Out with the Old, In with the New.
New York City Transit Authority (NYCTA) R120 locomotive no. 0L907 (Republic Locomotive Works, 1990-1991) is on the south end of a work train assisting with track replacement north of 36th Ave Station on the Astoria Line. This type of track replacement is known as a "panel job," and involves workers cutting out 39' panels of track, two work trains moving old panels out and new panels in, and two large cranes, typically from Bay Crane, moving panels between the street and the elevated structure.
Visible here is the old panel being carried by the crane car, and the new panel being placed by the crane that lifted it up from the street. A southbound N train is visible far up the line waiting until both cranes have set down their panels and it is safe to pass.