Question regarding trip_id's and frequencies.txt :
There is a case of multiple off-peak and on-peak time periods for a route with corresponding frequencies. To illustrate:
6am to 8am : off-peak
8am to 10am: on-peak
10am to 6pm: off-peak
6pm to 8pm: on-peak
8pm to 12am: off-peak
Why I'm asking this :
Everything else is the same! Having to use multiple trip_id's for on and off peak periods leads to having to provision that many multiples of rows in stop_times when the sequence of stops is the same and we're using the same arrival/departure time values (starting from 00:00:00) merely to tell time offsets between stops. We're having many peak/off-peak periods and the complication coming from having to use multiple trip_id's makes it relatively more economical to simply run some calculations, determine individual trips, and do things the traditional way. As it is there is redundancy owing to there being different frequency values for weekdays, saturdays and sundays.
It's not mentioned that trip_id needs to be unique over there. But it's also not mentioned that we can use the same trip_id values for different time blocks.