David Bennetts wrote:

I was intrigued when visiting New York a couple of years back with the "gap
filler" arrangements at South Ferry subway station, which was on an
extremely sharp curve and could only handle the front half of a train. I
believe the station has just been rebuilt to eliminate this curve. See
http://www.nycsubway.org/perl/stations?6:2678

It has not been rebuilt. Rather, a new two-track terminal station has
been built essentially underneath it. The new station has not yet
opened, but when it does open, the old station will be decommissioned.

The old trackage will still be used, as it provides a valuable track
connection between the West Side IRT (1/2/3) and East Side IRT (4/5/6).
It also has an inner loop track, which only connects to the East Side
and is used to turn East Side trains that terminate at Bowling Green
(mostly off-peak 5 trains). The inner loop has its own platform, which
was used until the 70's by a shuttle train to Bowling Green.

Gap fillers remain in use at Union Square (southbound 4/5/6 platform)
and at Times Square (shuttle). And there will still be one station that
can only accommodate half of a train: 145 St on the 3.
--
David of Broadway
New York, NY, USA