proposal: allow interpolated times to be specified in the feed

[Joe Hughes]

Summary:
Add a "timepoint" field so that feed publishers can specify
interpolated (non-timepoint) times.

Motivation:
In the GTFS, the entries in stop_times.txt either have a time
associated with them, which makes them timepoints, or no associated
time, which means that the application using the feed needs to create
interpolated times for that stop on that trip. However, agencies
often have local information that they can use to provide better
interpolations. Adding a way to distinguish timepoint times from
interpolated times would allow them to provide these interpolations in
their feeds.

If an application knows that a time is interpolated, it can pass on
that information to the user--this Google Maps query shows
interpolated times in Manchester:
http://tinyurl.com/24r6o3

Trip planning applications could also schedule transfers near
interpolated stops with a wider margin of error.

Proposal:
in stop_times.txt:
timepoint: Optional. The value should be either "0" or "1". If no
value is given, a default value of "1" is used. "1" indicates that
the stop is a timepoint on this trip. "0" indicates that the stop is
not a timepoint, so any times specified in the arrival_time and/or
departure_time fields for this entry should be considered approximate.

Testing:
A similar field is used internally in Google Transit, as can be seen
from the Manchester example above, and a few agencies are providing
feeds with this information.

Joe Hughes
Google Transit

[Devin Braun]

I can provide the San Diego feed including this new column if
requested.

Devin Braun
San Diego MTS

[Joe Hughes]

Thanks Devin, every bit of test data helps. If it's easiest, you can
just add it to your existing feed; new columns should just be ignored
by existing feed parsers.

Joe Hughes
Google Transit