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Located deep within the heart of Michigan’s beautiful Upper Peninsula is Marquette County’s Humboldt Township. It is a community with a rich history of commerce in the industries of mining and logging, steeped in generations of family traditions, and wrapped in the natural splendor of the Upper Peninsula. One might as easily see a construction crane or a sand hill crane, a regal moose, or a wood harvester, a magnificent Northwoods cabin or rustic sauna, all by traveling its’ weathered roads and bridges, including Marquette County’s 478. Regrettably, weathered, because it is one more rural area with worn out infrastructure needs lacking sufficient funds to bring the community’s assets to an acceptable standard, including bridges.

Co.Rd. 478 is considered one of Marquette County’s primary roads. It provides the vital access to first responders and motorists as it winds through the heart of Humboldt Township and over the Black River. However, decades of service and deterioration resulted in the Black River bridge being considered structurally deficient. The challenge to the residents, the County, and its’ consultant, AECOM, was to find a suitable bridge that would meet current regulatory standards both hydraulically and structurally, while being constructed in a minimum of time and at an affordable cost. Ideally, it should be a structure that could provide the rare economic benefits of being both Least Initial Cost and Least Life Cycle Cost while meeting the Every Day Counts rapid construction criteria all within the Michigan Department of Transportations’ bridge requirements*. Due to the longer span width and shallow profile, conventional thinking would point to a traditional beam and deck bridge effectively negating any prospects of accomplishing these desired economic benefits.

Unconventional and innovative thinking by the Township, County, and Engineer was the order of the day. They determined there really was only one viable solution that met all those desired benefits, LowSpan. LowSpan is a prestressed 3-sided culvert that could meet the rigid MDOT HL 93 MOD* standards with its’ 47’ span width yet provide the necessary site-specific 7’ low-rise profile. Precast wingwalls and headwalls completed the bridge from the foundation up (less guardrails). Truly a complete bridge delivered on a truck(s).

Perhaps its’ best to let the stakeholders describe the attributes and benefits of the new Marquette Co.Rd. 478 bridge, Humboldt Township unveils new Black River Bridge (uppermichiganssource.com).