GTFS -- Continued implementation problems with Frequencies.txt
Transit001
This is a follow-up to the past threads:
http://groups.google.com/group/googletransit/browse_thread/thread/1da8a2a2692f9e23/aed6edc3ae5e382d?lnk=gst&q=problem+with+frequencies#aed6edc3ae5e382d
and
http://groups.google.com/group/googletransit/browse_thread/thread/85dc61d73d7ac60a/ac373281e6bb3045?lnk=gst&q=problem+with+frequencies#ac373281e6bb3045
.
In the present state of Google Maps, whenever the Frequencies.txt
table is used in a GTFS feed, transit trips are still only displayed
with the interval time and duration time, whereas the absolute time
bounds as well as the user's search for "depart at" / "arrive by" time
are still completely ignored by the system. This causes the same trip
results to misleadingly be returned no matter what time the user
specifies in their search. This seems to be an ongoing shortcoming in
the implementation of GTFS feeds by Google.
This can be observed by the behavior of "Demo Transit Agency". For
example, please go to Google Maps, go to "Get Directions", and search
for a route between the following locations (specified in lat/long
coordinates) using the "public transit" option:
Source: 36.916428,-116.77175
Destination: 36.902617,-116.759477
The results show a trip with bus "40" (whose primary key is "CITY")
going from the stop whose primary key is "NADAV" to the stop whose
primary key is "EMSI". The results say "Service runs every 30
minutes" and that the duration of the bus trip is "12 mins". Both are
consistent with the data in the feed: the value of "headway_secs" (in
the Frequencies table) is 1800 which is 30 minutes, and the relative
time (in the Stop_times table) for "NADAV" departure is 6:14, and the
relative time for "EMSI" arrival is 6:26, which is a difference of 12
minutes (assuming one time is inclusive and the other is exclusive).
However, if I enter "2:00 a.m." for either the "Depart at" or "Arrive
by" options and re-do the search, the same results come up, even
though according to the data in the Frequencies table, the route is
not supposed to be in effect around 2:00 a.m. This indicates that the
"start_time" and "end_time" fields in the Frequencies table are
ignored by the system.
This would be misleading to users searching for transit routes of
agencies using the Frequencies table, because they would be given the
same route even if it was not in service at the time they were
searching for.
Is this somehow the intended behavior for the Frequencies table? Are
users supposed to just know that the results they are seeing may not
be true for the time they are searching? I can't imagine this being
the case because the GTFS specification specifically says that the
"start_time" and "end_time" fields indicate "the time at which service
begins with the specified frequency" and "the time at which service
changes to a different frequency (or ceases) at the first stop in the
trip", respectively. Am I correct about this functionality simply not
having been fully implemented?
As I understand, the workaround for this is to abandon use of the
Frequencies table (even if is applicable to the transit schedule in
question), and generate a static list of stop times. Is this what
feed developers are expected to do at the current time?
Note (for reference): The data for "Demo Transit Agency" is at:
http://spreadsheets.google.com/pub?key=puMHBiWYEbXT0UxQGLDpuBA&gid=10
. Other formats are linked from
http://code.google.com/transit/spec/transit_feed_specification.html#transitAgencyExample
(but do not use the data in the "Sample Data" section on that page).
Thanks for any assistance.