Discrepancies in service start_dates in archived GTFS feeds

[idr...@gmail.com]

Hello,

I am working on an analysis of service levels based on the T's historical GTFS feeds and I'm running across some issues relating to service dates that I could use some help interpreting. Let me start with an example of the end product, for the 24 bus:

You'll notice the two gaps in (roughly) May and then July-Aug that I don't believe correspond to actual suspensions of service. I have a copy of every GTFS feed that covers these periods, and in e.g. the one for 2020-05-04 I find that the 24 is scheduled to make 58 daily trips on the SpringWeekday schedule. So far so good. But when I cross-reference that schedule in calendar.txt I find the following:

SpringWeekday,1,1,1,1,1,0,0,20200615,20200619

In other words, the spring schedule begins on 6/15 and ends a few days later on 6/19, accounting for a big gap, followed by a brief peak, in the service levels chart. There is a similar issue where the SummerWeekday service has this entry in some later feeds:

SummerWeekday,1,1,1,1,1,0,0,20200817,20200828

...and since all of the 24's scheduled trips are on this service, they are not accounted for at all until 8/17, causing the second big gap in the chart above.

How should I interpret this? Is it possible there was an error in these service dates that I could correct by hand in my code? I'd be super appreciative of any tips, pointers, or corrections here.

Best,

Ian Reynolds

[Developer]

Hello Ian,

I looked into it and there's not really an error in the data.

It really is the case that the 24 did not run during that time, and in fact the incorrect part is indicating service 6/15 - 6/19​. However, if you look at a GTFS feed closer to that time (e.g., the first Summer feed, 20200605.zip), you'll see that we do not have trips scheduled during 6/15 - 6/19 anymore. We try to update the feed as often as we can, but particularly around rating changes there are a lot of moving parts and the static data more than a week or two out can be incorrect. One thing you could do is look at the data in a feed only for the dates up to the next feed. We try to never change things retroactively, so that should be the best source of what the static data is on a given day. We publish updates frequently related to planned shuttles and other service changes.

Another thing to note, depending on the purpose of your analysis, is that a related route, the combined 24/27 (route_id: 2427) did run during that time. What might be useful for you is looking at our experimental feed data for lines which group related routes. For example, in the 2020-05-04 feed that you mention, you'll see that the 24 is part of a "line" consisting of the 24, 24/27, 27, 33, and 32/33 routes, which share a basic trunk and serve a similar area and similar stops.

Best,

Developer@MBTA

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Sent: Monday, March 29, 2021 5:50 PM
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Subject: [massdotdev] Discrepancies in service start_dates in archived GTFS feeds

 

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[idr...@gmail.com]

Super super helpful, thank you!

- Ian