The Topaz Bridge Redesign on U.S. Route 30

The Topaz Bridge is located in eastern Idaho on U.S. Route 30 between Lava Hot Springs and McCammon. It spans over the Union Pacific Railroad and the Portnuef-Marsh Valley Canal. The existing five span truss-style bridge is structurally deficient and functionally obsolete due to heavy traffic bypass. The replacement of the existing Topaz Bridge and its approaches are to be redesigned to better accommodate heavy commercial traffic, projected growth and overall safety. The chosen design features an expansion from two-lanes to four-lanes that will accommodate the 53% increase in daily traffic that is expected by 2024. The new steel-girder bridge will be designed taking into account clearance and easement requirements of the expanding Union Pacific Railroad that passes beneath the bridge. These requirements, along with poor soil conditions, require that the entire bridge rise vertically and extend from 319 feet to 616 feet long. Special consideration will be given to the Portnuef-Marsh Valley canal passing beneath the bridge when analyzing floodplains and designing storm-water collection. Overall, the new roadway approach and steel-girder bridge enhances vehicle capacity, accessibility, intermodal transportation, and safety of this section of U.S. Route 30