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Diverging Diamond Interchange Relieves Congestion in Coralville

Coralville, IA

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 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.

The City of Coralville hired HR Green to design the DDI interchange and evaluate grade-separated trail alignments to keep pedestrians separate from the vehicular traffic through the interchange. HR Green developed 12 different trail alignments and coordinated with the emergency services, the bicycle coalition, different city departments, and the Iowa DOT to determine an alignment that would work given the challenging grades in the area.

Coralville Diverging Diamond Interchange

The Diverging Diamond Interchange at 1-80 and 1st street in Coralville reduces congestion and improves safety.

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.

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