A major portion of the extension of State Route 509 from SeaTac to Interstate 5 near Kent remains in the design stage this year, but expect lots of construction to start in 2022 with an anticipated finish in 2025 for much of the work.
The project will include major changes in Kent to the State Route 516 interchange with I-5 and the extension of Veterans Drive from Military Road South underneath I-5.
It’s all part of an estimated $2 billion Puget Sound Gateway Program to improve connections to the Ports of Seattle and Tacoma and help ensure people and goods move more reliably through the region, according to the Washington State Department of Transportation (WSDOT).
Work already has started on the extension of State Route 167 from Puyallup to I-5 and the Port of Tacoma.
Next will come the work to build the SR 509 Expressway to add a southern access point to Sea-Tac Airport and improve service between industrial districts (Kent Valley) by allowing general purpose traffic and trucks to bypass I-5, State Route 99 (aka Pacific Highway South in Kent) and local streets.
Colorado-based Atkinson Construction, which has a Northwest Division office in Renton, will design and build the project.
“This second stage of construction for the SR 509 Completion Project is a design/build contract, which means the contractor, in this case Atkinson Construction, finalizes project design before construction starts,” said Laura Newborn, WSDOT communications manager, in an email. “Design work will take place through 2021, with construction expected to start in early 2022.”
Sound Transit is working with WSDOT on the first stage since the Federal Way light rail extension, under construction and scheduled to be completed in 2024, covers a similar path through some communities. That work has started and includes a new SR 99 bridge near South 208th Street. Light rail will go over the bridge and SR 509 under it.
The final 2 miles of the new SR 509 Expressway between 24th Avenue South and South 188th Street in SeaTac will be built under a separate contract, scheduled to be advertised in 2023 and completed in late 2028.
The changes in Kent are needed due to the high traffic volumes at the I-5/SR 516 interchange. People who use the interchange experience congestion on the ramps and at the traffic signals. WSDOT will make improvements to the I-5/SR 516 interchange to improve traffic flow, freight mobility, pedestrian and bicycle access and transit connections with light rail coming to the West Hill.
The improvements include:
• Reconstructing the ramps and adding lanes to improve traffic flow
• Constructing a new Veterans Drive undercrossing of I-5, connecting Veterans Drive to the southbound I-5 off-ramp and northbound on-ramp, creating a parallel roadway to SR 516 to improve traffic flow through the interchange
• Building wider sidewalks and a shared use path
Combined, these improvements will reduce delays at the interchange, connect trucks to the manufacturing and warehousing area in the Kent Valley and make it easier for people getting to transit without a car, according to WSDOT.
The interchange will remain open during most of the work, but state officials anticipate periodic ramp closures. In addition, to construct the Veterans Drive undercrossing, the contractor will need to shift and reduce the width of lanes on I-5 for an extended period.
When finished, SR 509 will be a key component of the Seattle and south King County transportation network, according to WSDOT. Along with the SR 99 tunnel improvements, the project provides a critical north-south alternative to I-5 through Seattle and King County.
The SR 509 Completion Project was originally funded over a 16-year timeline with targeted completion in 2031. The state Legislature advanced program funding in the 2019 session, moving project completion to 2028.
Other sections of the project include:
• Construct a new interchange at 24th Avenue to connect to SR 509
• Building a new South 216th Street I-5 overpass. This new overpass provides pedestrian and bike access, which does not exist on the current 216th Street bridge.
• SR 509/24th Avenue South to South 188th Street where SR 509 currently ends
• Add a southbound auxiliary lane on I-5 between SR 516 and South 272nd Street between 2024 and 2028.
About $1.6 billion of the $2 billion Gateway Program will be covered from the Connecting Washington funding package approved by the Legislature in 2015 to pay for $16 billion worth of projects across the state, primarily from an 11.9-cent gas tax hike that started in 2016. Another $130 million is from local contributions, including about $60 million from the Ports of Seattle and Tacoma. The city of Kent kicked in $2 million.
Users of the new SR 509 Expressway will have to pay a toll, which is expected to raise another $180 million. Federal and state grants will cover the rest of the costs. The split between the SR 167 and SR 509 projects is about $1 billion each.