In the 70's in NJ, there were still tracks in the sidewalk from the North Jersey Rapid transit in Hohokus at one spot(I saw another post that they still may be there today). Also, in Waldwick, in the E-L yards near the wye where they used to turn around the E-8's, there were a few tall cement pylons where ths line was elevated over the Erie tracks. I hung out at the WC tower occasionally back then (at 16) and there were some good guys there, the only names I remember were Dave Kinner and "Ace", they let me pull the switches in the tower a few times. At the Waldwick station, there was another good guy (Jim, I think), a stocky dark-haired guy, and since my mom used to commute to Paterson on the E-L almost daily, we got to be on familiar terms, and he let me climb up into the attic and retrieve some really dusty old stuff, including passenger ticket sales logbooks and a bunch of cardboard freight waybills from around 1912. I still have about 20-30 of these today.
I also spent a brief time in Boston around '77-79 and the A Watertown line seemed perfectly intact. I was always hoping they'd revive it, but I guess that was never to be.