Is there abandoned subway infrastructure out there that very few or no one knows exists?

[CenSin]

On 8/7/2023 at 1:02 AM, ABCDEFGJLMNQRSSSWZ said:

I have 3 theories:

1. The IRT started constructing the 4th Avenue line before the contract was officially awarded to the BMT, and BMT construction basically destroyed whatever IRT infrastructure that had been constructed.

2. The IRT constructed provisions for the 4th Avenue line alongside when the BMT building it's 4th Av subway. These provisions extended as far as Butler St, but have been sealed off and lost to time.

3. IRT started constructing the 4th Avenue line before the contract was awarded to BMT, but BMT preserved what IRT had constructed

Subway history: https://nycsubway.org/wiki/The_Dual_System_of_Rapid_Transit_(1912)

Quote

The Tri-Borough Plan. Early in 1908, the Commission adopted routes in Brooklyn which, with the Fourth Avenue, Brooklyn, Subway, it linked up with the Broadway-Lexington Avenue Subway by means of bridges and tunnels over and under the East River. The whole plan became known as the Tri-Borough System. In Brooklyn it embraced the Broadway-Lafayette Avenue Subway running from the end of the Williamsburg Bridge out Broadway, Brooklyn, to Lafayette Avenue and back through Lafayette Avenue to a junction with the Fourth Avenue Subway at Fulton Street, as well as two extensions of the Fourth Avenue Subway running to Ft. Hamilton and Coney Island. The estimated cost of this system was about $147,000,000 and the plans provided for about 45 miles of new road including both underground and elevated portions.

There are a lot of provisions in the form of station shells and bellmouthes all along the Eastern Parkway line.

Wikipedia: https://en.wikipedia.org/wiki/Nevins_Street_station

Quote

Between this merge and Atlantic Avenue is another unused trackway, splitting from the local track towards a subway under Fourth Avenue (later built as the BMT Fourth Avenue Line). This trackway and another trackway (both built for the same proposed subway) end at the same level, under Fourth Avenue, just west of the Pacific Street station on the current BMT Fourth Avenue Line and a few feet higher.

Have a look at the area marked 46c (source):

[ABCDEFGJLMNQRSSSWZ]

2 hours ago, CenSin said:

Subway history: https://nycsubway.org/wiki/The_Dual_System_of_Rapid_Transit_(1912)

There are a lot of provisions in the form of station shells and bellmouthes all along the Eastern Parkway line.

Wikipedia: https://en.wikipedia.org/wiki/Nevins_Street_station

Have a look at the area marked 46c (source):

Ye, ik there are currently bell mouth provisions on the Eastern Parkway line, but these photos are from a good ways down 4th Avenue. On the Vanshnookenraggen track map, there is no mention of anything IRT south of Eastern Parkway on 4th Avenue even though Historical Archives has the IRT taking photos of what appears to be some sort of underground infrastructure further south. That's why I wonder if there are abandoned IRT tunnels under 4th Avenue somewhere between Atlantic Av and Union St that have been completely lost to time.