Natchez Trace Parkway Bridge

The Natchez Trace Parkway Bridge is a concrete double arch bridge located in Williamson County, Tennessee, 8.7 mi from the northern terminus of the Natchez Trace Parkway. It is 1,572 ft long and carries the two-lane Natchez Trace Parkway 145 ft over State Route 96 and a heavily wooded valley. The bridge, also known as the Natchez Trace Parkway Arches, is the first segmentally constructed concrete arch bridge in the United States. The arches comprise 122 hollow box segments precast in nearby Franklin, each of which was about 9.8 ft long and weighed between 26 and 41 metric tons (29 and 45 short tons) . The deck consists of 196 precast post-tensioned trapezoidal box girder segments, each typically 8.5 ft long. The sections atop the crown of the arch are 13 ft deep. The foundations and piers of the bridge were cast in place. The 582 ft long main span is symmetrical, while the 462 ft long second arch is not, due to the slope of the valley at the southern end of the bridge. The bridge is rare in that it does not use spandrel columns to support the deck from the arch. Rather than being evenly distributed along the arch's length, the weight of the bridge is concentrated at the crown of the arch. The lack of spandrel columns results in a clean, unencumbered appearance: it is termed a cathedral arch bridge.