CN Mill Creek Bridge (Dunlap)

Dunlap, Harrison County, Iowa

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Name	CN Mill Creek Bridge (Dunlap) Illinois Central Railroad Bridge #WA468.5
Built By	Illinois Central Railroad
Currently Owned By	Canadian National Railway
Superstructure Contractor	Unknown
Substructure Contractor	Unknown
Length	88 Feet Total, 60 Foot Main Span
Width	1 Track
Height Above Ground	15 Feet (Estimated)
Superstructure Design	Through Plate Girder and Concrete Slab
Substructure Design	Concrete Pile
Date Built	1915, Using a Span Fabricated 1901
Original Location	Bridge #J390.98; Bayou Gayoso Bridge; Memphis, Tennessee
Traffic Count	2 Trains/Day (Estimated)
Current Status	In Use
Illinois Central Railroad Bridge Number	WA468.5
Canadian National Railway Bridge Number	468.5
Significance	Local Significance
Documentation Date	12/30/2018

Between 1857 and 1870, the Dubuque and Sioux City Railroad (D&SC) had acquired and constructed a mainline across central Iowa, extending from the Mississippi River at Dubuque, Iowa to the Missouri River at Sioux City, Iowa. The D&SC had operated under lease from the Illinois Central Railroad (IC) since 1867, and connected to the IC system by using a bridge across the Mississippi River at Dubuque. This line provided several opportunities for the construction of branch lines. By the late 19th Century, the IC desired to enter the Council Bluffs, Iowa/Omaha, Nebraska markets. In 1890, the Omaha Bridge & Terminal Railway (OB&T) began construction on a line extending between Council Bluffs, Iowa and Omaha, Nebraska. A new bridge was constructed across the Missouri River between 1893 and 1894, with the goal of breaking the Union Pacific Railroad (UP) monopoly of traffic crossing the Missouri River at Omaha. Between September 1898 and January 1900, the Fort Dodge and Omaha Railroad (FD&O) constructed a 131-mile railroad line, extending from the existing D&SC mainline at Tara, Iowa to Council Bluffs, Iowa. The FD&O and OB&T were both leased by the D&SC/IC in 1899.

By the late 19th Century, the IC had developed and operated a sprawling railroad network in the central United States. This line served as a secondary mainline for the company, connecting Chicago to the Missouri River at Omaha. In the 20th Century, the IC had become a respected railroad, connecting several major cities in the central United States. The D&SC was fully merged into the IC in 1946. In 1972, the IC merged with the Gulf, Mobile & Ohio Railroad (GM&O) to form the Illinois Central Gulf (ICG). The bridge across the Missouri River was placed out of service in approximately 1980, although the tracks remain today. The entire IC system in Iowa, as well as the line between Dubuque and Chicago, were sold to the Chicago Central & Pacific Railroad (CC&P) in 1995. In 1988, the ICG was reorganized as the Illinois Central Railroad (IC). In 1996, the CC&P was repurchased by IC and in 1998, IC was purchased by the Canadian National Railway (CN). Today, CN operates the Omaha Subdivision between Tara and Council Bluffs.

Located alongside US Highway 30 between Dunlap and Woodbine, this through plate girder and trestle bridge carries a former Illinois Central Railroad mainline over Mill Creek adjacent to the former Chicago & North Western Railway bridge. The first bridge at this location likely consisted of a timber pile trestle bridge, constructed when the line was first built. In the mid-1910s, the IC made several upgrades to this line, primarily replacing timber bridges with secondhand steel spans. In 1915, the bridge was rebuilt and a through plate girder span was installed. Currently, the bridge consists of a 60-foot through plate girder span, approached by a 14-foot concrete slab span on either end. The entire bridge is set onto concrete pile substructures, which are capped with concrete bridge seats. Somewhat unusual, a nearby bridge was constructed 1916 with a nearly identical center span, but instead uses timber approaches and substructures. The main span follows a standard design, consisting of two heavy plate girders, rounded girder ends and an open deck. This span was fabricated in 1901 for use at Bridge #J390.98, which crossed Bayou Gayoso in Memphis, Tennessee. Several steel spans placed on this line during this era were used from both nearby locations as well as from other far away places on the IC system. The approaches also use a standard IC design, consisting of standard concrete slab spans, which are set onto concrete pile substructures. An unknown firm fabricated the girder span, and it is unclear if the concrete portions were constructed by an unknown contractor or railroad company forces. Through plate girder spans were popular for railroad use, as they were durable and easy to construct. Railroads often reused steel and iron spans, as it provided a cost effective way to upgrade bridges without requiring large amounts of new material. Since the initial construction, the bridge has seen periodic renewal of the timber approaches, and remains in regular use. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being locally significant, due to the common design.

Citations

Build dates and relocation history	Illinois Central Railroad Valuation Engineering Field Notes at the National Archives
Railroad History Citation	ICC Valuation Information, Compiled by Richard S. Steele