This is a train of SIRT cars at the Ditmas Avenue station of the Culver elevated in Brooklyn.
After 1954, when the Culver El was cut over to connect with IND at Church Avenue the BMT Culver-4th Ave trains terminated at a single outboard track at Ditmas Avenue. An equipment shortage led to the use of a number of SIRT cars on this line as they were very similar to BMT Standards in size and functionality, though the two types couldn't MU together.
Eventually the remnant of the BMT Culver operation was trimmed back to a shuttle between 9th Ave and 39th St and Ditmas -- later it became a single-track, single-train shuttle operated by IRT Lo-V's with extensions at the doors to compensate for their lesser width. The segment from Ditmas to 9th Ave has been demolished now.
Photo courtesy the Joe Testagrose collection