StopTimeUpdate stop/stop_sequence pairing must match GTFS?

[isabelle-dr]

Issue by barbeau October 20, 2017 Originally opened as https://github.com/CUTR-at-USF/gtfs-realtime-validator/issues/297

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Summary:

We currently have rule "E045 - GTFS-rt stop_time_update stop_sequence and stop_id do not match GTFS" for this, but after this discussion it doesn't look like this is explictlly mentioned in the spec - see: https://groups.google.com/forum/#!topic/gtfs-realtime/BZOfsVeI2Cc

And StopTimeUpdate docs: https://github.com/google/transit/blob/master/gtfs-realtime/spec/en/reference.md#message-stoptimeupdate

A point to clarify in the current spec, and potential part of a proposal to add trips with new geometries dynamically, or a proposal to identify child stops of stations.

Note that changes in stop_sequence would also affect VehiclePosition.current_stop_sequence: https://github.com/google/transit/blob/master/gtfs-realtime/spec/en/reference.md#message-vehicleposition

[isabelle-dr]

Comment by barbeau October 30, 2017

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More comments on a proposal regarding needing to better specify changes to trips, including changes to stop_sequence:

• https://github.com/google/transit/pull/81#issuecomment-340190869
• https://github.com/google/transit/pull/81#discussion_r143999532

[isabelle-dr]

Comment by barbeau Aug 06, 2018

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Also, it looks like Google and some producers are supporting changing stop_ids in the real-time feed to represent changing platforms at stations, when a platform assignment isn't known at static GTFS build time: https://groups.google.com/d/msg/gtfs-realtime/BZOfsVeI2Cc/gIUjGbkCBAAJ

In this case, changing from the parent station ID to the child stop ID is supported, which means that the stop sequence/ID pairing won't match GTFS by definition.

[isabelle-dr]

Comment by minhhpham Sept 29, 2018

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We performed an analysis using transit-feed-quality-calculator and found these agencies that have stop/stop_sequence mismatch:

Feed	Location
Cincinnati Metro Trip Updates	Cincinnati, OH, USA
HART Trip Updates	Tampa, FL, USA
Saskatoon Transit Trip Updates	Saskatoon, SK, Canada
LTD Trip Updates	Eugene, OR, USA
VIA Trip Updates	San Antonio, TX, USA
ETS Trip Updates	Edmonton, AB, Canada
MST Trip Updates	Monterey, CA, USA
MBTA Trip Updates	Boston, MA, USA

[isabelle-dr]

Comment by barbeau December 13, 2022

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Per the discussion of supporting real-time stop assignments in GTFS Realtime (see proposal PR google/transit#219), we agreed NOT to enforce stop/stop_sequence pairing matching in the GTFS Realtime spec. If this changes, it will be part of the GTFS Service Changes v3.1 spec. So our rule in the validator related to this needs to change.

[barbeau]

Given that stop/stop_sequence pairing is a common error in feeds, but as discussed above there are also cases used in practice that the spec is silent on, I propose we make this a warning instead of error.

Specifically, the community adopted an official experimental practice that should replace the undocumented practice of platform changes - see https://github.com/google/transit/pull/219. We should warn producers using the undocumented practice that they should switch to the official experimental method of platform changes. This should help increase adoption of the experimental method.