Trip updates
Also: gtfs realtime, gtfs-rt, realtime
GTFS Realtime’s running commentary: for each train out today, when it’s now expected at its remaining stops.
A GTFS timetable is the plan. GTFS Realtime is its live companion, and a trip update is the part that matters most: it names a trip from the timetable and gives new times for the stops it hasn’t reached yet.
Nothing is sent to you. You fetch the whole set, and it describes every train running at that moment. Fetch it again a little later and the times have moved.
Trainiac matches each trip update to the train it’s about, and shows its times as that train’s expected times.
In Trainiac
Expected times on a Bay Area journey that hasn’t finished.