M-86 Truss Bridge Rehabilitation and Relocation

Complex Bridge Restoration and Relocation Preserves Local History and Enhances Area’s Natural Environment

The Michigan Department of Transportation (MDOT) partnered with OHM Advisors to salvage and rehabilitate the historic “M-86 Bridge”, originally constructed in Detroit in 1923 and the last of its kind on any state trunkline route. Moved to its then-location over the Prairie River in St. Joseph County in 1938, the single, 84-foot-span riveted steel camelback pony truss bridge had suffered significant deterioration and did not have adequate width shoulders to carry the roadway’s two lanes of MDOT trunkline traffic. MDOT desired to replace it with a wider structure and restore and relocate the historically designated bridge to a lower volume road over the Dowagiac River in Cass County, nearly 50 miles away.

Working closely in cooperation and coordination with MDOT, the State Historic Preservation Office (SHPO), and the Cass County Road Commission, our team created the designs for the new bridge foundations, restoration of the existing steel truss bridge with painting and steel repair/replacement, replacement of the bridge deck and railings, and construction of the approaches at the new location—which included preservation of state-protected wetlands and endangered plant species. The bridge to be replaced in Cass County had a slight skew and a 50-foot span, and although the M-86 bridge span was sufficient for replacement, it was not skewed and challenged our design team to accommodate the skewed alignment of the river as well as a curved roadway alignment.

Our team also prepared demolition plans for the existing M-86 site foundations and designed detailed bridge relocation plans—which included developing pay items, detailed cost estimates and logistics for the disassembly, rehabilitation, transport and reassembly of the bridge on the new site, as well as review of the proposed 50-mile transportation route to ascertain any needed roadway improvements to accommodate the move. Ultimately, the project contractor decided to dismantle and transport the bridge in shorter sections to an enclosed facility in Ecorse, MI for steel sand blasting and restoration. Our team assisted MDOT during the construction phase with visits during the dismantling at M-86, the restoration in Ecorse, and reassembly in Cass County. 

Integral to the project’s success was the collaboration between multiple stakeholders and project team members in combination with important public feedback from the community—all of which resulted in the preservation and delivery of a uniquely historic, award-winning bridge to Cass County that enhances the natural environment in this area of the Dowagiac River.

Project Highlights: bridge inspection, bridge design, historic bridge restoration, historic bridge repair and replacement, historic bridge relocation, roadway approach design, floodplain hydraulic analysis, construction management