Olso Bridge (Bridge 9100)
History and significance
Bridge 9100 carries Minnesota Trunk Highway 1 and North Dakota Highway 54 across the Red River, connecting Oslo, Marshall County, Minnesota, with rural Walsh County, North Dakota. The continuous highway changes route numbers at the state line at the midpoint of the crossing. The 792-foot-long structure is comprised of two steel through-truss main spans, each 220 feet long, and seven steel-beam approach spans, four on the east and three on the west. The main spans are designed as Warren-with-verticals trusses in a camelback type of top chord.
Because of the unusual shifting soils along the Red River, Bridge 9100 has specially engineered approach spans and substructure that flex and allow for movement in the underlying soils while maintaining a stable deck and driving surface. The piers, which do not flex, isolate the main spans from any movement of underlying soil and embankments.
Bridge 9100 is significant for its truss design and is considered eligible for the National Register of Historic Places in North Dakota but considered not eligible in Minnesota because of different contexts for historic bridges in the two states.
City of Oslo (Marshall County)
Latitude, Longitude: 48.194349, -97.140802