Proposal: exact_times

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Brian Ferris

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Aug 30, 2011, 7:54:50 AM8/30/11
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Original Discussion:

http://groups.google.com/group/gtfs-changes/browse_frm/thread/e6ef325c1ae92b6c

Summary of proposal:

The addition to the frequencies.txt section of the GTFS spec:

exact_times (optional):
The exact_times field determines if frequency-based trips should be
exactly scheduled based on the specified headway information. Valid
values for this field are:
“0” or (empty) - Frequency-based trips are not exactly scheduled.
This is the default behavior.
“1” - Frequency-based trips are exactly scheduled. For a
frequencies.txt row, trips are scheduled starting with trip start time
= start_time + x * headway_secs for all x in (0, 1, 2, ...) where trip
start time < end_time.

The value of exact_times must be the same for all frequencies.txt rows
with the same trip_id. If exact_times is 1 and a frequencies.txt row
has a start_time equal to end_time, no trip must be scheduled. When
exact_times is 1, care must be taken to choose an end_time value that
is greater than the last desired trip start time but less than the
last desired trip start time + headway_secs.

Initial implementation from a GTFS producer and consumer:

Producers: Over 6% of the feeds in the current Google Transit corpus
define an exact_times field.
Consumers: The field is validated in the googletransit extension of
the feed validator and used in the Google Transit product.
Status: Prime candidate for acceptance.

Unless there are objections in the next week (Sept 6), we will
formally add this proposal to the GTFS spec.

Thanks,
Brian

Brian Ferris

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Sep 6, 2011, 2:49:34 AM9/6/11
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Seeing no objections, I'm making this one official.

Brian

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