The Chubbuck Diverging Diamond Interchange, which connects U.S. 91/Yellowstone Highway over the Interstate 86 system in Chubbuck, Idaho, has received the Idaho Transportation Dept.’s 2014 Excellence in Transportation Award in the Large Design category.

ITD sponsors the Excellence in Transportation Awards to recognize outstanding initiatives in developing, planning and implementing transportation projects throughout the state.

The project replaced an existing bridge, provided increased capacity for the current interchange and increased safety. Engineering firm Parsons Brinckerhoff worked closely with ITD District 5 to lay the groundwork for this innovative freeway interchange solution.

PB provided preliminary engineering, which was then used to evaluate interchange types against a set of criteria that included cost, performance, right-of-way impacts, access impacts to existing businesses and other criteria.

The evaluation led to a recommendation to construct a diverging diamond interchange, which offers benefits compared to a traditional diamond interchange, the most significant of those being continuous left-turning traffic. Because traffic is crossed over to the opposite side of the bridge, there is no waiting for left turns to get onto the interstate. This eliminates a phase for the signals and reduces the potential for crashes with left-turning traffic.

Once ITD received permission to move the project forward, Parsons Brinckerhoff prepared an interchange access modification request for the Federal Highway Administration, as well as a noise study for the project area. ITD completed final design for the project, and construction was completed in 2013 on Idaho’s first diverging diamond interchange.