Page "New York City Subway chaining" Paragraph 17
from
Wikipedia
The local ( usually outside ) tracks on a given BMT / IND line are numbered 1 ( south ) and 2 ( north ).
The express tracks are numbered 3 ( south ) and 4 ( north ).
If there are an odd number of mainline tracks, the center track is ( for example ) track 3 / 4.
The signals heading southbound will show the location as track 3 and northbound track 4.
Additional tracks on the same chaining line are usually numbered higher by the same rules.
On the four track BMT Brighton Line, the tracks from west to east are:
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2.529 seconds.