History

Dolores River Bridge
CDOT Structure K-01-C

History Colorado/National Register Multiple Property Submission



History Colorado/National Register Multiple Property Submission

Built in 1952, the Dolores River Bridge carried Colorado Highway (CO) 90 across the Dolores River east of the community of Bedrock in Montrose County. Located in a remote section of Southwest Colorado, CO 90 was one of the state's earliest highways—initially known as the Paradox Road and, later, State Primary Road No. 20.

This road extended west from Gunnison to Montrose, through Bedrock, where it crossed the Dolores River, and into Utah. In the 1920s, the section of this road from Montrose to the Utah state line was re-designated as CO 90.

The bridge was a late example of a steel, rigid-connected Pennsylvania through truss—a bridge type that derived its name from the Pennsylvania Railroad, which patented the design in 1875 for use by locomotives. The type was later adapted for vehicular traffic, but was not used commonly on Colorado's highways, where the single-panel Parker through truss was a more popular choice.

The steel truss members were fabricated by the Midwest Steel & Iron Works, a company founded in Denver in 1893 that continued to fabricate steel into the 1980s. The Colorado Department of Highways contracted Gardner Construction Company of Glenwood Springs, Colo., to build the bridge at a total cost of $73,688.54.  

The Dolores River Bridge was 125 feet long and supported by concrete abutments and wingwalls, and it featured steel lattice guardrails. Its combined polygonal top chord and subdivided panels distinguishes it from other truss designs, including the Pratt, Whipple, Baltimore, and Parker. Its simple design made it easier to construct than these truss types.

In 2002, it was listed on the National Register of Historic Places as an important transportation-related resource and as intact example of a Colorado Highway Department truss design. It was the only Pennsylvania through truss bridge identified in CDOT's 2000-2002 statewide historic bridge inventory. 

In September 2014, a crack was discovered in a vertical truss member, resulting in closure of the bridge. This crack was the result of stresses induced in the vertical truss member from vehicle impacts to the sway braces. A temporary repair was completed on the member and the structure was opened to one lane of alternating traffic. A detailed inspection resulted in such a low sufficiency rating that the structure became the highest-priority replacement need in the state. In December 2014, a temporary detour and crossing of the Dolores River was constructed. The structure was taken out of service with the completion of the detour.

Replacement

From fall 2015 through 2016, the U.S. Army Corps of Engineers (USACE) and CDOT evaluated the bridge as part of Section 106 of the National Historic Preservation Act, a federal law that requires federal agencies to take into account the effects of projects on historic properties. As part of that process, CDOT evaluated whether the bridge could be rehabilitated and left in place, but ultimately determined that it needed to be replaced with a new structure at the same location. 

As mitigation for the bridge removal, CDOT completed a National Park Service Historic American Engineering Record (HAER) documentation, which includes archival photos and a detailed narrative of the bridge's history. The bridge was also the subject of high-resolution LIDAR three dimensional scanning so that its structure type can be studied long after its removal. CDOT also made the progressive decision to store the bridge truss for future use, an approach to historic bridge preservation that has been considered but not carried out by the agency before.

In March 2017, the truss was moved off its abutments, disassembled and moved to a storage facility where it will remain until it can be reassembled in a new location. CDOT hopes the bridge will one day be re-purposed for use on a pedestrian/recreational trail so that people can appreciate an historically significant bridge type that is very quickly disappearing from the transportation landscape in Colorado.

Sources:

Blackwell, Chad, et al. Draft Historic American Engineer Record. Dolores River Bridge, HAER No. CO-102. 2016.

Fraser, Clayton. Colorado Historic Bridge Inventory. Historic Bridge Inventory Form. Dolores River Bridge (5MN4955). 2000.
Mead & Hunt Inc./Dill Historians LLC. Colorado Historic Highway Inventory—Historical Summary and Evaluation of Significance. State Highway (SH) 90. 2016.