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This is a very unique bridge. It is a double-deck bridge, with the top level carrying a highway and the lower level carrying a railroad line. Double-deck bridges are rare, nationwide. The main span of the bridge is a vertical lift bridge of unusual appearance. The unusual appearance is because bridges from this period usually had lift towers that were trussed, and often were broader at the base. However, this bridge has towers that on the sides are metal plate giving them a solid appearance. The towers also maintain the same width from top to bottom. The bridge has an extremely long and complex approach system consisting of deck truss and deck plate girder spans. The deck plate girder spans appear to have structurally separate load-bearing superstructures, one for the highway level and one for the railroad level. In contrast, the truss spans have one unified superstructure... each truss web supports both the upper and lower level. The railroad deck of the bridge ends sooner than the highway bridge at each end because the highway, being on the upper deck, must continue to pass over the railroad tracks until they curve away, and also the highway, being on the upper deck, has to have enough additional approach spans to bring the road back to ground level. Finally, perhaps the rarest and most unusual detail of the bridge is that one of the deck plate girder spans for the railroad is an example of one of the rarest general movable bridge categories: a retractile span. The deck plate girder span lifts up and slides back on top of an adjacent truss span. This span is kept retracted unless a train is coming. The retractile span itself is unusual and significant in its own right. It is also unusual for a single bridge structure to have two movable spans. Normally only one movable span is provided, usually in the center of the bridge where the main navigation channel is.
Information and Findings From Maine's Historic Bridge Inventory
Discussion of Bridge
The 1940 vertical lift bridge designed by Harrington & Cortelyou (Harrington was formerly associated with J.A.L. Waddell and is credited as being the mechanical engineer responsible for the development of the vertical lift bridge type) of Kansas City. Its design reflects mid-20th century refinements in the vertical lift bridge type, most notably the arrangement of the operating system with the drive motors and synchronous motors located at the top of the towers. It is the only vertical lift bridge in Maine with this operating arrangement. The bridge also has handsome, Art Moderne detailing. It was named in 1980 for Sarah Mildred Long, the longtime interstate bridge commission's secretary. The 1940 vertical lift bridge is judged to have high preservation priority because of the technological significance of the arrangement of the operating machinery.
Bridge Considered Historic By Survey: Yes
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