Google Transit Feed Specification Data
Google's transit feed specification is well documented by Google's page on the subject.
Schedule data in GTFS format is available for download at http://developer.trimet.org/schedule/. You will find directories numbered according to the date the schedule takes effect:
<4 digit year><2 digit month><2 digit day>
TriMet schedules start on Sunday at 12:00 a.m. and generally are valid until the following Sunday at 12:00 a.m. Schedules are not always published each week, so a published schedule may remain valid for more than one week. Schedules usually are published no later than 6:00 p.m. on Saturday.