[Update to fix the attachment problem]
This is to relate info about railroading in the town I grew up in, specifically, about a movable RR bridge over an inconsequential estuary that forms the Northern border of this Southern New Jersey town.
Paulsboro sits on the Eastern bank of the Delaware River, about 14 miles South of Philadelphia, in Gloucester County. That region of the state is riddled with tidal swamps and estuaries that flow westward into the Delaware from springs and other water table sources more to the East of the region. Most of Southern New Jersey was, when I was younger there, agricultural land, with a major frozen produce processing center in Bridgeton (Seabrook Farms). But along the Delaware coast, Gloucester and Salem counties proved to be able to provide excellent shipping port resources, feeding into Delaware Bay and ultimately, the Atlantic. Thus, captains of energy and chemistry established large refining and chemical production plants along the coast. Furthermost South, the Dupont Corporation built one of its principal chemical production and R&D sites at Pennsgrove (called "Chambers, Works" - it had it's own on-site narrow gauge rail hauling system). North of Paulsboro, in Westville, Texaco operated its "Eagle Point" refinery. And in Paulsboro itself there operated the "Socony Mobile-Vacuum" (as we called it), a huge refinery owned by Mobil Oil.
Now the rail system in South Jersey, in the early and mid 20th century, provided a prolific set of routes, serving both passengers and freight. The backbone of these lines were the routes to the Jersey shore resorts from Philadelphia and New York. Early in the century, two major railroads competed for fares to the shore - the Pennsy and the Reading - and, they both had their own right-of-ways, the Pennsy taking a Northern route heading Southeast to Atlantic City, with a branch-off at Winslow Jct. for resorts further South (Ocean City, Wildwood, Cape May).
The Reading terminus for its shore traffic was in Camden NJ (directly across the river from Philadelphia) and it used a parallel right-of-way to the South of the Pennsy that ran through Clementon before reaching its shore destinations. The Reading had also acquired the many small trunk lines serving the agricultural southern counties. Ultimately, these two companies combined to form the Pennsylvania Reading Seashore Lines RR (PRSL), which took over all the lines in southern New Jersey in the 1930's. A major branch of the PRSL serviced the southwest coast of the state, serving the industries and ports along the Delaware River and Bay.
And, while many of the bifurcations of the PRSL in Gloucester, Salem, Cumberland, and Cape May counties were ultimately abondoned, the Pennsgrove branch, the one that runs through Paulsboro and serves the ports and industries, has remained profitable and is now a part of the Conrail octopus.
But, that line has been around for a long time (Paulsboro once had a passenger station, and its Delaware river front was once a tourist destination), and the builders of the railroad needed to do something about that inconsequential creek that bounded the town on its Northern border - the Mantua Creek. It seems there was a need - a small one - but still, a need to allow boat traffic to navigate the Mantua.
And so was built the Paulsboro Moveable Bridge for the railroad. There are conflicting accounts as to the age of this wonder. One account puts it into the late 19th century, while another dates it to 1917.
It is an A-frame deck-girder swing bridge, originally manually operated, but automated for remote operation some time in the last decade or two. Here is a pic of it:
(In the pic, the bridge is in the "open" position - open for boat traffic).
Some time last year, there was an incident caused by structural failure of the bridge. A crossing train derailed and several freight cars tore up the rails for several yards along the right-of-way South of the bridge in Paulsboro. Inspections revealed a partial collapse of the bridge deck. One of the stringers (attached to the top of the "A" - you can see them in the photo) had also snapped. The newspapers speculated that the old stringers had fatigued and had given way when the train crossed.
But I knew better. I knew the cause right off, having an understanding of the engineering principles behind the bridge: it was compromise of the abutment support function. You see, that A-frame and those stringer cables do not support the weight of a train when the bridge is "closed" (closed for boat traffic, open for rail traffic). In that position, the "deck" (the part that can swing open) rests on the abutments so that the bridge functions in that position as a simple deck girder bridge, with girders supported at both ends by pilings or whatever. The A-frame and stringer cables are only called upon to support the deck when it is in the "open for boats" position. The stringer cable snapped when the abutment gave way somewhat and the weight of the train caused a shifting of the deck in its closed position, putting too much stress on those cables. I've learned through a friend who lives in Paulsboro, that the bridge was repaired (not replaced - whew!), and so, its simple, elegant design that has allowed it to work for a century (or maybe more than a century), marches on.
Many years ago, when I was doing some modeling, I wanted to try to model it and perhaps develop plans for a Model Railroader article on modeling the bridge. Unfortunately, that never came about. And I no longer live in Paulsboro.
But , perhaps, some master modeler who visits this site might try their hand at it. I'm not an engineer, and I haven't the slightest idea where one could find blueprints, but I can give you one design hint: that "A" frame structure does not stride the tracks at a 90 degree angle, but rather sits on a vector that bisects the rails at about a 15 to 25 degree offset (from 90 degrees), with the "furtherest away" leg on the right side of the rails (in the photo). Also notice that the "A" is asymmetrical.
Anyway, this is a bridge of historical significance, I feel, and one I always felt should be modeled (BTW, there was an identical bridge along that line over Oldman's Creek in Pedricktown, but authorities long ago declared that waterway closed to bigger boats and the bridge was replaced with a fixed deck girder type crossing - so the Paulsboro bridge is the last remaining example of this moveable type).
As far as I know, it's still there, still functions (although, there's not much boat traffic these days), and anyone who's in South Jersey and might be interested in replicating this, please do visit Paulsboro and have a look.
[update] Photo attachment failed. look for second attempt downthread.