This is likely a study of the rolling lift bridge that connected South Station to the Old Colony mainline.

The construction of South Station in 1896-98, involved the rerouting of several of the old lines from the west and south. The New York, New Haven & Hartford Railroad constructed a six-track rolling-lift bridge, the first of a new class of bascule lift bridges invented by William Scherzer (1858-93). The bridge was the fourth to be built by the Scherzer Rolling Lift Bridge Company, and the first to be constructed outside of Chicago. The six track bridge is made up of three separate through riveted truss spans. Each draw span, weighing approximately 500 tons, could be raised or lowered independently of the other two, requiring usually thirty seconds to either open or close.