Corven Engineering, a Hardesty & Hanover company, was the Bridge Designer and Engineer of Record for the widening of the Vista Avenue Bridge Interchange. The Interchange crosses Interstate 84 in Boise, Idaho, providing access to Boise Airport. The widening of I-84 required that the existing diamond interchange be completely replaced with a new Single Point Urban Interchange (SPUI).
With the importance of access to the airport, the Idaho Transportation Department stipulated that the construction impact should be minimized using Accelerated Bridge Construction (ABC) techniques. The interchange has two 90 foot spans comprised of Type IV AASHTO girders and a cast-in-place reinforced concrete deck. The width of the bridge is 197 feet to accommodate the SPUI configuration. The new bridge was designed to be built using self-propelled modular transporters (SPMT). The superstructure was built adjacent to the site in four full-span, half-width quadrants and then transported to the final location along the new bridge alignment. Closure pours tie the four pieces together.
During construction, the contractor proposed, and the DOT accepted a change to more conventional construction for the superstructure while keeping other ABC aspects of the project. Cast-in-place footings, abutment walls, and piers stems were constructed beneath and beside the existing bridge without interrupting traffic. Abutment seats and pier caps were precast and erected on the cast-in-place elements to speed construction. Half of the new bridge was erected adjacent to the existing bridge. Traffic was then shifted from the existing bridge to the completed portion of the new bridge, and the remainder of the bridge was constructed. Corven also provided engineering support during construction.