In New York City, The New York Central crossed the Harlem River in two locations, Spuyten Duyvil on the West side Line where the Harlem River meets the Hudson River and at Park avenue. The park avenue crossing is interesting in that the present bridge is probably the 4th bridge built by the railroad in that location. It is a 4 track lift bridge constructed in 1954 replacing a4 track swing bridge which was built in the 1890s. The swing bridge replaced a draw bridge built earlier which replaced a trestle which was the original span across the river for the railroad.
Here is a newsclipping showing the construction of the present lift bridge located just west of the original swing bridge. Imagine that in 1954, the railroad made the switch to the new bridge with very little disruption in service.
Here is the Lift Bridge as it exists today, about 60 years and four railroads (NYC, PC, Amtrak and Metro North) later.
Over on the West side line is the Spuyten Duyvil Bridge. It is a swing Bridge design and its low to the water. Originally used for the West side freight line which we know as the High Line, the tracks and bridge are used today by Amtrak to route Empire service and Long distance services into New York's Penn station. Amtrak trains discontinued use of Grand central in the 1990's.
From Metro Norths spuyten Deyvil station.
Looking from the Harlem River side
And from the Hudson River side
The New york central was not the only railroad to cross the harlem River over a bridge. The Long Gone third ave and Ninth ave Els had spans and today. The Broadway No 1 train still crosses on a lift bridge. This bridge was replaced in the 1960's and was slipped in place of the old bridge with the removal and replacement being completed over a weekend.
The Harlem River Bridges can open for almost any kind of a boat shipment. Here we have the Replacement Willis ave vehicle bridge making its way to its new home. I think this is probably a most unusual river movement. We have a Bridge crossing under a Bridge.