Skip to main content

I-5 Tumwater to Mounts Road Corridor Planning and Environmental Linkages Study – Widen/Add Capacity Strategies Moving Forward

Maps and figures are conceptual and not to scale.

Map legend
Strategy #StrategyDescriptionMilepost
Cap 4.1Widen, Add Capacity US 101 Interchange to Pacific Ave SE InterchangePortions are already four lanes; add a lane where there are only three lanes, with the HOV lane as the inside lane both directions I-5 from Pacific Ave SE interchange to US 101 interchange.104.3-107.1
Cap 4.2Widen, Add Capacity Pacific Ave SE Interchange to Martin Rd NE InterchangePortions are already four lanes; add a lane where there are only three lanes, with the HOV lane as the inside lane both directions I-5 from Marvin Rd NE interchange to Pacific Ave SE interchange.107.-111.7
Cap 4.3Widen, Add Capacity Marvin Rd NE Interchange to Mounts RdWiden I-5, add capacity by adding one HOV lane and maintaining the three existing general purpose lanes, and provide multimodal accommodations.111.7-117.0
Cap 5I-5 Southbound- Pacific Ave to Plum St off rampAdd an auxiliary lane between Pacific Avenue and Capitol Way.106.1-107.2
Cap 6I-5 Northbound US 101 on ramp to Pacific Ave off ramp Add an auxiliary lane from US 101 on ramp to 14th Avenue off ramp, and from Plum Street on ramp to Pacific Avenue off ramp.104.6-107.1
Cap 7I-5 Northbound at US 101- flyover rampAdd a flyover off ramp linking NB I-5 to WB US 101, and merging in on the outside lane of US 101. Retain the Deschutes Parkway on ramp to provide access from the local network to US 101.104.1-104.4; 366.9-367.3

Cap 4.1: Widen, Add Capacity US 101 Interchange to Pacific Avenue Southeast Interchange

  • Portions are already four lanes; add a lane where there are only three lanes, with the HOV lane as the inside lane both directions I-5 from Pacific Ave Southeast Interchange to US 101 interchange
  • Recommended to move forward due to increased volume and speed.

(Cap 4.1 and Cap 4.2 were modeled together, so see images under Cap 4.2)

Cap 4.2: Widen, Add Capacity Pacific Ave Southeast Interchange to Marvin Road Northeast Interchange

  • Portions are already four lanes, add a lane where there are only three lanes, with the HOV lane as the inside lane both directions I-5 from Marvin Rd NE interchange to Pacific Ave SE interchange
  • Recommended to move forward due to increased volume and speed.
Two side-by-side aerial photos of Interstate 5 show improvements to include adding a lane in places where there are only three lanes. Green is used to depict the HOV lane, which is the inside lane both directions.
Mounts Road Interchange connect SB HOV; Left: Existing. Right: Improvement. Green is HOV lane. Image from Thurston Regional Planning Council
Two side-by-side aerial photos of Interstate 5 show improvements to include adding a lane in places where there are only three lanes. Green is used to depict the HOV lane, which is the inside lane both directions.
Mounts Road Interchange connect NB HOV; Left: Existing. Right: Improvement. Green is HOV lane. Image from Thurston Regional Planning Council
Two side-by-side aerial photos of Interstate 5 show improvements to include adding a lane in places where there are only three lanes. Green is used to depict the HOV lane, which is the inside lane both directions.
Exit 104 off and on-ramp begin NB end SB HOV. Left: Existing. Right: Improvement. Green is HOV lane. Image from Thurston Regional Planning Council

Cap 4.3: Widen, Add Capacity Marvin Road Northeast Interchange to Mounts Road

  • Widen, add capacity Marvin Road Northeast Interchange to Mounts Road
  • Recommended moving forward due to increased volume and speed and improved climate change resiliency. Widening should accommodate multimodal opportunities.

Approaching Mounts Road Interchange

Existing. Green is HOV lane. Image from Thurston Regional Planning Council
Two side-by-side aerial photos of Interstate 5 show improvements to include adding a lane in places where there are only three lanes.  Green is used to depict the HOV lane, which is the inside lane both directions.
Improvement. Green is HOV lane. Image from Thurston Regional Planning Council

After Marvin Road Interchange

Existing. Green is HOV Lane. Image from Thurston Regional Planning Council
Two side-by-side aerial photos of Interstate 5 show improvements to include adding a lane in places where there are only three lanes.  Green is used to depict the HOV lane, which is the inside lane both directions.
Improvement. Green is HOV Lane. Image from Thurston Regional Planning Council

Cap 5: I-5 Southbound – Pacific Ave to Plum Street Off-Ramp

  • Add an auxiliary lane between Pacific Avenue and Capitol Way
  • Recommended to move forward due to increased throughput on braided ramp section. Recommend further analysis with signage and redesign of Plum Street exit.
Two side-by-side aerial photos of an intersection show proposed improvements to include adding an auxiliary lane between Pacific Ave and Capitol Way
Left: Existing. Right: Improvement. Image from Thurston Regional Planning Council

Cap 6: I-5 Northbound US 101 on-ramp to Pacific Avenue off-ramp

  • Add an auxiliary lane from US 101 on-ramp to 14th Avenue off-ramp, and from Plum Street on-ramp to Pacific Avenue off-ramp.
  • Recommended to move forward due to increased speed and throughput.
Two side-by-side aerial photos of an intersection show proposed improvements to include adding an auxiliary lane from US 101 on-ramp to 14th Avenue off-ramp, and from Plum Street on-ramp to Pacific Avenue off-ramp
Start of auxiliary Lane NB after US 101 merge; Left: Existing. Right: Improvement. Image from Thurston Regional Planning Council
Two side-by-side aerial photos of an intersection show proposed improvements to include adding an auxiliary lane from US 101 on-ramp to 14th Avenue off-ramp, and from Plum Street on-ramp to Pacific Avenue off-ramp
Henderson Boulevard. Left: Existing. Right: Improvement. Image from Thurston Regional Planning Council
Two side-by-side aerial photos of an intersection show proposed improvements to include adding an auxiliary lane from US 101 on-ramp to 14th Avenue off-ramp, and from Plum Street on-ramp to Pacific Avenue off-ramp
End at Pacific off-ramp. Left: Existing. Right: Improvement. Image from Thurston Regional Planning Council

Cap 7: I-5 Northbound at US 101-Flyover Ramp

  • Add a flyover off-ramp linking northbound I-5 to westbound US 101 and merging in on the outside lane of US 101. Retain the Deschutes Parkway on-ramp to provide access from the local network to US 101.
  • Recommended to move forward due to increased throughput in northbound direction and reduced queue at exit.
Two side-by-side aerial photos of an intersection show proposed improvements to include adding a flyover off-ramp linking NB I-5 to WB US 101 and merging in on the outside lane of US 101.
NB Flyover near Custer Way. Left: Existing. Right: Improvement. Image from Thurston Regional Planning Council
Two side-by-side aerial photos of an intersection show proposed improvements to include adding a flyover off-ramp linking NB I-5 to WB US 101 and merging in on the outside lane of US 101.
Deschutes US 101 on-ramp. Left: Existing. Right: Improvement. Image from Thurston Regional Planning Council
Two side-by-side aerial photos of an intersection show proposed improvements to include adding a flyover off-ramp linking NB I-5 to WB US 101 and merging in on the outside lane of US 101.
Flyover ramp merge with mainline WB US 101; Left: Existing. Right: Improvement. Image from Thurston Regional Planning Council