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Iowa DOT Nears Completion on New Interchange, Bringing Improved Traffic Flow and Safety to Growing Coralville

by: Larry Bernstein
The 1st Avenue and I-80 Interchange project will install a diverging diamond interchange to reduce traffic delays and improve safety.
The 1st Avenue and I-80 Interchange project will install a diverging diamond interchange to reduce traffic delays and improve safety.
Coralville, Iowa, is centrally located to various popular areas in the state, being 25 miles south of Cedar Rapids, just outside Iowa City, and close to the University of Iowa. The centrally located city is growing, and the Iowa Department of Transportation (Iowa DOT) along with Peterson Contractors Inc. (PCI), are working on a project to help facilitate better traffic flow in the area.
Bustling Area
The population of Coralville in 2023 was just over 23,000, and the city has been growing steadily. Nearby Iowa City has a population of over 75,000, and the University of Iowa has 33,000 students.

The project — 1st Avenue and I-80 Interchange — is taking place along one of the busiest interchanges in the area. The average daily traffic was 27,435 in 2021, and it is projected to reach 35,580 in 2045.

The need for a new interchange, however, is not new. “The Iowa DOT and the City of Coralville have been planning to modernize the I-80/1st Avenue Interchange in Coralville for many years,” said Adrian Simonson, the Resident Construction Engineer overseeing the project for Iowa DOT.

The Iowa River Landing (IRL), a 180-acre mixed-use development, is located near the project area. IRL includes a hospital associated with the university and Xtream Arena, which seats over 5,000. The area was once home to an industrial park, but the industries closed, and the space was vacant.

Magellan Midstream Partners, which transports, stores, and distributes refined petroleum products and crude oil, has a terminal near the project area. According to the company’s website, Magellan “owns the longest refined petroleum products pipeline system in the country” and is one of the largest employers in Coralville.

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Due to the IRL development and the potential for more growth, as well as other activity in the area, a traffic impact study was conducted. The current project (and others) originated because of the study findings.

The New Interchange
The project has a vast scope. However, the main element of the project is the installation of a diverging diamond interchange (DDI). Previously, the area had a conventional diamond interchange. The team is switching to a DDI, which eliminates left turns that cross the path of approaching vehicles at signalized intersections.

“This reduces overall traffic delays while also providing a significant safety improvement since left-turning traffic is no longer crossing opposing traffic lanes,” Simonson said. He added that the DDI was selected because it can “best handle the projected increased traffic volumes on the ramps and allows for future widening of I-80 due to its smaller footprint.”

In the past, there were back-ups on the interchange during peak morning and evening traffic times. To improve safety, 0.5-mile acceleration/deacceleration lanes are being added to the ramps west of the interchange.

The team is also installing new 1st Avenue bridges to accommodate the potential future widening of I-80. Two new traffic bridges (which are parallel) joined by median cab are being built. The six-lane bridge is being built to accommodate a future fourth lane in each direction.

The scope also includes the installation of a new, signalized intersection to serve Iowa River Landing and the Magellan Terminal.

Coralville has an extensive trail system, and many people bike or walk to work. According to Simonson, the city wanted to develop the trail system further, so they incorporated trail improvements into the project.

The team is installing a new grade-separated trail with underpasses and a trail bridge over I-80. The full grade separated (requiring the installation of three pedestrian box culverts) will take the trail under the IRL, eastbound ramp, and bridge over I-80 in the direction of east to west.

“The work on the trail means pedestrians will never have to cross the traffic, as opposed to before when they had to cross the ramps,” Simonson said. “It was a safety hazard.”

Finally, the scope included new stormwater management practices, traffic signals, roadway lighting, and aesthetic treatments.

Soil and Spatial Challenges
This project required many geotechnical improvements: wick drains, intermediate foundation improvements, core outs, and light weight foamed concrete fill.

“We installed wick drains to allow water to flow up as the ground was compressed,” Simonson said. The team also installed seven mechanically stabilized earth retaining walls — a total of 40,000 square feet.

Forty-five feet below the interstate, there was a 300-linear-foot 60-inch trenchless RCP culvert that had to be extended because of widening at the ramps west of the interchange. Doing so was costly in terms of time and money.

The foundation requirements were necessary due to the soils in the area.

Another challenge the team had was the limited space in which to work. They were only able to acquire a limited amount of right of way. “We have to work in quadrants of [the] interchange and are constantly juggling how to move around the stages,” Simonson said.

An additional related challenge is the fact that two lanes in each direction are required to be kept open. The limited times that the ramps could be closed (40 days throughout the contract) had to be scheduled around football season. Overall construction did not begin until after football season concluded. Message boards have been installed to help with traffic control.

Lastly, utility coordination has also been a challenge during the project. A significant amount of state fiber had to be moved. This was particularly sensitive because of the hospitals in the area. “We had to coordinate the cut over of the fiber line with multiple parties,” Simonson said.

Magellan has gas lines in the area, which are also highly sensitive.

Coordination and Expertise
Peterson Contractors Inc., which is headquartered about 90 miles from Coralville, is the general contractor. They have worked with Iowa DOT on many occasions all around the state.

The contractor was selected based on low bid. Their project management skills have been essential. “This project has multiple elements, requires lots of subcontractors, and is staged as such that it requires careful planning and coordination to stay on schedule,” Simonson said.

PCI has performed many Iowa DOT projects, but this is Simonson’s first time working with the contractor. “PCI has performed all work according to the contract, and we’ve been pleased with them,” Simonson said.

The project has a $37.4 million construction budget. Coralville received a $20.5 million federal BUILD Grant for the project, which is their contribution to the funding. The remaining construction funds are state highway funds.

“There have been some unforeseen field conditions and quantity adjustments that have resulted in project cost changes,” Simonson said. “However, Iowa DOT recognizes the possibilities of project risks and plans for them within our overall budget, and we remain on budget.”

Project construction began in the fall of 2022 and is on track to be substantially complete by the fall of 2024. Communication and coordination between the contractor, project team, city, and public have been the key to keeping the project on schedule.

Many things are going on in and around Coralville, leading to an increase in traffic. The 1st Avenue and I-80 Interchange project will decrease traffic delays and will accommodate the future I-80 widening, with no further disruption to 1st Avenue. Plus, bikers, hikers, and other users of the pedestrian trails will soon be able to enjoy a safer journey.

Project Partners/Personnel
  • Owner: Iowa Department of Transportation
  • General Contractor: Peterson Contractors Inc., Reinbeck, Iowa
  • Project Designer: HR Green, Cedar Rapids, Iowa
  • Project Engineer: Adrian Simonson, PE
  • Key Subcontractors: Iowa Bridge & Culvert (pedestrian box culvert construction); K & W Electric (traffic signals, lighting, and signing); Quality Traffic Control (traffic control and pavement markings); Rathje Construction (storm sewer and culverts); Streb Construction (PCC paving)
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