MDT outlines plan to replace three timber bridges on Old U.S. Highway 10 with box culverts

Jacob Brotzler, a Montana Department of Transportation engineer, told Treasure County commissioners the department plans to replace three small timber bridges on Old U.S. Highway 10 with precast box culverts. "We're thinking probably about 30 days total" at each site if the roadway is closed during construction, Brotzler said, though he described that as an early approximation and tied the schedule to funding and permitting.

DOT provided plan sheets showing two side‑by‑side boxes at some locations and single large boxes at others, and said hydraulic engineers sized the culverts to handle infrequent, high‑flow events even when the visible channel is a small trickle. Brotzler said the project is currently about two‑thirds through design and that the letting (preliminary) is listed as March 2026. He estimated the preliminary construction cost around $3 million.

County commissioners raised local concerns: narrow single‑lane bridges on frontage roads, posted weight limits on potential detour routes, and the potential for increased traffic on Yellowstone Frontage Road if locals and curious drivers use it to bypass closures. Brotzler said MDT had coordinated with irrigation companies where crossings are on irrigation channels and that those sites sometimes require additional environmental review because culverts can affect fish passage; he noted, "FWP doesn't like culverts as much because there's a potential for fish perching and it impacts fish passage."

DOT described design choices intended to maintain the existing roadway width (22 feet) and to match existing 3:1 slopes at end sections to avoid adding guardrail and to preserve a traversable roadside slope. Commissioners and DOT agreed further discussion is needed about detour routing and allowable county roads for any official detour; DOT noted the county's formal role would be to approve detour routing on county roads.