Use of "activity" field flags for GTFS pickup/dropoff

[planarnetwork]

Use of "activity" field flags for GTFS pickup/dropoff

[mk-fg]

Two more quick notes:

• Sometimes these flags can be somewhat overlapping, e.g. "TFT -U" with both TF and T in there for "-U" stops where trains attach to each other.

• "-U"/"-D" flags on stops can be used as a sanity-check for associations, as - from a quick glance - these seem to line up between cif schedule/association datasets, which might also be the reason why there're always matching schedules for association records (to have these flags updated).

[mk-fg]

One other interesting case can be stops with "N - stop not advertised" flag.
There are public times set for some of these, but they should probably be marked as "no stop" in GTFS regardless, causing a minor mismatch with current algo.

More discussion about this particular flag can be found here:
https://groups.google.com/forum/#!searchin/openraildata-talk/cif$20activity/openraildata-talk/eBTiB1BxrRw/diefBX9hiQYJ