M-64 / Ontonagon River

MDOT Historic Bridge Ontonagon County M-64 / Ontonagon River

County: Ontonagon

City/Township: Ontonagon

Location: M-64 / Ontonagon River

Year Built: 1939     Year Replaced: 2006

About this Bridge:
This steel swing-span bridge carried M-64 in the village of Ontonagon, on the south shore of Lake Superior. The structure was comprised of three deck girder spans: the center movable span, featuring center-pivot, plate girders with variable depths, flanked by two uniform-depth fixed girders. These girders were all made up of steel plate webs, with riveted angle flanges and web stiffeners. The fixed spans rested on concrete abutments and piers with steel sheet piling cutwaters. The pivot pier was a concrete cylinder, also with sheet piling surrounds.

Both fixed and swing spans were floored with asphalt-covered concrete, and both sides of the deck were lined with narrow sidewalks with MSHD standard, Moderne steel guardrails anchored by steel bulkheads. The bridge tender worked from a single-story structure over the upstream side of the pivot span's west end. The Ontongon Bridge extended 309 feet (wit a 110-foot pivot span) and has a 26-foot roadway. When swung, the bridge provided a 30-foot channel for passing water craft.

First settled in 1843 and platted in 1854, the village of Ontonagon is one of the oldest Anglo colonies on Lake Superior. Ontonagon County, also formed in 1843 by the state legislature, encompassed a large part of the Upper Peninsula; it was subsequently partitioned into other counties and further subdivided into townships.

The seat of Ontonagon County and Ontonagon Township, Ontonagon was incorporated as a village in 1885. The town straddled the Ontonagon River at its mouth, and the river became, in historian Knox Jamison's words, "the storehouse and distribution center for the early miners, lumber industry, fishing industry, and even today coal is transported by water to the local paper mill."

The Ontonagon River formed a major avenue for water traffic through the village, but it also formed an impediment to overland traffic on its two sides. One of the village's first official acts was authorization of a bridge across the river in 1891. Located next to the Diamond Match Company's sawmill at the river's mouth, the structure featured pin-connected through trusses and a swing span to maintain a clear waterway for the large amount of riverbourne traffic to Lake Superior.

The Ontonagon Bridge was heavily damaged when the match company's plant burned in 1896. After its reconstruction, the bridge carried increasingly heavy traffic into the new century. The highway through town became a trunk line route in the 1910s and M-64 in the 1920s. By the late 1930s the Ontonagon Bridge had become a serious bottleneck for in-town and regional traffic.

"The old structure was of the truss type which was unsightly as well as entirely inadequate for present traffic on M-64 through Ontonagon," the Ontonagon Herald reported. "It provided only an 18-foot roadway and it was necessary to impose drastic weight restrictions on vehicles using the structure."

In 1938 the Michigan State Highway Department (MSHD) rebuilt the north and south piers of the existing bridge and in 1939 the pivot pier. Later that year MSHD designed a replacement superstructure for the bridge, substituting steel girders for the existing trusses and raising the roadway height by 3 ½ feet. In July 1939 MSHD awarded a contract to build the superstructure to John K. Jackson of Ironwood. Jackson demolished the existing trusses, built a temporary bridge and in January 1940 completed the permanent bridge at a cost of $86,431.00.
The new Ontonagon Bridge was one of the largest bridge projects undertaken to date on the western half of the Upper Peninsula, according to highway department officials. It was one of two movable-span structures undertaken by MSHD in the 1930-1940 biennium.

In 2006, the 60-year-old bridge was replaced due to operational problems. A replacement opened to traffic on October 11, 2006. The new bridge features 13 spans and is nearly 1,700 feet long, including two lanes of traffic and a 12-foot-wide pedestrian lane that will accommodate a trail groomer and snowmobiles in the winter.

Swing-span bridges were built with regularity in Michigan in the 19th and early 20th centuries. With an abundance of navigable rivers and river-level roads and railroads, Michigan provided a natural setting for movable bridge technology. The counties, municipalities and even townships built movable-span bridges to separate overland traffic from river traffic, beginning in the mid-19th century. Most of the earliest movable bridges used swing spans, typically with pin-connected trusses that pivoted over center piers. MSHD generally eschewed swing-span bridges in favor of bascule spans, building relatively few of these center-pivot structures. The Ontonagon Bridge was the last swing-span structure erected by MSHD.