The I-80/I-35 to IA 141 flyover bridge is the cornerstone element to resolve congestion and safety challenges at the convergence of I-80 and I-35 with Iowa Highway 141 (locally known as Rider Corner and now known as the Urban Loop) in the Cities of Urbandale, Grimes, and Johnston in the northwestern quadrant of the Des Moines metro area. Not only is the flyover a critical element of the overall interchange design, but the planning and design of adjacent interchanges were needed to address several corridor constraints, multiple construction staging and safety challenges, geotechnical challenges, as well as accommodate a future collector-distributor concept parallel to the I-80/I-35 mainline.
Urban Loop Purpose
As the combined routes of I-80 and I-35 curve around the northwest quadrant of the Des Moines metro at the border between the cities of Urbandale and Grimes, the existing interchange with IA 141 featured a folded-diamond interchange, with an exit loop ramp where 90% of the exiting traffic continues north on IA 141, going through several traffic signals before leaving the interchange area. Traffic often backed up onto the Interstate in the northbound direction from the exit loop ramp, resulting in delays, congestion, and crashes. The City of Urbandale and other adjacent communities sought improved access to support and promote economic development.
Several solutions were studied over the years, ranging from improvements to the existing type of interchange to a complex systems interchange. These solutions either did not sufficiently solve the corridor challenges or were too expensive with significant impacts on surrounding land use.
Improved Safety and Access
The design process started with the flyover concept to solve the most critical issue in the corridor, which was the exit loop ramp. “Right Sizing” the balance of the solution through context-sensitive design led to the flyover concept along with adding a partial interchange to the south at Meredith Drive and a full interchange to the east at 100th Street.
The ten piers were located to allow the bridge to span over I-35/I-80 without a pier in the median and to span across IA 141, the railroad, and existing ramps with minimal traffic restrictions during construction. In addition, the piers were located to accommodate the construction of future lanes. The flyover bridge took just under two years to complete and included the development of aesthetic features to complement other bridge projects in the corridor as well as retaining walls, Intelligent Transportation System accommodation, signing, and continuous corridor lighting.
A final, or ultimate build, scenario was developed and approved by Federal Highway Administration (FHWA) to add collector-distributor roadways adjacent to I-80/I-35 mainline, connecting the added adjacent interchanges to provide long-term operational sustainability, enhancing system operations and performance as traffic patterns evolve and volumes build. 3D modeling was utilized to visualize the complex geometry interactions among the existing conditions, initial build, and ultimate build conditions. The 2020 construction implemented the initial build and with the completion of the project, there is a resurgence in economic development as the project brings improved safety and access to the corridor.
