The Toston Structures consist of a 661-foot-long highway bridge—and an adjacent 350-foot-long railroad bridge—over the Missouri River in Montana between Townsend and Three Forks. The structures have intermediate river piers, steel beams and cross frames, and nearly 7,000 square feet of concrete decks between them. Our services included:
- Highway design
- Bridge engineering
- Natural resources
Two Corridors, Two Possibilities
The 75-year-old structures were at the end of their design lives. They also had a treacherous curve with no shoulders, and inspections showed cracking in some critical areas. In 2011, the Montana Department of Transportation (MDT) completed a simulation on the US-287 corridor crossings of the Missouri River and the Montana Rail Link tracks near Toston to look for ways to improve the corridor. This segment was the site of many bad crashes, so in 2013 they selected Morrison-Maierle to take on the project.
Considering soils, irrigation, farmland, businesses, homes, road design, railroad, etc., MDT and Morrison-Maierle looked at ten possible solutions and selected two for additional study—the Central Corridor and the Eastern Corridor, which included a dramatic change for the residents of Toston.
Morrison-Maierle laid out a single alignment within each corridor and completed an alternatives analysis that looked at 12 different design criteria, such as road geometry, hydraulics, and irrigation. We also considered 11 environmental impacts, such as those to wetlands, farmlands, local residents, and the area’s proximity to Quake Lake—an area that showed significant seismic acceleration.
The team produced a report and presented it to the community. In roughly one month, the citizens of Toston petitioned against the Eastern Corridor solution. MDT studied this solution further, took the public’s input to heart, and decided that the Central Corridor design was the best option.
Due to the nature of the underlying soils in this area, we conducted an extensive test pile program that load-tested various pile types, tips, and shoes. As a result of this study, MDT saved approximately $900,000. Bidders used this information in their project estimations to present solutions that would help minimize risks.
We were concerned that two major bridges would take a couple of years to build. To keep the project on schedule, we kept traffic flowing on the existing highway during construction so the contractors could place the new embankment before they built the structures. This strategy kept traffic flowing and created a much broader roadway.
MDT’s records indicated a high number of carcasses along US-287 in this area. Morrison-Maierle designed a wildlife fencing system with animal jump-out structures and experimental electrified mats to keep large animals from crossing the highway. This solution forced deer, elk, and other species to travel under the bridges instead.
Connectivity and Construction
Federal law protects recreational areas—like the nearby fishing access site—from being used for staging or storage during construction. On this project, the contractor negotiated with Montana Fish, Wildlife & Parks to use this access area in exchange for significant improvements. They offset the highway intersection between Toston and Radersburg to provide left-turn bays on both legs without widening the bridge over the river. The design team also provided a pedestrian underpass, connected trails, created a school bus stop, and space for snowplows to turn around.
With the completion of the $30 million Toston Structures, drivers now have the luxury and safety of driving on more than 22 miles on a four-lane highway. The finished product will serve the traveling public for many decades to come.