Serious NYC subway geekery alert. Who cares about the undersides of two different elevated trains?
So what if one has three tracks (and always did), while another line had four, but now one is empty?
Elevated at Gunhill Road
Looking up at the elevated section of the #5 train at Gun Hill Road, you see three pairs of stringers, with three pairs of tracks sitting directly on top them. That’s the standard for NYC’s elevated lines: one uptown track, one downtown track, and a “hot” track in the middle, for express trains in either direction.
6 train overpass
But look at this, an overpass of the #6 train, at Allerton Avenue, obviously four pair of stringers, but one of them has had its track ripped out. This line was originally part of the grandiosely-named New York, Westchester, & Boston Railroad (NYWB), a short-lived venture that once carried commuters between Westchester and the Bronx. The NYWB had four tracks: two running each way. After it went defunct, the NYC MTA took over the line, and converted it for the #6 train, which had to operate on a 3-track system, like the rest of the MTA’s elevated. Actually, all the converted NYWB track is surface; this is only an overpasss.
Other differences: Note that the tracks do not sit right over the stringers. Also notice the much heavier construction of the NYWB’s overpass compared to the elevated at Gun Hill Road.