There's only three places in the NYC subway system where a loop track enables turnaround: 1. The original City Hall Station on the East Side Interboro where the local trains turn around; 2. The inner loop at the original Soituh Ferry terminal where some 5 trains turn around; and 3. The outer loop at the original South Ferry terminal where 1 trains used to trun around and is now used only for car storage and non-revenue moves.
ALL other terminal stops rely on the trains being double ended and they change ends in conjunction with one or more cross overs to get over to the correct track.