Why was the Nostrand Ave station built on 2 levels, upper for express and lower for local? All the other express stops are island style platforms. Was there a lack of space above the cut?
I believe the street in that area was too narrow to go with four tracks across plus a mezzanine.
I believe that station and 86th in Manhattan on the 4/5/6 are the only express stations that don't have a crossover or crossunder.