multiple agencies, making for multiple feeds that report as the agency "Sound Transit". Makes a consolidated GTFS difficult and breaks many conventions about having an agency unique to a feed. Currently handled operationally, but hints at the need for GTFS meta-data that details how feeds link together.