I-39/90 and US 12/18 Madison Beltline Interchange

Challenge

The I-39/90 corridor in south-central Wisconsin is a vital transportation route that connects the Illinois state line and the US 12/18 Beltline in the City of Madison. However, this 45-mile section required expansion due to rising traffic volumes and safety concerns, necessitating a third lane in each direction to form a six-lane divided highway. Reconstruction of the existing lanes was essential, and outdated interchanges and grade-separated crossings were major contributors to the capacity limitations and safety issues that needed to be addressed.

The primary challenge of the I-39/90 and US 12/18 Beltline Interchange project was to address these deficiencies comprehensively. The project needed to accommodate high traffic levels, improve safety, enhance traffic operations at the interchange, and ensure compatibility with the broader I-39/90 expansion project to the south.  

Solution

SEH, in collaboration with a joint-venture team of leading engineering firms, played a pivotal role in addressing the challenges of this major infrastructure project. The team's responsibilities included design management, environmental documentation, and public involvement, among other essential services.

Initially, the project required an Environmental Impact Statement (EIS), but after two years of extensive study and federal agency coordination, a strategic decision was made to shift to an Environmental Assessment (EA). This change streamlined the regulatory process while still addressing all necessary environmental concerns.  As the project moved forward, public involvement became a key focus. A public hearing was held to gather feedback and address concerns, ensuring community input was integrated into the project. Extensive coordination was required with key stakeholders, including the Ho-Chunk Nation, Federal Highway Administration (FHWA), Dane County, the City of Madison, and the Town of Cottage Grove.

Prioritizing Safety

A vital aspect of the project was prioritizing safety within the interchange's area of influence. The team focused on cost-effective solutions that would significantly impact I-39/90's safety and traffic flow. Through an intensive but productive process, an option that included the addition of a lane along southbound I-39/90 at the exit ramp to westbound US 12/18 and a third lane through the interchange's core was selected. This expansion increased the roadway from three lanes to five, eliminating the problematic either/or lane at the exit ramp and providing much needed additional capacity. The result was a safer and more efficient exit maneuver for drivers that improved traffic flow through the interchange.

Performance-Based Practical Design

The project also incorporated performance-based practical design (PBPD), which is a quantitative decision-making approach that improves system performance throughout project development, to achieve the following benefits:

• Reduce impacts on the environment and surrounding communities
• Identify the greatest overall potential for safety improvements
• Enable an estimated $200 million in construction cost savings by utilizing the remaining life of the existing infrastructure

The completed project has transformed the I-39/90 and US 12/18 Beltline Interchange for the better. Drivers now experience a more comfortable and safer exiting maneuver with minimal impact on the adjacent free-flow traffic. This enhancement not only improves daily commutes but also contributes to the overall safety and efficiency of the regional transportation network.

Awards

• 2023 State Finalist Award | American Council of Engineering Companies, Wisconsin Chapter (ACEC-WI)