The 4th avenue line construction started in 1915 It was actually the Municipal Railway corporation in partners with the City of New York. It was a subsidiary of the BRT . The 1970's construction was basically to extend the platforms to handle 10 car trains and the newer 75 foot cars of 8 at the time.
There are a few spots you can still see the old
45 St still has the round poles in spots and 9th street still has the old tile work in the culver corridor
The most interesting station is 36 street It only has exit stairs on one end The reason for this is that the original plan for the station was changed The station was built with future connections for a 40 street connection to the West End and Culver When that connection was made the station moved north by about 300 feet to accomadate the West End connection as it is today. If you look south of the station the tile work extends to past the point of the West end. The three original tunnel entrances for the 40 street connection are still there The is one on track 2 going northbound. There is a deep one in between tracks 2 and 4 ending at the West end portal and there is one in between tracks 1 and 3 going southbound If you ever went local going southbound the train does a curve to the right as you leave 36 st Thats to get around the downgrade for the 40 st connection
Its a little hard to see but this is looking at the deep entrance from 40 st in between tracks 2 and 4
