found this shot of the P&NJ bridge over the Delaware river south of state rt 90 just out side of philly, my question is this bridge still there and why is there a lift span and a swing span back to back ?
jim

Being an ex-Philadelphian, I do recall the bridge spans, but it would appear the span are still there. There is still plenty of rail traffic in the Philadelphia area. Route 90 crosses the Delaware in Northeast Philly on the Betsy Ross Bridge and puts you in New Jersey between Pennsauken and Palmyra. I seem to remember the Betsy Ross was built to replace a ferry in the mid fifties. Your bridge spans are just to the south of that, as can be seen in this Google Satellite Map ...

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The sizes of the two spans i question is very apparent in this overhead. (The shadows are quite helpful.) The traffic on the Delaware in the Philadelphia area is often quite heavy, and the sizes of commercial craft plying the river can vary greatly. I'm going to guess that width and height of the vessel might have something to do with it ... and two vessels can move past the spans in opposing directions at the same time.

Just guesses, Jim, but I do know that the rivers there are heavily travelled and that might have something to do with it.