I-5 - Tumwater to Mounts Road Corridor Study

I-5 Tumwater to Mounts Road Study Area Map

In 2018, the Washington State Legislature funded a planning study of Interstate 5 between SR 121 in Tumwater (Exit 99) and Mounts Road near DuPont (Exit 116) to develop mid- and long-term strategies for improving the region's transportation system performance. Collaborating with local partners, WSDOT and Thurston Regional Planning Council (TRPC) developed strategies to meet study goals and support local agency plans while focusing on the legislative requirements:

  • Identify strategies for regional congestion management
  • Identify potential improvements for the US 101/I-5 Interchange
  • Identify a strategic plan for the Nisqually River bridges that considers ecosystem benefits

Study Report

Executive Summary (pdf 1.8 mb)

Chapter 1 - Introduction (pdf 947 kb)

Chapter 2 - Related Studies and Planning Efforts (pdf 194 kb)

Chapter 3 - Study Process (pdf 555 kb)

Chapter 4 - Existing Conditions (pdf 1 mb)

Chapter 5 - Developing a Strategic Plan for Interstate 5 through the Nisqually River Valley (pdf 646 kb)

Chapter 6 - Modeling and Strategy Development (pdf 1.3 mb)

Chapter 7 - Strategy Evaluation and Modeling Results (pdf 626 kb)

Chapter 8 - Provisional Study Recommendations and Next Steps (pdf 568 kb)

Other Documents

The online open house (interactive map) provides information about the study and draft results. WSDOT held two in-person open house meetings in January 2020 in Olympia and Lacey. 

The survey results (pdf 355 kb) provide summary information about the two surveys. WSDOT received and reviewed roughly 4,600 responses to the surveys in total which included roughly 6,500 open-ended responses.

Next Steps

WSDOT will build upon the goals and strategies developed in this study to develop a "Planning & Environmental Linkages" (PEL) study. PEL represents a collaborative and integrated approach to transportation decision-making that 1) considers environmental, community, and economic goals early in the transportation planning process, and 2) uses the information, analysis, and products developed during planning to inform the environmental review process. In the PEL study, WSDOT will develop a more in depth analysis of individual components of recommended scenarios to evaluate which improvements provide the most benefit to the transportation system. There is currently no funding identified to fund the implementation of the strategies in this study.


Dennis Engel, Multimodal Planning Manager

Karen Parkhurst, TRPC Programs & Policy Director