Subway GTFS Stop Dwell Times

[Stephen Bauman]

I'm using the GTFS data for analysis purposes. One problem is that station dwell times are not included (in the stop_times table arrival_time usually equals departure_time). Nominal station dwell times are 30 seconds. 

How did the MTA account for station dwell times? Did they add the nominal station dwell time to the travel time to the next station?  N.B. I calculate travel time to next station as: next station arrival_time  minus current station departure_time.

I also noticed that the next station travel time varies during the day. I assume any deviation from the minimum travel time between the two stations is due to "congestion". I assume this congestion to be a leader not having cleared the next stop before the follower would have arrived at the next stop within the minimum travel time.  Is this a reasonable assumption of the MTA's workaround?

Thanks in advance for a quick reply.

Steve