I went through all the old maps and images on this string. The Editor posted on 6/28/2006 a map called "Local Car Lines, Hackensack 1900-1938", and it shows parallel rail/trolley lines between Union and State Streets. As one looks east from mid-way between Union and State Street, the lines part slightly, one of them (evidently a trolley line) veers off to the right in order to link up with the end of Mercer Street.
That trolley line junction is exactly what the last picture posted by BLeafe depicts. The image caption is correct, it is looking east towards State and Mercer. This is pretty definitive. It would help to go back and look at that map posted in 2006. This is good historic image for the archive records, for part of the block bounded by the Railroad, State Street, Trinity Place, and Union Street.
I also agree that there was a trolley yard on the east side of River Street between the Susquehanna and Midtown Bridge approach, and some of the other photos on this string accurately depict that trolley yard. Nice work, guys.
Keep these tricky images coming, between all of us we can figure most of them out.