Friday, November 12, 2021

First major stage of SR 509 Completion project starting soon

By Lizzy Buechel

As usual this fall, we are seeing shorter days and leaves changing colors. If you drive in south King County or live or work near I-5 in Des Moines, Kent, or SeaTac you may also notice another change: the beginning of construction on the SR 509/I-5 to 24th Avenue South Expressway project. This four-year project starts sometime in November, depending on weather.

Through the SR 509/I-5 to 24th Avenue South Expressway project, we will provide a new connection to Sea-Tac International Airport, reduce truck travel on local roads, and improve access and safety for those who walk, roll, and use transit in the area. This work is part of the SR 509 Completion Project, which will extend SR 509 from where it currently ends at South 188th Street, to I-5.

This blog is the first in a series that will inform you about construction and what you can expect each step of the way. We start with a detailed look at where we are beginning construction – the I-5/SR 516 Interchange and the South 216th Street Bridge.

Want more information? Check out the SR 509/1-5 to 24th Avenue S. – Expressway Project Online Open House to find more details around SR 509 construction including primary work zones and schedules. The online open house is open through December 13.

I-5/SR 516 Interchange
The biggest change to the I-5/SR 516 interchange will be the construction of a new Veterans Drive undercrossing of I-5. The new undercrossing and Veterans Drive extension will provide a relief valve for drivers going to and from the Kent Valley, as it includes new access to both directions of I-5 and the new SR 509 Expressway. Combined with new and reconstructed ramps at the existing interchange, drivers will have a smoother trip through the area and new options for getting to where they want to go.

The first thing drivers may notice this fall is a slight shift of southbound I-5, which will move towards the median so that crews can widen the I-5 bridge over Kent-Des Moines Road. Crews will also be shifting lanes on Kent-Des Moines Road under I-5.

If you walk, roll, or use transit in this area you can expect the access you have today until 2024, when one of the two eastbound bus bays will temporarily close. The new eastbound SR 516 bus stop will open later in 2024.

If you live or work in the area you can expect typical construction impacts including heavy equipment, noise, and nighttime work on I-5.

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.

South 216th Street Bridge
To build the new ramps to the SR 509 Expressway, we need to demolish and replace the existing South 216th bridge. Unlike the existing bridge, the new bridge will include sidewalks, bike lanes and a turn lane, to make it easier and safer for all people to get across I-5 in this location. Those who walk and roll will have access across the bridge throughout construction.

The new bridge will have one lane in each direction, a center turn lane, 5-foot-wide bike lanes and 6-foot-wide sidewalks.

Crews will construct the eastbound lanes of the new bridge next to the existing bridge, between early 2022 and early 2023. During this stage, the bridge will be open to both directions of traffic, but there will be changes on I-5 where we will reduce lane widths and shift lanes on I-5 between SR 516 and South 200th Street. This will allow crews to build the new bridge and ramps connecting I-5 to the new SR 509.

From mid-2023 to late 2023, we will demolish the existing South 216th Street bridge, and construction on the westbound lanes of the new bridge will begin. During this second stage, the bridge will close to eastbound traffic for approximately six months. A signed detour route will direct drivers across I-5 at South 200th Street.

The new South 216th Street bridge will be open during stage three of construction, with periodic lane closures. The new bridge will fully open by the end of 2023/early 2024.

The new bridge will be built in stages to minimize affects to the traveling public.

Drivers can expect nighttime lane closures on I-5 in 2022 and 2023 when crews demolish the old bridge and set girders for the new bridge. When these lane closures happen, all but one lane of either northbound or southbound I-5 will close overnight, typically between 10 p.m. and 4 a.m. Drivers can also expect periodic single and double lane closures at night throughout construction.

Need a quick refresher?
The SR 509 Completion Project is part of the Puget Sound Gateway Program, which also includes the SR 167 Completion Project. Together these projects will help truck traffic move more efficiently and ease congestion throughout the Puget Sound region. These improvements will enhance the state's economic competitiveness, both nationally and globally, connecting the state's largest ports to key distribution centers in King and Pierce counties.

When finished, SR 509 will provide new access to the airport, allow drivers to bypass I-5, SR 518, and help get freight off local streets. That means, among other things, less truck idling and related CO2 emissions in the area due to heavy traffic. In addition to SR 99 tunnel improvements, this project will also create a critical north-south alternative to I-5 through Seattle and King County.

The project will improve access through the area with interchange improvements, new ramps that connect I-5 to SR 509, and the first mile of the SR 509 expressway.

The SR 509/I-5 to 24th Avenue South Expressway Project is the first major stage of the greater SR 509 Completion Project. This first major stage of construction will begin in late 2021 and will end in 2025. We will complete the SR 509 Completion Project with Stage 2 between 2024 and 2028.

If you still have questions, you can call the construction information line at (206) 225-0674 or email the project email at