3/21/2014
Replacement of bridges on Idaho 75 southwest of Challis starts in early April
RIGBY - Replacement of two bridges on Idaho 75 southwest of Challis will begin as early as Monday (April 7), the Idaho Transportation Department announced. The contractor will accelerate bridge construction by using preconstructed bridge sections in order to finish in November.
Crews will replace the bridge over the East Fork and the bridge over the main channel of the Salmon River on Idaho 75. Situated about 200 yards apart, these bridges form the East Fork Salmon River Bridge Complex (see photo), located 18 miles southwest of Challis, near milepost 227.
The contractor will maintain two-way travel on Idaho 75, with minimal disruptions. Crews will construct two temporary work bridges for cranes. As construction advances, ITD will notify the public of anticipated changes to traffic flow on Idaho 75.
During construction, motorists should watch for workers, equipment and traffic signs. Work may temporarily close boat accesses adjacent to and under the construction sites of the project, but boats may access the Salmon River near these construction sites. At times, crews may restrict boat travel through the channels, especially when setting girders.
Use of local river access points will be curtailed briefly during demolition of the old bridges this fall and perhaps a few times when the contractor needs to use the access points during construction this summer.
The Challis Bureau of Land Management decided to close its East Fork Campground, which lies between the bridges, after discussions with the transportation department and the contractor on the need for a work staging area at the campsite.
Built in 1938, the bridges have well exceeded their 50-year design life. The new bridges will be just east (upstream) of the existing ones, after which the old bridges will be removed. The project will include constructing approaches to the new bridges to improve traffic safety and flow.
Crews first will construct the temporary work bridges. New bridge and approach construction is scheduled for completion by Thanksgiving Day, with seal coating planned in 2015.
The transportation department awarded the $7.4 million contract to Knife River Corporation’s southern Idaho division, based in Boise.
The existing structures have National Bridge Inspection System sufficiency ratings of 61 and 44, respectively, out of a possible 100. A rating below 50 indicates the need for replacement. Both bridges are being replaced at the same time due to their proximity, similar construction and operational histories.
Width, load capacity and safety railing of the old bridges are substandard. The Salmon River Bridge also is susceptible to critical scour, or bridge erosion, during a 500-year storm event.