Thompson Road Bridge

Most Recent Visit To Bridge: April 1, 2006

Key Facts

Bridge Name	Facility Carried / Feature Intersected	Location	Structure Type	Construction Date / Builder or Contractor
Thompson Road Bridge	Thompson Road Over Railroad (Abandoned Yard)	Rural: Cass County, Michigan	Concrete T-Beam, Stationary	1919 By: Unknown

Technical Facts

Structure Length	Roadway Width	Main Spans	Approach Spans
169 Feet (51.5 Meters)	20 Feet (6.2 Meters)	5	None

Sometimes Thompson Road shows up on maps as Thomson Road.

Some people unfamiliar with their history may wonder what this bridge is going over, and why an open field is present all of a sudden here also. MDOT provides a good historic overview of this area, but in short, there used to be a rail-yard here known as "the hump", which is long gone. The bridge remains today as a memory of this past. The bridge itself is both old and significant. The bridge was built in 1919, and is a very early example of t-beam construction. MDOT mentions that it is also unusual because it did not follow the state standard t-beam plan that was available at the time.

This bridge is also noteworthy for an attractive brick deck. Brick decks are surprisingly rare, and very few examples remain today. This bridge retains pole guardrails also. The structure is slightly skewed, which adds to the technological value of the bridge. As a five-span bridge, it is also of significant length.

This is one of the few remaining historic bridges of any kind in Cass County. Despite the fact that it no longer crosses anything, this bridge is worthy of preservation, both as an unusual structure, and a memorial to busier railroading times in this area. The bridge is currently in decent condition, with a 66% sufficiency rating in 2004 in the National Bridge Inventory, which is very high for a bridge of this age, even on a rural road.

Historic Significance Rating (HSR)

Information and Findings From MDOT

The Thompson Road Bridge is eligible for the National Register as an excellent example of an early concrete T-beam bridge with very good historical integrity. This grade separation is among the oldest examples of a concrete T-beam highway bridge in the state.

The design is quite different from the standard T-beam plan which the Michigan State Highway Department had developed in the 1913-1914 biennium, but used sparingly during that decade. The plans for the Thompson Road Bridge were probably developed by the railroad company, which had a switching yard and many associated tracks in the area. The tracks under the bridge were originally operated by the Michigan Central Railroad; later, other companies assumed control over the trackage. The main line of the Michigan Central, which was built in Cass County in 1848, is about one-half mile west of the bridge site.

After the Civil War, a new railroad called the "Air Line" linked Jackson with the Michigan Central line at Niles. Within two years, the Michigan Central controlled the Air Line routes. A 1935 county history notes that a cut-off was built to connect the Air Line route and the main line of the Michigan Central in Howard Township "some fifteen years ago." That date seems to correspond to the 1919 date of the bridge. The wide right-of-way near the bridge was used as a railroad switchyard known as the "Hump."

Visit MDOT's Historic Bridge Website

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