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SR 509, I-5 to 24th Avenue S. – New Expressway Project – Key Feature: SR 509 I-5 Expressway and ramps

SR 509 I-5 Expressway and ramps

The following section describes some of the key features of the project. The designs presented are conceptual. The design-builder will finalize the schedules and designs, which may vary from the conceptual designs.

Building the first mile of the SR 509 Expressway and the ramps that will connect I-5 to the SR 509 will require major construction in SeaTac. WSDOT’s contractor will:

  • Build the first mile of the SR 509 Expressway between 24th Avenue South and I-5 and the electronic toll point (near South 210th Street).
  • Build a new I-5 overpass near South 212th Street. The overpass will connect northbound I-5 to northbound SR 509.
  • Build a new southbound I-5 off-ramp just south of Military Road South
  • Build a new southbound SR 509 ramp that will connect southbound SR 509 to southbound I-5.
  • Connect the new ramps to Veterans Drive and the SR 516 interchange
An aerial image of the new I-5 expressway and ramps
A reconfigured SR 516 interchange, new ramps that provide connections between SR 509 and I-5, and non-motorized improvements will make it easier for people who drive, walk, bike and use transit to travel through the area.

Construction impacts:

Our contractor will develop specific plans for constructing the northbound SR 509 overpass. However, their plans to build an overpass instead of an underpass  reduces impacts to the traveling public. The overpass eliminates the need for I-5 closures and lane shifts that were part of the original designs, which included building I-5 bridges that the new SR 509 would travel under. More specific information about overpass construction will be provided at a construction open house in late 2021 or early 2022.

This artist’s rendering shows how the northbound SR 509 ramp goes over I-5. This design greatly reduces impacts to I-5. In the original design, the ramp went under I-5, which required extensive, long-term traffic shifts during construction.

Please share any questions or comments on this part of the project on the comments and survey page.