Per stop predictions - scheduled times may be shown if a GTFS-rt producer aggressively drops predictions

[barbeau]

We're seeing this issue when testing in Tampa with a GTFS-rt feed with multiple StopTimeUpdates per trip. The GTFS-rt producer is very aggressive in dropping StopTimeUpdates - as soon as the vehicle passes the stop, the StopTimeUpdate disappears from the GTFS-rt feed.

The resulting UX is that the user sees real-time info as the bus approaches the stop, but then it flashes to scheduled time just as the bus arrives/departs (e.g., it shows negative scheduled arrivals).

We’re working on a patch that would fix the scenario for late/on time arrivals – the resulting behavior with the patch is that negative scheduled times would never be shown if EDIT <property name="showNegativeScheduledArrivals" value="false" /> is set in data-sources.xml for an agency.

The WIP PR for this issue is #160.

However, the early arrivals are a problem – with the GTFS-rt feed is currently dropping early arrivals before the bus is scheduled to have passed the stop – the end result is that we show real-time info until the bus passes the stop, but then the ETA bounces back up to the scheduled time and we count down the scheduled ETA until the scheduled time is past. There’s no way to fix this on the consumer end without violating the GTFS-rt spec, so we’re trying to get the GTFS-rt language clarified for the producer requirements.

I've opened a GTFS-rt proposal to clarify this language, and require producers to keep predictions in the feed until after the scheduled arrival time for that stop (from GTFS stop_times.txt) has passed.

If you're so inclinded, please vote for this GTFS-rt proposal at google/transit#16.

cc @sheldonabrown @cagryInside

[cagryInside]

@barbeau The following property name should be showNegativeScheduledArrivals. I fixed that in the PR.

We’re working on a patch that would fix the scenario for late/on time arrivals – the resulting behavior with the patch is that negative scheduled times would never be shown if property name="showNegativeArrivals"value="false" /> is set in data-sources.xml for an agency.

[barbeau]

Thanks! Copy and paste error on my part :). I just edited to fix it.