Interstate 80 (I-80) is a bustling east-to-west transcontinental highway that runs from San Francisco, California, to Teaneck, New Jersey. In between, it stretches through the heart of Iowa and carries ever-increasing traffic loads as well as large oversize, overweight freight and shipping trucks.

Near Iowa City on the eastern side of the state, I-80 intersects with Herbert Hoover Highway – a 42-mile roadway that pays tribute to the Iowa-born U.S. president. In the 11.2-mile stretch between Iowa City and West Branch, average daily traffic volumes reach up to 35,000 vehicles per day, 35 percent of which is large truck traffic. Numbers are only expected to rise. Safety had become a growing concern as well, with a noticeable uptick in traffic slowdowns and crashes.

Interchange prior to construction.

For over a decade, the Iowa DOT recognized the need and was working to make large-scale improvements to accommodate the steady increase in capacity and boost driver safety. Project goals included widening I-80 from four to six lanes in each direction and making upgrades to the interchange at Herbert Hoover Highway. Through the Iowa DOT Roundabout Review Master Contract, MSA was asked to provide an alternative at this interchange and evaluate if a dual roundabout option at the ramp terminals would be viable. MSA determined that roundabouts would safely, efficiently, and cost-effectively move traffic at the location.

MSA was then contracted to assist the department with design, plans, and specifications for this alternative interchange. The implementation of roundabouts at the ramp terminals would allow for a lower design speed through the I-80 crossing and support a significantly reduced skew in the roadway. In addition to the dual roundabouts, a new overpass bridge that crosses I-80 at the ramp terminals was designed. Because of the selected roundabouts and subsequent lowering of vehicular speed throughout the area, the bridge cross-section was able to be narrower, saving the department significant project costs.

Constructed in 2021-2022, MSA’s design of tandem roundabouts is already proving to lower vehicular crossing speeds, deliver efficiency at the ramp terminals, and further calm traffic due to the narrow overpass bridge. The project required close coordination and construction staging with the Iowa DOT, Johnson County, and other project stakeholders. The result is the first roundabout interchange on I-80 in the state of Iowa.

Dual-roundabout interchange after construction.