Project Overview

Montana Highway 86 (MT 86) is a scenic route winding through rural farmland and recreational areas, frequented by travelers journeying from Wilsall to Bozeman via Bridger Canyon. Along the way, they cross small creeks on timber bridges, many constructed in 1939 that have undergone regular maintenance over the years. However, no structure can be expected to last indefinitely, especially under the strain of increasingly heavier loads and growing traffic volumes.

The Montana Department of Transportation (MDT), in collaboration with the engineering firm Morrison-Maierle, is working to replace three of these timber bridges through the MT 86 Structures project. The three timber structures being replaced include the bridges over Cache Creek, Carrol Creek, and Flathead Creek. These bridges will be replaced with box culverts, tunnel-like concrete structures.

Bridge Replacement Timing

The project team is currently in the design phase, working on project plans and designing each culvert that will replace the existing timber structure. The project plans are expected to be completed by spring 2026, with construction tentatively scheduled for fall 2026 through summer 2027. The project timeline is dependent on the completion of the design phase and the availability of funding.

Temporary Bridges Installed on MT 86 at Flathead Creek and Cache Creek

Flathead Creek Bridge and Cache Creek Bridge were recently evaluated during the current annual bridge inspections. These inspections assess a bridge’s condition and were used to determine the maximum weight each bridge can safely carry for various vehicle types. This ongoing process is essential for public safety.

Due to their poor condition, Flathead Creek and Cache Creek bridges have been assigned low load postings, which means that even vehicles such as commercial vehicles, agricultural vehicles, and snowplows can no longer cross them. It was also determined that these low load postings would significantly impact this area.

Temporary repairs and mitigation options were considered, but the unique issues of these bridges make traditional repairs unfeasible.

As a result, it was decided that temporary bridges would be installed as a short-term solution to alleviate weight restrictions and restore capacity for highway-legal loads. These temporary structures will remain in place until the original bridges are replaced.

The temporary structures installed at Flathead Creek and Cache Creek are single-lane bridges with a 12-foot width restriction. Vehicles exceeding this width need to take an alternate route.

When approaching the temporary bridges, drivers should expect a reduced speed limit of 35 mph and must yield to oncoming traffic.

The community is encouraged to stay informed about the project's progress and to reach out with questions, concerns, or feedback by emailing Sloane at sloane@bigskypublicrelations.com or calling the project hotline at 406-207-4484, Monday through Friday from 9 a.m. to 5 p.m.

UPN 9805000