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Hales Road Bridge,
Bridge No. 3852
• Hales Road over Metro North
• Steel Warren pony truss
• Length: 53'
• Built in 1891
Hales Road Bridge is one of four remaining trusses built as part of the New Haven Railroad's upgrading of its New York to New Haven corridor in the early 1890s. That project, which widened the right-of-way from two to four tracks, straightened curves, and eliminated grade-level crossings, required scores of new bridges to carry local highways over the rail line. Most were steel rivet-connected pony trusses like this bridge.
These bridges represent the oldest riveted trusses in Connecticut and one of the first large-scale programs of riveted highway-bridge construction. Compared with the pinned technique that dominated American bridgebuilding at the time, riveted joints offered greater rigidity and simplified connections. Because railroad bridges needed rigidity, they were the first to make extensive use of riveted trusses, and railroad-built highway bridges soon followed. With improvements in field-riveting, riveted trusses could be assembled as easily as pinned bridges.
Although the bridge's Warren-truss pattern, use of steel rather than wrought-iron, and riveted connections prefigured the small highway bridges of the 20th century, its details depart from what eventually became standard engineering practice. Among its unusual features are the bent-bar interior lattice on the underside of the top chord, the direct riveting of components rather than using gusset plates, and flat bars instead of angles for the uprights. Each of these items saved the railroad money, an important consideration given the scale of the project, and was adequate to meet the load-bearing requirements of the bridge. Such details, however, reflect an experimental stage in riveted truss design.