East 143rd Street Station, Port Morris Branch
The Port Morris Branch is an abandoned railroad trench that passes through the South Bronx and under St. Mary's Park.
The Port Morris Branch does not have a direct connection from the northbound NYCRR Line but instead passes under the NYCRR and travels parallel to it on the East up to the Oak Point railyard. Accordingly, there would need to be some kind of messy junction to connect subway trains coming in from Randall's Island to the Port Morris Branch headed northwest, while making it possible for freight traffic to continue north into the railyard.
The IRT Pelham Line (#6 train) arrives from the east under 138th Street, turning north at Bruckner Boulevard, crossing under the Port Morris Branch and continuing north under Southern Boulevard into a narrow trench. This would, obviously, be a desirable location for a direct transfer between lines. The Port Morris Line trench passes between buildings west of Southern Avenue. Building platforms and a station would require demolishing portions of these buildings including a very formidable-looking warehouse on the northwest corner of Southern Boulevard. The platforms (and, possibly, a surface level station) would need to extend into the sliver of land between Bruckner and Southern Boulevards. Then a pedestrian tunnel would need to run a north (and/or down) to reach the 143rd Street IRT platforms.
Con Ed has a large building in the triangle between Bruckner Boulevard, Southern Boulevard and 144th Street, just north of the Port Morris Branch. The facade facing Bruckner Boulevard tries to give the illusion of old rowhouses, but it's all a lie covering something electrical and modern.
The Port Morris Line winds its way diagonally across the street grid to the southeast corner of St. Mary's Park. The trench is flooded and/or overgrown and passes tightly between large warehouses along the entire path.
Next: St. Mary's Park The Bronx