It's a picture of the Bowery "EL", Second and Third Street Lines. You'll have to click to enlarge it, it probably won't look like much if it's seen small. The picture below is a detail of the one above.
This together with a couple of the New York City ferry pictures by Cecil Bell (already posted, in the archive) are my favorite pictures of that city. Philadelphia used to have el trains complete with stations and tracks that look just like the ones on New York, and I used to look forward to riding them. The elevated stations were designed to resemble German railroad stations of the 19th century. Maybe Frank Furness, the famous Philadelphia architect and champion of railroad architecture designed some of these.
Furness believed in designing ordinary residences and business buildings to look like old railroad stations and modernists widely criticized him for it. I can't imagine why. German railroad stations are one of the most pleasing structures ever built by man and it makes no sense to confine their use to only one purpose.
I love the film noir slatted shadows cast on the street by the tracks and steel above. How often do you come across architecture that distinguishes itself by the fascinating shadows it casts? Walking up the steps and through the corridors of these elevated wood and steel cathedrals was a real treat and I for one miss it.