I-5 - Tumwater to Mounts Road Corridor Planning and Environmental Linkages 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

Planning and Environmental Linkages

WSDOT is building upon the goals and strategies outlined in the corridor study developing a "Planning and 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. The PEL process outlines a collaborative and integrated approach to transportation decision-making incorporating community, economic, and environmental goals into WSDOT's practical solutions requirements. In the PEL study, WSDOT is analyzing the strategies for environmental constraints; working with TRPC's traffic modeling team to determine each individual strategy's benefits to the transportation system; and seeking affordable strategies easily implemented that improve person throughput. In spring 2021, the PEL team will reconvene the stakeholder committee, working with the Tribes, resource agencies, and citizens to obtain their input. There is currently no funding identified to implement the strategies in this study.


Spring - Fall 2020

  • Develop PEL Study Schedule
  • Group strategies for traffic modeling
  • Environmental background and data collection
  • Determine stakeholder groups

Winter 2020 - 2021

  • Traffic modeling
  • Data collection
  • Finalize outreach plan
  • Tribal notification

Spring - Fall 2021

  • Using traffic modeling, prioritize individual strategies
  • Meetings with Stakeholders, Tribes, Environmental agencies, and the public
  • Draft report for review and comment
  • Finalize report

Other Documents

I-5 Tumwater to Mounts Road Mid- and Long-Range Strategies Corridor 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)

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. 


Dennis Engel, Multimodal Planning Manager

Theresa Turpin, Multimodal Development Manager