IH-39/90 Reconstruction and Expansion North Segment

Challenge

The I-39/90 corridor, stretching from the Illinois state line to Madison, Wisconsin, was struggling with growing traffic, outdated design, and safety issues. A key point along this corridor, the US 12/18 Beltline Interchange, experienced severe congestion and operational challenges, directly impacting the flow and efficiency of I-39/90. To address these issues, WisDOT launched a 45-mile reconstruction and expansion project aimed at modernizing the corridor, enhancing safety, and preparing for future growth. 

Solution

SEH, in collaboration with a joint-venture team of leading engineering firms, helped reconstruct nine miles of freeway in Dane County, Wisconsin, expanding the roadway from four to six lanes. Work included bridge reconstruction and replacements, new service roads, drainage systems, signing, pavement marking, lighting, and landscaping. These improvements provided a modern corridor built to handle current and future traffic demands.

Interchange and Safety Improvements

Building on the expanded and modernized freeway, attention then turned to the Beltline Interchange and surrounding connections to further improve safety, traffic flow, and overall corridor efficiency. The design and operational analyses led to the addition of a southbound lane at the exit to westbound US 12/18 and a third lane through the interchange core. These upgrades eliminated the “either/or” exit lane, a lane at freeway or expressway splits that lets drivers either exit or continue straight. Removing it simplified decisions, made driver movements more predictable, and reduced conflicts with through traffic.

Traffic Operations and Environmental Coordination

With the interchange and safety improvements in place, the project then focused on optimizing traffic operations and coordinating environmental requirements to ensure the corridor functioned efficiently and met regulatory standards. The team prepared operational and safety analyses for corridor interchanges, including Intersection Control Evaluations at two locations. These studies compared traffic control options and guided preferred designs. At the same time, the team worked closely with federal agencies to transition environmental documentation from an Environmental Impact Statement to an Environmental Assessment, streamlining approvals while maintaining compliance.

Public Involvement and Construction Staging

Community engagement played a major role. SEH led an intensive public involvement process, including newsletters and gathering feedback that directly shaped the final design. To keep traffic moving during construction, the team also developed detailed staging plans that used temporary roadways, median crossovers, and detour routes, minimizing disruption for commuters and freight traffic.

The completed project improved travel times, reduced congestion, and created a safer driving experience for thousands of daily users. Drivers now benefit from smoother mergers and exits, while the region enjoys stronger connectivity and long-term mobility.