Zoo Interchange Rail Bridge

• 1880: 80 miles started between Milwaukee and Madison, Wisconsin by the Milwaukee and Madison Railway
• 1881: M&M acquired by the Chicago, Milwaukee & North Western Railway
• 1882: 80 miles completed from Milwaukee to Madison by the Chicago, Milwaukee and North Western Railway
• 1883: CM&NW acquired by the Chicago & North Western Railway
• 1902: Second track constructed from Milwaukee to West Allis, Wisconsin
• 1908: 2 miles of double track completed from Chase to St. Francis, Wisconsin by the Chicago & North Western Railway
• 1911: 9 miles of double track completed from West Allis to Butler completed by Milwaukee, Sparta & North Western Railway
• 1911: 6 miles of double track completed from Butler to Lindwerm completed by Milwaukee, Sparta & North Western Railway
• 1912: MS&NW acquired by the Chicago & North Western Railway
• 1995: Chicago & North Western purchased by Union Pacific Railroad
• 1995-Present: Union Pacific operates the Milwaukee Subdivision from St. Francis to Butler
• 1995-Present: Union Pacific operates the Shoreline Subdivision from Butler to Wiscona

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.