Ad-hoc trips in GTFS-RT TripUpdates feed use of trip_id not found in GTFS-Static

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IT Supervisor for AC Transit working on new GTFS-Realtime feed.

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I am trying to tune a new GTFS-RT TripUpdates feed and would like to know which scenario is better for data consumers regarding adding trips not found in GTFS-Static:

1. Set a negative (fake) trip_id to a specific trip inside TripDescriptor. This negative (fake) trip_id is not found inside GTFS-Static but is provided for backwards compatibility for older data consumers which assume a trip_id exists.

2. Instead of providing a fake trip_id, it will be omitted. We assume a fake trip_id is not necessary for modern GTFS-RT data consumers.

Note that alongside the route_id, direction_id, start_time and start_date will be set. Note that the additional properties may or may not coincide with a specific trip inside GTFS-Static trips.txt