IAIS Sylvan Slough Bridge

Through Girder Bridge over Sylvan Slough
Rock Island, Rock Island County, Illinois

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Name IAIS Sylvan Slough Bridge
Built By Chicago, Rock Island & Pacific Railroad
Contractor Fort Pitt Bridge Works of Pittsburgh
Currently Owned By Iowa Interstate Railroad
Length 705 Feet Total, 105 Foot Main Spans
Width 2 Tracks, 1 In Use
Height Above Ground 15 Feet (Estimated)
Superstructure Type Through and Deck Plate Girder
Substructure Type Stone Masonry and Concrete
Date Built 1924
Traffic Count 6 Trains/Day (Estimated)
Current Status In Use
IAIS Bridge Number 1816
Significance Local Significance
Documentation Date December 2017
In 1852, the Chicago and Rock Island Railroad began construction of a 40 mile route from Chicago to the nearby city of Joliet.
With the first segment completed, the railroad continued constructing another 119 miles of track to Geneseo. By 1854, the remaining portions of track were constructed into Rock Island, Illinois; located on the Mississippi River.

The first bridge across the Mississippi River would be built connecting Davenport to Rock Island in 1856. After a fire and collapse later that year, the bridge was rebuilt and would begin carrying traffic into Iowa.
Later in 1856, the Mississippi and Missouri Railroad would begin construction on a pair of main lines in Iowa. One route went towards Missouri, while the other continued on the straight west trajectory.
The first 55 miles on the western mainline saw the connection of Davenport and Iowa City by the end of 1856. Another 31 miles to Marengo would be completed by the end of 1862.

These two railroads would become part of the Chicago, Rock Island & Pacific Railroad in 1866. The Rock Island later saw the completion of the route to Nebraska.

As traffic continued to build on the line, it was continuously upgraded. The route through Illinois was double tracked in the 1890s, and the route to Iowa City was double tracked by 1900.
However, this double track proved unnecessary and was removed in the 1930s. Because of the Rock Island Railroads poor management, the railroad oftentimes found itself in financial trouble; despite having a solid core of routes.
Between World War II and 1980, the railroad saw even harder economic downturns. Failed mergers and poor money management led to the inevitable downfall of the railroad.
By 1980, the railroad was officially bankrupt for the final time. Trustees saw the liquidation of the railroad, which sold off and abandoned many lines.

However, as this was the core main line of the Rock Island, it saw a positive future. After an earlier railroad failed in the early 1980s, the Iowa Interstate Railroad was formed in late 1984 to operate over track between Ottawa, Illinois and Omaha, Nebraska.
Since its original forming, the IAIS has turned a once dead mainline into a thriving alternative to Interstate 80. Today, this segment is known as the 1st Subdivision.

View an article regarding the construction of this bridge.

This large girder bridge crosses Sylvan Slough just east of the Government Bridge.
Built in 1924, it replaced a through truss bridge. While it is reported that the old truss bridge ended up at two different locations in nearby Milan, Illinois; the author has serious doubts about these claims.

Historic Photo
Plan of the current and previous bridge, from the Railway Age-Gazette; Volume 75

Currently, the bridge contains five through girder spans and a single deck girder span. The deck girder span was built well before the through girders, but was replaced in approximately 2014. The entire structure sits on concrete substructures.
While it was built for two tracks, only one is currently in use. The unused track has been fenced off.

Historic Photo
Construction of the current bridge, from the Railway Age-Gazette; Volume 75

The author has ranked this bridge as being locally significant, due to the common design and newer age.
The photo above is an overview. The bridge can be easily accessed from a trail on the east side.

Mississippi River Railroad Bridges
Upstream (Sylvan Slough) Sylvan Island Railroad Bridge
Main Channel Government Bridge
Downstream Crescent Bridge


Source Type


Build Date Historic Article
Contractor Historic Article
Railroad Line History Source ICC Valuation Information, Compiled by Richard S. Steele

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