The Mogollon Rim Viaduct completed in 1990, is a cast-in-place, post-tensioned box girder bridge with a record breaking, curved 340 foot main span. The bridge is situated on State Route 260 near the top of the Mogollon Rim between Payson and Show Low Arizona. The original alignment was constructed on fill that for years had an overall slope instability. When the slope failed, retaining walls were designed to solve the slope stability problem and to widen the roadway. However, problems developed during construction and this concept was abandoned. The widening and slope flattening resulted in fills extending 700 feet down the slope and was not an environmentally acceptable solution on U. S. Forest Service Land, so a bridge solution was developed.
The Mogollon Rim Viaduct is a unique bridge constructed in a very unique site. This structure required the resources of the latest technology for the analysis and design. ADOT's Bridge Group designers utilized the state-of-the-art computer programs and for some details developed their own computer programs. The bridge also required sophisticated construction methods and quality control measures beyond the ordinary bridge construction practice. Even with the unforeseen construction difficulties, this bridge will prove to be the best choice for the site in terms of overall constructability, economy and long-term durability.
