The Interstate 5: Tumwater to Mounts Road Mid and Long-Range Planning Study (PDF 10.5MB) was conducted from 2018-2020. The corridor planning study was developed for the section of I-5 between 93rd Ave SW (SR 121) in Tumwater (Exit 99) and Mounts Road near DuPont (Exit 116), which experiences frequent congestion due to high traffic volumes and weaving at interchanges. Three locations experience recurring congestion during peak commute periods, including locations near the Nisqually River bridges (WSDOT 2020). This section of I-5 passes through the Nisqually River valley, an environmentally sensitive and important area for Endangered Species Act listed steelhead, and the traditional home of the Nisqually Indian Tribe. Recommendations identified in the study’s Next Steps included:
- Prepare for federal documentation requirements with a Planning and Environmental Linkages Study.
- Work with the Nisqually Indian Tribe to analyze hydrologic study results and develop recommendations.
A Planning and Environmental Linkages (PEL) process was developed from 2020-2022 to refine the information provided by the corridor planning study. The study area for the PEL (PDF 31MB) was I-5 from Tumwater (Exit 99) to Mounts Road (Exit 116). The corridor PEL identified strategies for regional congestion management, logical sections of the corridor to study further, and a strategic plan for the Nisqually River bridges that considers ecosystem benefits to the Nisqually River estuary for salmon productivity and flood control. The corridor PEL recommended two improvements for the Marvin Road (Exit 111) to Mounts Road (Exit 116) section—adding a lane to the northbound I-5 on-ramp at the Nisqually Cutoff Road/Martin Way E interchange and adding one lane in each direction to I-5 from Marvin Road to Mounts Road (WSDOT 2022b). This focused PEL will document a more detailed alternatives development and evaluation process for the Marvin Road (Exit 111) to Mounts Road (Exit 116) section (Figure 1). After completing the focused PEL, this section will move directly into the NEPA environmental documentation phase to implement the I-5 capacity and Nisqually Delta environmental habitat restoration improvements.