Tunkhannock Viaduct

Railroad bridge in Pennsylvania, U. S.

Tunkhannock Creek Viaduct (also known as the Nicholson Bridge and the Tunkhannock Viaduct) is a concrete deck arch bridge on the Nicholson Cutoff rail line segment of the Norfolk Southern Railway Sunbury Line that spans Tunkhannock Creek in Nicholson, Pennsylvania. Measuring 2375 feet (724 m) long and towering 240 feet (73 m) when measured from the creek bed (300 feet (91 m) from bedrock), it was the largest concrete structure in the world when completed in 1915 and still merited "the title of largest concrete bridge in America, if not the world" 50 years later. Built by the Delaware, Lackawanna and Western Railroad (DL&W), the bridge is owned today by Norfolk Southern Railway and is used daily for regular through freight service. The DL&W built the viaduct as part of its 39.6 mile (64 km) Nicholson Cutoff, which replaced a winding and hilly section of the route between Scranton, Pennsylvania, and Binghamton, New York, saving 3.6 mile (6 km), 21 minutes of passenger train time, and one hour of freight train time. The bridge was designed by the DL&W's Abraham Burton Cohen; other key DL&W staff were G. J. Ray, chief engineer; F. L. Wheaton, engineer of construction; and C. W. Simpson, resident engineer in charge of the construction. The contractor was Flickwir & Bush, including general manager F. M. Talbot and superintendent W. C. Ritner. In 1990, the National Railway Historical Society placed a historical plaque on the structure noting its size as the world's largest concrete bridge, completing the Summit cut off project for the Delaware, Lackawanna and Western Railroad.

Construction on the bridge began in May 1912 by excavating all 11 bridge piers to bedrock, which was up to 138 feet (42 m) below ground. In total, excavation for the viaduct removed of material, more than half of that rock. Almost half of the bulk of the bridge is underground. At mid construction, of concrete had gone into its substructures, and it was estimated that construction would require of concrete and of steel. The steel estimate proved accurate; the bridge ultimately used a bit less concrete than expected: , making the total weight approximately
The bridge was dedicated on November 6, 1915, along with the opening of the Nicholson Cutoff. Construction photos along with a short history of the bridge were published by the Nicholson Area Library in a brochure in 1976. It was listed on the National Register of Historic Places on April 11, 1977. the local community has celebrated the building of the bridge on the second Sunday of September with "Nicholson Bridge Day", a street fair, parade, and other activities. The 100th anniversary celebration was held in September 2015.

In 1975 the American Society of Civil Engineers or ASCE designated the bridge as a National Historic Civil Engineering Landmark. ASCE noted that at the time of its construction from 1912 to 1915, it was the largest reinforced concrete railroad bridge ever built. ASCE recognized the bridge as "not only a great feat of construction skill" but also a "bold and successful departure from contemporary, conventional concepts of railroad location in that it carried a mainline transversely to the regional drainage pattern, effectively reducing the distance and grade impediments ". At the time, the decision was made to build the bridge out of reinforced concrete, railroad engineers had little experience with this material. The bridge was also listed on the National Register of Historic Places on May 3, 1977. In 1990, the National Railway Historical Society placed a historical plaque on the structure noting its size as the world's largest concrete bridge, completing the Summit cut off project for the Delaware, Lackawanna and Western Railroad.