Coralville Diverging Diamond Interchange Relieves Congestion

The City of Coralville and Iowa DOT have partnered to improve the I-80 and 1st Avenue Interchange. The Coralville Diverging Diamond Interchange (DDI), replacing the existing diamond interchange, is designed 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 through the interchange accessing the Iowa River Landing (IRL) and 1st Avenue than other interchange configurations.

This interchange is the gateway to the City of Coralville’s actively developing business and entertainment districts called the Iowa River Landing (IRL). The IRL is 180 acres of mixed-use land located in the southeast quadrant of I-80 and 1st 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.

HR Green was hired to design the Coralville Diverging Diamond Interchange and evaluate grade-separated trail alignments to provide safe, direct connectivity for pedestrians through the interchange and across the Interstate to the multi-modal center and the various services and amenities at the IRL.  HR Green evaluated 12 different trail alignments and collaborated with emergency services, bicycle coalition, city departments, and the Iowa DOT to determine an alignment that addressed the challenging topography and met the needs of various community interests.

The design of the project 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 11th 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 1st Avenue master plan.