Mystic River Highway Bridge

The Mystic River Bascule Bridge carries U.S. Route 1 and Main Street over the Mystic River at Mystic, Connecticut. Completed in 1922, the single-leaf deck plate girder bascule was the concluding element of the State Highway Department’s improvement program for coastal Route 1, then the principal trunk line highway of the state. ¹ It is among the few surviving examples of the Brown Balance Beam bascule, a form that raised movable bridge technology to a new level of refinement in the early twentieth century.

Design and Construction

The counterweighted four-bar linkage bascule was the work of Thomas Ellis Brown, a former Chief Engineer of the Otis Elevator Company who practiced in New York as a consulting engineer. Brown patented the balance beam configuration in 1918. ^{1 3} The Mystic design was prepared by his firm, Thomas E. Brown & Son, together with Waddell & Son. The American Bridge Company fabricated the steelwork, and the J. E. Fitzgerald Construction Company of New London, Connecticut, erected the structure. The bridge opened to the public on July 19, 1922, replacing a crossing of 1904. ² Until 1928 it also carried the streetcars of the Groton & Stonington Street Railway.

The bascule leaf is raised with the assistance of two reinforced concrete counterweights of 230 tons each, carried at the ends of overhead trusses, or balance beams, that pivot on a tower structure at the west end of the span. ¹ Linkage arms run from the east ends of the balance beams to the tops of the bascule girders, so that the descending counterweights drive the leaf upward through the linkage. Power is supplied by two 40 horsepower direct current motors, each weighing 1,400 pounds, which turn bull wheels connected by a further set of linkages to the two plate girders of the movable span.

The original deck of thick wooden blocks was replaced with open steel grating in 1935, and a steel plate covering was added over the two concrete counterweights in 1937. ¹ The operator’s house, originally a single-level structure, was rebuilt as a two-level building at some point between 1936 and 1955. The Cutler-Hammer operating console dates from the 1950s, with the exception of an original Westinghouse hydraulic brake controller that was retained in service.

Rehabilitation

The bridge was rehabilitated in two phases between 2000 and 2013. ³ The work included deck replacement, structural repairs, replacement of the operating machinery, upgrades to the electrical systems, and repainting of the superstructure. The later phase addressed settlement of the substructure, which had thrown the upper balance truss and the span drive machinery out of alignment. The principal supporting components of the balance truss and balance link were replaced, and new span drive machinery was installed to current standards. The Connecticut Department of Transportation carried out the project with TranSystems Corporation of Connecticut as lead designer and Cianbro as general contractor, scheduling the work across three short winter seasons in order to avoid the tourist and boating months. Lead paint and asbestos required extensive containment, and a jacking and shoring system of paired W36 beams supported the counterweights so that pile driving in the navigation channel could be avoided. ⁴

Operation

The bridge is operated by the Connecticut Department of Transportation and carries an average daily traffic of 11,800 vehicles. ¹ It opens approximately 2,200 times a year, each opening lasting about five minutes, chiefly to pass sailboats and yachts. From May 1 to October 31 it opens hourly during daylight at forty minutes past the hour, and on demand at other times. The span is greased and inspected every one hundred openings, or every two weeks during the winter.