Ben
That photo is a puzzler. I looked at it again. Two things to consider in locating the photo. It appears to be construction associated with the Dual contracts and the structure looks like its at a pont where there is a station but not with a center platform. I would say its about 1915 or so in time, about 20 years earlier than the photos you posted later. The second point is that this construction was not in a street but on private right of way and there is no existing rail line in the street that one can see. The buildings in the backround suggest it is near downtown. The Culver line in the vicinity of 36th street ran on private right of way over towards Ditmas Avenue. If its marked 4th avenue, the location doesn't seem right. Did the 3rd ave extension of the 5th ave el have any non center platforms?
