Re-BUILDing Coralville’s 1st Avenue Interchange

The City of Coralville and Iowa DOT have partnered to improve the I-80 and 1st Avenue Interchange.  The existing diamond interchange will be replaced with a Diverging Diamond Interchange (DDI) design to handle projected traffic volumes.  One of the biggest safety and congestion issues is tied to the future number of left turns at the interchange.  The DDI is designed to accommodate the higher volume accessing the 1^st Avenue corridor than other interchange configurations.

The City of Coralville’s Iowa River Landing (IRL), once known as the Old Industrial Park, had fallen into neglect after the closure of local industries. The City saw this area as an opportunity to revitalize a very prominent and valuable tract of land with valuable access to Interstate 80 and 1^st Avenue.

Today, the IRL is the gateway to the City of Coralville’s actively developing business and entertainment districts. The IRL is 180 acres of mixed-use land located in the southeast quadrant of I-80 and 1^st Avenue.  It is home to the newly constructed University of Iowa’s Hospital and Clinics, a 6,000-seat arena and field house, a hotel conference center, a multi-modal transportation facility, and numerous shops and restaurants with the potential for more development to occur in the next 10-20 years.

The City of Coralville began the planning of the IRL project with a District Master Plan.  The plan featured the Hotel/Conference Center, Intermodal Transit Facility, a major attraction type land use, and a mix of office, retail, and residential land uses. The new use of land required a traffic impact study that analyzed the potential traffic impact of the development on the local roadway system.

The traffic impact study examined the individual land uses and evaluated existing traffic, projected traffic, projected land uses, peak hour traffic, roadway performance, and roadway capacity requirements for opening day and future conditions. The results of the traffic impact study led to additional studies to identify alternatives for adding capacity to the I-80/1^st Avenue interchange.

An Interchange Justification Report (IJR) and Categorical Exclusion (CE) were completed in 2010 and reevaluated in 2017 resulting in the DDI being the preferred alternative being carried forward into the design process.  Since the release of the draft IJR in 2010, the diverging diamond interchange (DDI) configuration has gained prominence across the United States with several being constructed each year.

The City of Coralville received notification in September 2020 that the project was the recipient of a $20.5 million federal grant from the U.S. Department of Transportation’s “Better Utilizing Investment to Leverage Development” (BUILD) program.  This means that Coralville now is fully funded to construct the proposed DDI interchange. The grant covers half the $41 million cost.  The other half of the funds are programmed in the Iowa DOT’s five-year plan.

The design of the DDI includes a unique grade-separated pedestrian trail, underpasses, and a trail bridge over I-80.  The project also includes parallel acceleration and deceleration lanes on I-80 and accommodates the potential future widening of I-80.  Due to the complex staging of the interchange and the need to maintain at least two lanes of traffic on I-80 during daytime hours, this design includes the construction of two independent bridge structures to replace the existing bridges over I-80 in addition to the pedestrian bridge.  The design also includes an intersection at 11^th Street/Iowa River Landing Place, retaining walls, storm sewers, ditching/ culverts, traffic signals, and pedestrian underpasses.  Aesthetic design elements are being incorporated to match the City of Coralville’s and Iowa DOT’s I-80 and 1^st Avenue master plan.