Footnote: Door closing times by equipment type

A nontrivial component of dwell time is how quickly the train's doors open and close.  This is why double-leaf doors are common on most types of equipment you see...doors can be moved out of the way faster when they only have to clear half of the door area.  This is still fairly ubiquitous on metro and light rail systems, and is still somewhat common on mainline rail systems (except, for some reason, the LIRR and Metro-North since the 1990's).

The doors on the MTA's newer railcars tend to take much longer to open and close than their more senior counterparts, and that can have a notable impact on dwell times.  The figures below represent typical overall door closing sequence times (from the time the conductor pushes the door close button/the first alarm bell sounds, to the time the door is completely closed and the train can depart):

• C-3 cars: 4.8 seconds
• M-3 cars: 3.8 seconds
• M-7 cars: 8.9 seconds
• M-8 cars: 6.7 seconds
• M-9 cars: 9.0 seconds

The door closing time is markedly longer on the M-7 cars when compared to older fleets (8.9 seconds on the M-7 cars is nearly double how long it takes to close the doors on the M-3 cars, and even longer than the C-3 cars, which are only a few years older.  Metro-North improved upon this issue slightly with the M-8 cars, which land someplace in the middle between the M-3's and M-7's, but the MTA seems to have regressed with the new but troubled M-9 cars, which have a door closing sequence time that's a fraction of a second longer than the M-7's...

The newer cars, starting with the M-7's, have a positive lock feature where the doors close (to the point where they appear closed), then there is a split second before the door is lurched a tiny bit further, locking into place.  That second locking motion can't happen if there's some sort of obstruction in the way, so the design is, in theory, safer and less prone to the risk of dragging.

A 4.1 second difference may not sound like a big deal, but seconds add up very quickly...  An additional 4 seconds per stop on a 15-stop Babylon local train accumulates to over a minute of extra running time over the course of the trip, strictly from closing the doors.