These files contain historical information about the movements of trains on 
MTA New York City Transit's "A Division" subway network.  Specifically, trains in
revenue service on the (1) through (6) lines as tracked by the Automatic Train Supervision system,
referred to as "ATS."

The data is presented in a Comma Separated Values (CSV) format, with one file for each
"service date."  Each row of a given file represents a particular "train event" -- the arrival
or departure of a particular train at a particular station.

The list below describes the columns of these CSV files.  As much as possible,
the values in these files correspond to values in the published GTFS schedules.
The list is followed by some additional caveats about the information.

COLUMNS:

service_date: The date of service.  Generally, a train trip is associated with a given service
date if the trip starts during that date, even if some of the trip happens on other dates.

train_id: the alphanumeric identifier of a particular train trip in the ATS system.  These repeat across 
days, so the real unique key for a specific train trip is (service_date, train_id).  At this point, these values
*do not* correspond to values in the published GTFS files.

direction_id: corresponds to the directions in published GTFS files.  1 = S(outh), 2 = N(orth).

timestamp: the (calendar) date and time of the event

event_type: 1 = arrival, 2 = departure

route_id: corresponds to the route_id in published GTFS, with the exception that express trains
do not have the suffix 'X'

stop_id: the GTFS stop_id of the station at which the event is happening.

track_id: the identifier of the track on which the event his happening.  Generally, tracks are 
named according to the following convention, regarding the last digit/character of the track ID:

"1" = southbound local
"2" = southbound express
"3" = northbound express
"4" = northbound local
"M" = middle track (reversible track for express service in peak direction)

CAVEATS:

There are many curiosities that users will discover about this data.  They result primarily 
from the realities encountered in day-to-day subway operations, including incidents, delays, etc.  
They are also a function of the particular type of technology used to identify, track, route, 
and dispatch trains on this portion of the subway network.  

One thing to be particularly aware of is that the ATS system does not yet cover the (2) and (5) lines 
north of 149th St in the Bronx.  It is in the process of being extended, both for train dispatching and
control purposes, as well as to feed data to the PA/CIS arrival signs and announcement system.  As such,
there will not be reliable data for the (2) and (5) lines north of 149th St.