we are consumers of the TfL Tube Arrivals service. We are using the TfL Unified API, primarily the Streaming (SignalR API) version with the Polling (HTTP polling API) version as a backup.
Based on a user report, it appears that there are missing arrival predictions for Northern line trains, in particular departing from High Barnet, after approximately 23:10 a few days ago on Sunday 2020-03-01.
Specifically, we have recorded these two train departures from High Barnet:
- Train 117 departed HB at approximately 23:05, headsign Morden via CX,
- Train 137 departed HB at approximately 23:09, headsign Morden via Bank
However, after triple-checking both our application logs, as well as the incoming raw SignalR Stream feed messages, we have been unable to find any further departures (other than the above two trains), or other southbound train movements, for Northern line trains from High Barnet.
Additionally, we have been unable to see any train departures after 23:11, or other southbound train movements, for Northern line trains, from Edgware other than the below trains:
- Train 016 departed Edgware at approximately 23:03, headsign Morden via CX,
- Train 045 departed Edgware at approximately 23:07, headsign Morden via Bank,
- Train 046 departed Edgware at approximately 23:11, headsign Morden via CX
On the other hand, northbound trains (e.g. from Morden, from Kennington, etc.) seemed to have been tracked fine, including departures and ongoing trains.
Note that when I say “train departure”, due to how the Arrivals feed works, I simply mean the first sent message for that train’s just-started trip; this can either be sent as the train is leaving the station, or as it’s already on the way to the second, or even the third station; we have found no messages of any kind for these trains which presumably were running in reality.
Our user reported that they have been on a train from High Barnet to East Finchley, that departed High Barnet at approximately 23:30, which is in line with this scheduled trip:
Similarly, we can see that the only scheduled trains going to for example Kennington are trains that depart at 23:04 and 23:08, corresponding to the two trains we have tracked starts of mentioned above (trains 117 and 137).
Can anyone correlate the above findings? If so, is this perhaps a bug in the Tube Arrivals system that maybe doesn’t send predictions for trains going from High Barnet to East Finchley, or something like that?
We have noticed that at the time in question, Citymapper had real time train predictions for numerous trains going in that direction, e.g. at 23:39 from Finchley Central to East Finchley there were train departures “Due”, “Due” (apparent duplicate?), “5 min”, “9 min”, and “23:55”; other than the 23:55 time, the other times were marked with the “real time” icon, suggesting they were tracked by a real time feed.
Is there perhaps a third feed that we are unaware of, other than the above mentioned SignalR API feed and HTTP polling API?