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The communities along Connecticut's coast and navigable rivers have relied on movable bridges since Colonial times. Wherever highways and waterways intersected, some method of raising the bridge was needed to allow passage of tall-masted vessels. The first movable bridges were short wooden bascules, hinged at one end like medieval drawbridges and raised by a system of ropes and pulleys. Later, large timber-truss swing bridges came into use. Pivoting on a central pier, they offered two channels, one on either side of the pivot pier.
Improvements in metal-truss technology allowed the construction of larger and stronger swing bridges. In addition to the trusses themselves, the many specialized components of swing bridges underwent constant development in the late 19th century. Motive power changed from hand-cranks to steam engines to electric drive; phosphor-bronze center-bearing pivots replaced the iron rollers used on the earliest bridges; and attention to small details such as drive gears and end locks resulted in greatly improved operation.
By 1900, however, bascules had eclipsed swing bridges for all but the longest spans. Steel girders, carefully machined trunnions (the axles that bear the weight of the bascules as they open), concrete counterweights, and steam or electric-driven gearing replaced the timber bascule technology of an earlier era.
Bascules offered many advantages over swing bridges. They could more easily be built in congested settings, they provided a single wide channel rather than two narrower ones, and they could be opened part-way for smaller boats.
Throughout the 1890s and early 1900s, engineers patented many innovations in an attempt to lower the bascule's costs, provide greater reliability, and alleviate the stresses which constant operation placed on trunnions, drive mechanisms, and piers. Eventually, however, increasing motor-vehicle traffic made even brief delays for bridge openings unacceptable. In the late 1930s and 1940s, the State Highway Department began replacing movable bridges with high-level crossings such as Middletown's Arrigoni Bridge.
Take a virtual tour of Connecticut's historic movable bridges via the links in the sidebar to the left.