I-5 - NB Seneca to SR 520 - Mobility Improvements

Project news

  • Work is scheduled to begin in spring 2021.
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Contractor crews will improve the mobility along a 2.51-mile stretch of northbound Interstate 5 from Yesler Way to Lakeview Boulevard through Seattle. Crews will:

  • Fill in a gap of about 1,500 feet where northbound I-5 reduces from three lanes to two, then expands back to three, between the Seneca Street off-ramp and the Olive Way off-ramp. This will create a continuous three-lane section in that area. To do this, crews will replace existing barriers, rails and curbs with a thinner barrier, reconstruct asphalt shoulders with concrete and restripe the roadway.
  • Install ramp meters on the collector-distributor on-ramp and the Cherry Street on-ramp.
  • Install nine new sign bridges, along with updated signing.
  • Extend Active Traffic and Demand Management (ATDM) system north to State Route 520.

Needs and benefits

This section of northbound I-5 carries approximately 100,000 vehicles a day and includes a two-lane section that creates one of the worst traffic bottlenecks in the state. Traffic often backs up to Boeing Field and there are many congestion-related collisions throughout the day.

Crews will rebuild the existing Seneca Street exit-only lane to add a third lane through the current two-lane bottleneck after the Seneca Street off-ramp. This third lane will be open to all vehicles and for those exiting at Seneca Street.

To create a seamless transition to the existing four lanes of traffic after the Cherry Street on-ramp, crews will add an auxiliary lane from the Cherry Street on-ramp, which will end as an exit only lane at Olive Way.

What should drivers expect?

To avoid disruption of the high daytime traffic volume on I-5, there will be mainly nighttime lane closures and flagging in the work zone.

The End Result

This mobility improvement work is projected to improve traffic flow and reduce congestion delays. High-occupancy vehicles will benefit with an additional bypass lane on the mainline and collector-distributor on-ramp. The extended ATDM system is expected to reduce collisions by providing drivers with information about what to expect as far as congestion and/or incidents ahead.

Needs & benefits

  • Improved safety: Extending the northbound I-5 ATDM system to SR 520 is expected to reduce collisions by adjusting speed limits based on conditions and providing drivers with information about what to expect as far as congestion and/or incidents ahead.
  • Congestion relief: Traffic flow through the area should improve and reduce congestion delays.


  • Fall 2020: Advertise for competitive bids
  • Spring 2021: Begin construction
  • Fall 2022: Complete construction


Financial Data for PIN 100521W, 100521X
Funding Source Amount ($ in thousands)
2003 Gas Tax (Nickel Funding) $0
2005 Gas Tax (TPA) $0
Pre-Existing Funds (PEF) $27,477
CWA $0
Total $27,477

This project received construction funding in the 2017-2019 transportation budget.

  • Planning and design ($2.77 million) were funded through a Puget Sound Regional Council (PSRC) grant and Pre-Existing Funds (PEF).
  • Construction ($17.74 million) was funded through federal and state Pre-Existing Funds.


Tom Pearce

A small map of the mobility improvements project is located along 2.51 miles of northbound I-5 from Yesler Way to Lakeview Boulevard East in Seattle.