Zoo Interchange Rail Bridge

Quadrangular Through Truss over Hank Aaron State Trail
West Allis, Milwaukee County, Wisconsin

Click the Photo Above to See All Photos of This Bridge!
Name Zoo Interchange Rail Bridge
Built By Milwaukee, Sparta & Northwestern Railway
Contractor (Superstructure) Pennsylvania Steel Company of Steelton, Pennsylvania
Contractor (Substructure) Cleary-White Construction Company of Chicago
Currently Owned By Union Pacific Railroad
Length 170 Feet Total
Width 2 Tracks
Height Above Ground 25 Feet (Estimated)
Superstructure Type Quadrangular Through Truss
Substructure Type Concrete
Date Built 1910
Date Closed 2015
Traffic Count 00 Trains/Day (Bridge is Bypassed)
Current Status Bypassed and Closed
Former UP Bridge Number 89.81
Significance Moderate Significance
In 1910, the Milwaukee, Sparta & Northwestern Railroad would begin construction on a beltline around the west side of Milwaukee, to bypass the traffic in the core of Milwaukee.
At the time, the route to the Twin Cities was complicated for the Chicago & Northwestern, and involved going through Madison, Baraboo and La Crosse to Mankato.
During the same time, the Milwaukee, Sparta & Northwestern was working on a line which connected the northwest corner of Milwaukee to Wyeville, and ultimately Eau Claire, which provided a direct link.
The newly constructed beltway around West Allis provided a link to the new mainline from the current C&NW line around South Milwaukee.
When completed, the C&NW quickly took a controlling stake in the MS&NW, and absorbed the company.
The line was only 8 miles long, but one of the most significant in Wisconsin. The new construction included the massive Butler Yard on the far northwest side of Milwaukee.
North of the Butler Yard, the line would have an intersection with two other lines, built at the same time. One heading west, one heading east.
Dropping south through the Butler Yard, the line closely paralleled the Menomonee River and what is currently I-41 (Zoo Freeway).
Continuing, the line would cross the Milwaukee Road mainline between Saint Paul and Milwaukee, as well as Underwood Creek and a toll road towards Watertown, all on the same bridge.
Next, the line crossed what is now I-94, and crossed a secondary Milwaukee Road Line, which was the previous mainline.
The line eventually ended at a wye, where it met the line around the south side of Milwaukee, and the line towards Waukesha and Madison.

The line is known for being heavily engineered, including some of the technical marvels at the time, such as its trusses.

Today, with the acquisition of Chicago & Northwestern in 1995, the Union Pacific owns and operates the line as a fairly used mainline. While the bridge across the southern Milwaukee Road line was replaced in 2014, the line still retains much of its original integrity and components.

View an article regarding the construction of this route.

Located in West Allis, this iconic bridge is located near the Milwaukee Zoo, and the "Zoo Interchange."
Built in 1910, the bridge was used to cross the main line of the Chicago, Milwaukee & St. Paul Railway (Milwaukee Road).
Heavily built, the bridge features a single Quadrangular Through Truss span, with M-frame portals and riveted connections. It rests on concrete substructures.
This design of truss was commonly used on select railroads starting in the late 1870s. The design was popular due to the redundancy built into the members, which would generally prevent the bridge from collapsing if a train derailed.
First pioneered by Charles Hilton at the Leighton Bridge & Iron Works, the spans then were often built by the Lassig Bridge & Iron Works through the 1880s and 1890s. When that company was merged into American Bridge Company in 1900, American Bridge would commonly build these spans.
This span represents a shift in contractors, as Pennsylvania Steel won the contract to construct the truss structures on this line. Prior to the Milwaukee, Sparta & Northwestern constructing the variety of quadrangular through trusses across Wisconsin in 1910-1911, the design had fallen out of favor with several railroads.
Today, the bridge stands bypassed by a new bridge, built as part of the reconstruction of the Zoo Interchange. It crosses the Hank Aaron State Trail. The future of the truss is largely unknown, but the preservation is a unique example of a DOT recognizing the significance of a railroad bridge.
Overall, the bridge appears to be in fair condition, with minor defects noted. The author hopes to return to this bridge in the future for better photos.

The author has ranked this bridge as being moderately significant, due to the truss design.
The photo above is an overview.


Source Type


Build Date Pennsylvania Steel Company plaque
Contractor Pennsylvania Steel Company plaque
Railroad Line History Source ICC Valuation Information, Compiled by Richard S. Steele

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