Nps Form 10-900 - National Register Of Historic Places Registration Form Page 12
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22United States Department of the Interior
National Park Service / National Register of Historic Places Registration Form
NPS Form 10-900
OMB No. 1024-0018
Bridge No. 4969
Morrison County, MN
Name of Property
County and State
over the Rainy River (1912), the Dan Patch Line Bridge over the Minnesota River (1910;
highway portion removed), and the St. Paul Terminal Railway Bridge over the Mississippi River
(1895; partially razed), incorporated plate girders in their superstructures, generally but not
universally in the approaches, while the focal spans incorporated trusses of various types. The
fifth, the Interstate Toll Bridge over the St. Louis River (1895-razed), featured wood trestle
approaches leading to Parker through-truss spans that flanked either side of a central truss swing
span. Railroad traffic on this bridge was separated from vehicular traffic by the trusses, while
the Oliver and the St. Paul Terminal Railway bridges used separate decks. Although trucks on
the International Falls-Fort Frances Bridge are required to share the west side of the deck with
rail traffic because of weight restrictions, automobile traffic is separated from it by concrete
barriers and a fence running adjacent to a pipeline that extends down the center of the bridge.
The Dan Patch Line Bridge carried railroad and vehicular traffic on the same deck, and while
minor, a barrier was present in the form of a line of wood beams that were sheathed with metal
on the highway side.
A shared-deck, steel through-truss alternative was prepared for Bridge No. 4969, which would
have been built at a substantially lesser cost, but ultimately, the plate girder option was chosen.
Per an agreement between the Northern Pacific and Morrison County, made official on March 5,
1930, the railroad would be responsible for designing the bridge and supplying plans and
specifications to the county, who would then let the construction contract (Bridge No. 4969
Correspondence File, Minnesota Department of Transportation; Poore 1930b).
The plans provided for a bridge that was 410 feet and 3 inches in length from “parapet to
parapet” (Plans dated March 4, 1930, for “Bridge over Mississippi River for National Guard
Encampment near Topeka, Minn.,” Bridge No. 4969 Correspondence File, Minnesota
Department of Transportation), with a 24-foot-wide roadway and adjacent 5-foot-wide raised
sidewalk with curb. The railroad track was centered in the roadway, with partially embedded
rails spaced at 4 feet, 11-1/4 inches on center supported by embedded steel ties measuring 8 feet
and 11 inches transversely to the rails, and the ends of the ties were supported by the interior two
lines of plate girders. The latter were set lower than their exterior counterparts to accommodate
the railroad track while maintaining a level roadway. They incorporated partial-depth stiffeners
alternating with the full-depth stiffeners at two feet on center on the interior, as well as upper and
lower lateral cross-bracing and vertical cross-bracing between them to provide extra support for
rail traffic loads. The railing was ornamental steel, with six-inch H-beams at regular intervals
between sets of 3/4-inch bars on 4-inch centers (Plans dated March 4, 1930, for “Bridge over
Mississippi River for National Guard Encampment near Topeka, Minn.,” Bridge No. 4969
Correspondence File, Minnesota Department of Transportation).
Although the railing was
atypical for highway use, Michael J. Hoffman (1930), Bridge Engineer for the State Department
of Highways, determined that “the use of a 10 inch curb on the bridge [would] provide the
essential safeguard for highway traffic.” Likewise, although the lack of elements separating
vehicular and railroad traffic was unique, a newspaper article announcing the near-completion of
the bridge gave assurance that “all trains over [the] spur [would] operate under special guard, so
that the public [would] be fully protected” (Little Falls Daily Transcript 1930c). The contract to
Section 8 page 12
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