I-5 Marvin Rd to Mounts Rd Planning and Environmental Linkage/NEPA

Project overview

This project began with a federal Planning and Environmental Linkages (PEL) study focused on Interstate 5 from Marvin Road to Mounts Road. The PEL considered additional technical analyses and stakeholder input to arrive at a final purpose and need and recommended alternatives to study in the environmental review phase. WSDOT initiated the National Environmental Policy Act environmental review, studying I-5 from Marvin Road (Exit 111) to Mounts Road (Exit 116) in summer 2024.

Funding is provided to accelerate work along I-5 through the Nisqually River Delta for preliminary engineering, design and right of way acquisition to address flood risk, improve mobility through the corridor between Mounts and Marvin Roads, and enhance the ecosystem at the I-5 Nisqually Delta crossing.

This page serves as the landing point for a potential future project. There is no construction planned at this time and traffic is not affected in this area.

What to expect

The National Environmental Policy Act (NEPA) environmental review process is underway. This allows project decision makers, resource agencies, and the public to understand the effects of the project on the built and natural environments. The environmental review will study a 4.7 mile stretch of I-5 between Marvin Road and Mounts Road interchanges. 

The final PEL Report (PDF 4.8MB) is available. You can also find the report and the appendices under the History and Background tab. You can also find answers to our frequently asked questions (PDF 251KB), which is also under the History and Background tab.

The primary improvements proposed with the project include:

• Widen I-5 by adding one high-occupancy vehicle lane in each direction from approximately Marvin Road in Thurston County to Mounts Road in Pierce County.
• Replace existing bridges and construct new bridges across the Nisqually Delta to increase the resiliency of I-5 to flooding and sea level rise and to support habitat enhancements in the delta.
• Construct a new grade-separated crossing of the BNSF Railroad east of the Nisqually River.
• Realign McAllister Creek where it crosses I-5 to improve tidal exchange, water quality and fish habitat.
• Build a shared-use path adjacent to I-5, providing a nonmotorized connection between Lacey and DuPont, and improve access to the Billy Frank Jr. Nisqually National Wildlife Refuge.
• Remove two exiting fish passage barriers under I-5 in the Red Salmon Creek drainage.
• Install new storm water treatment areas to treat runoff from I-5 within the project.
• Improve the surrounding habitat and allow for the creation of new habitat in areas where the existing I-5 embankment would be remove.

The NEPA environmental review started July 2024. A draft NEPA report is scheduled to be available in summer 2025. The final environmental assessment is expected to be finished in 2026.