[Busy Bee]

A Triboro subway scheme never really made much sense going up the New Haven Hell Gate Line to Co-Op City anyways, especially after the M-N ESA East Bronx line is put in place as it would kind of be a duplicative service, especially so if there is ever a M-N station in the southern Astoria area (in addition to the four planned for the East Bronx). A number of factors including the aforementioned constraints on the Hell Gate Bridge itself being 4-track and most of the Amtrak/M-N r.o.w. up to Pelham doesn't really have the space for 2 dedicated tracks for Amtrak, 2 dedicated tracks for Metro-North plus another 2 for a subway based service (plus the FRA might make them build a bunch of intrusion barriers whereas they will probably get a waver for the Bay Ridge branch due to low usage. A Triboro service sharing tracks with mainline Metro-North is a non-starter, no serious transport professional would advocate for such a thing which is why I always found the notion of a Triboro service crossing the Hell Gate so perplexing. Unless the Triboro rolling stock is built to mainline specs like M-N and LIRR, which it won't and makes little to no sense to do so, there isn't really a way to get it to the Bronx without a tunnel IMO. And once it's in the Bronx it would do a better job being a distribution type service by crossing East-West across the S. Bronx and the only way to do that is to get a tunnel from either Steinway across Randalls Island into Mott Haven where it can maneuver up the NY Connecting RR viaduct and sort of spiral into the Port Morris branch cut OR a tunnel from a station serving LGA and skipping to Rikers Island -->North Brother Island and diving right into the mouth of the Port Morris cut. Where it goes from there is chapter two of a much longer conversation.