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

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The Washington State Department of Transportation is continuing its study of the Interstate 5 (I-5) corridor from Tumwater to Mounts Road. On this page, you will find information about previous and current I-5 studies. You will also find information on the strategies under WSDOT’s consideration. You will also have the opportunity to provide comment on the Planning and Environmental Linkages (PEL) Study and the strategies proposed for elimination and continuation.

Interstate 5 (I-5) crosses the Nisqually River delta amidst a natural landscape of wetlands, stream channels, and forest.
Photo credit: Washington State Department of Ecology Coastal Atlas

Study Overview

In 2018, the Washington State Legislature funded a corridor planning study of Interstate 5 between SR 121 in Tumwater (Exit 99) and Mounts Road near DuPont (Exit 116). The goal was to develop mid- and long-term strategies to improve the region’s transportation system. From 2018 to 2020, WSDOT and the Thurston Regional Planning Council (TRPC) completed the I-5: Tumwater to Mounts Road Mid- and Long-Range Strategies (Corridor Study). The Corridor Study included extensive public outreach and stakeholder coordination. More information on the Corridor Study is available here: Corridor Study Story Map

In 2020, WSDOT began work on the Interstate 5 (I-5) Tumwater to Mounts Road Planning and Environmental Linkages (PEL) Study. This is a continuation of the Corridor Study. As part of the PEL study, WSDOT held a stakeholder meeting on May 25, 2021. It included representatives from local governments, community groups, and Tribes. The PEL Study is underway, to be complete in the winter of 2021-2022.

Study Summary

The Corridor Study developed several goals for I-5: to relieve traffic congestion, and improve efficiency, equity, accessibility, environmental conditions, and resiliency. The study then reviewed over 140 suggested strategies for these goals. Eventually, 30 strategies were selected for evaluation in the PEL study.

The PEL Study included traffic modeling and preliminary environmental screening. This process removed strategies that did not contribute to the I-5 goals.

Each strategy reviewed fell under one of five categories for improvement:

  • Operations
  • Part Time Shoulder Use
  • HOV Conversion
  • Interchange Improvements
  • Widening/Add Capacity

During the PEL Study, 15 of the 30 strategies were eliminated. The rest moved forward to the National Environment Policy Act (NEPA) process.

Environmental screening identified the Nisqually Delta and the Deschutes River Estuary/Capitol Lake as two areas of concern. Strategies affecting these areas need more complex documentation and permitting. Screening also revealed that federally protected species and habitats may be present. There are also water crossing that will need fish passages.

The following describes the relationship between the Corridor Study, PEL Study, and future NEPA process:

Corridor study

  • Incorporated stakeholder, partner and public input
  • Developed & ranked goals & performance measures
  • Developed many strategies; screened for feasibility
  • Categorized strategies into like scenarios
  • Ranked the scenarios based on effectiveness toward goals

Leads into:


  • Continued stakeholder, partner and public coordination/outreach
  • Traffic modeling of strategies
  • Preliminary environmental screening of strategies
  • Preliminary outreach to regulatory agencies
  • Recommended strategies to move forward into NEPA review

Leads into:


  • Review to determine level of NEPA analysis required
  • Emphasize strategies that will require EA/EIS
  • Conceptual project development
  • Environmental discipline reports
  • Continued coordination with partners and regulatory agencies


The following map shows strategies recommended to move forward to the NEPA process. The numbers on the map correspond with the strategies in the next graphic. As you can see, most strategies are on or near I-5. Some are farther away to improve resiliency in case of an unforeseen incident. Keep in mind that many strategies can move forward at once. Some are easier to implement than others as some need more complex design and permitting. Several strategies include improving multimodal accommodations.

Map of Strategies Moving Forward

A map of Washington State in the Olympia vicinity showing major towns, roads, and rivers with the approximate locations of fifteen transportation strategies depicted using points, lines, and arrows

Click the links below for more information on each strategy:



Widen/Add Capacity


The legislature allocated funding for the PEL study in 2020. Funding was also allocated to move the PEL strategies into the NEPA process.


  • Spring-Fall 2020
    Develop Schedule
    Group strategies for traffic modeling
    Begin environmental screening
    Identify stakeholders
  • Winter 2020-2021
    Traffic modeling
    Data collection
    Finalize outreach plan
    Tribal and stakeholder notification
  • Spring-Fall 2021
    Finalize modeling
    Evaluate strategy effectiveness
    Recommend strategies for elimination and continuation
    Coordinate with stakeholders, Tribes, agencies, and the public
    Draft report for review and comment
  • Winter 2021-2022
    Distribute draft report to Tribes and stakeholders for comment
    Public online open house
    Finalize PEL report

Next Steps

WSDOT is moving forward with hiring a consultant to begin NEPA work on strategy reviews. Public comments will get matched to the strategy to which they apply. The NEPA process will include reviewing public comments. Strategies will move forward based on funding.

Share your thoughts with us!


Dennis Engel, P.E.
Multimodal Planning Manager

Theresa Turpin, AICP
Multimodal Development Manager, Study Lead