Local transit historian and railfan Dj Hammers makes tons of great videos showing how subway transit works and runs in the City.
In this short video captured at the Lexington Avenue - 63rd St station, watch as test trains get sent down the nearly finished 2nd Avenue Subway tracks.
I came across some test trains passing Lexington Avenue - 63rd St to test the third rail, signals, and track on the newly-built Second Avenue Subway! Luckily, I could see these trains from the public area of the Lexington Ave - 63rd St station from the staircases between the two levels of the station. Very interesting operation!
via Dj Hammers