I-43 North-South Freeway

As one of Wisconsin’s busiest corridors, the Interstate 43 North-South Freeway serves as a vital interstate link connecting southeastern Wisconsin to the rest of the state. With traffic volumes projected to exceed 100,000 vehicles per day by 2045, the Wisconsin Department of Transportation (WisDOT) invested in a comprehensive modernization of the freeway to expand capacity, meet future demands and improve safety. 

Modernizing a corridor while maintaining connection

Spanning a total of 14 miles, the I-43 North-South Freeway project transforms one of the state’s busiest four-lane freeway into a modern, six-lane corridor. The project also included the reconstruction of five interchanges, addition of a diverging diamond interchange, replacement of a Union Pacific railroad bridge and five major box culvert crossings. 

HNTB partnered with WisDOT throughout the full lifecycle of the I-43 North-South Freeway project, delivering comprehensive services from early environmental documentation and preliminary engineering to final design, construction engineering and inspection, traffic management and public involvement. Through HNTB’s traffic management services, WisDOT kept all four lanes of the freeway open during construction and provided safe and reliable access to the corridor’s many businesses, schools and community institutions. 

Key corridor improvements include:

• Expanded capacity and structural upgrades, including 14 new bridges and 35 retaining walls
• Enhanced multimodal connectivity, with new bike lanes, a shared-use path and improved pedestrian access integrated into local road reconstructions
• Innovative interchange designs to improve traffic flow and safety, including the first diverging diamond interchange in southeast Wisconsin
• Improved stormwater management systems to enhance environmental resilience and roadway performance
• Noise mitigation features, including four miles of new noise retention walls
• Rail and roadway coordination, including a new Union Pacific Railroad bridge spanning multiple roadways to streamline freight and vehicle movement

HNTB worked closely with WisDOT, two counties and ten municipalities to deliver a corridor that reflects local priorities and long-term regional needs. Outreach efforts reached more than 21,000 stakeholders — including residents, businesses, elected officials, review agencies and Native American tribes — providing timely, accessible information during the project's delivery. 

The modernized I-43 North-South Freeway stands as a testament to thoughtful planning, collaborative execution and a shared vision for a safer, more connected Wisconsin.