Triangle project: Construction on Federal Way I-5 interchange starts this summer

Work to the SR-161/SR-18/Interstate 5 interchange, known as the triangle project, will be awarded to a bidder in June. Work will begin in August. The construction will replace two cloverleaf ramps with flyover ramps. - Courtesy image
Work to the SR-161/SR-18/Interstate 5 interchange, known as the triangle project, will be awarded to a bidder in June. Work will begin in August. The construction will replace two cloverleaf ramps with flyover ramps.
— image credit: Courtesy image

Construction on the much-anticipated triangle project will begin this summer.

The Washington State Department of Transportation will award phase one of the Interstate 5/State Route 161/State Route 18 interchange — known as the triangle project — to a bidder in early to mid-June, spokesman Mike Murphy said. Construction will begin in August. When completed, the project is expected to increase safety and traffic flow by decreasing weaving traffic at the interchange. Two cloverleaf loop ramps will be replaced with flyover ramps to achieve the goal.

"The idea behind the phasing was to fix the worst of the worst first," Murphy said.

The construction will occur in two phases. The first phase includes building a two-lane flyover ramp connecting westbound SR-18 to southbound I-5. The westbound SR-18 to northbound I-5 ramp will be rebuilt to accommodate the new flyover ramp. An exit ramp connecting the new flyover ramp to SR-161 at South 359th Street will also be constructed. Additionally, a new eastbound SR-18 to northbound I-5 flyover ramp will be constructed, and the eastbound SR-18 to southbound I-5 ramp will be rebuilt to accommodate that ramp.

Traffic impact

Phase one is expected to take two years and cause traffic delays at times. For the most part, motorists will have access to the interchange while construction takes place, Murphy said. Much of the work will be done at night to avoid daytime rush-hour traffic. Noise and environmental variances are likely to be sought, Murphy said.

Anticipated delays and closures will happen periodically over the two-year construction period.

"There will definitely be traffic impacts, no doubt about it," he said. "It's kind of a short-term pain for a long-term gain."

The following major delays are scheduled:

• A 17-day closure of westbound SR-18 to northbound Interstate 5 ramp for realignment. Motorists will be detoured to northbound I-5 via northbound SR-161, northbound Pacific Highway South and eastbound South 320th Street.

• A three-month closure of the Weyerhaeuser Way on-ramp to westbound SR-18 while crews realign the ramp to accommodate the new westbound SR-18 to southbound I-5 flyover ramp. Traffic will be detoured to SR-18 via westbound South 336th Street and southbound SR-161.

• A 10-day closure of the southbound I-5 HOV lane.

• Weeknight lane and ramp closures on SR-18 and I-5.

• Six weekend night full closures of I-5 in one direction.

• Four weekend night full closures of SR-18 in one direction.

• One weekend full closure of the eastbound SR-18 ramp to southbound I-5.

• Three weekend closures of both Interstate 5 HOV lanes. This will reduce the number of freeway lanes through Federal Way from 10 to eight.

• Two weekend closures of the northbound I-5 right lane. This will reduce the number of northbound freeway lanes through Federal Way from five to four.

"During construction, the biggest impact we're concerned about are the days they will be closing westbound (State Route) 18 to northbound I-5," said Rick Perez, City of Federal Way senior traffic engineer.

WSDOT will give advance notice of these closures, and work with local agencies to keep traffic moving as much as possible, Murphy said.

Detours will be established and many locals will make their own detours, Perez. The city plans to adjust traffic signal timing during significant construction periods in an attempt to keep traffic flowing in a timely manner, he said.

Highly anticipated

Federal Way and the state have worked for more than seven years on the project. The first public meeting took place June 2004. A project design was introduced to the public in March 2005. Lobbying for state and federal funds to build the endeavor has been ongoing.

"Obviously, we're very excited to see it finally getting going," Perez said.

To date, $112.5 million is set aside for the triangle work: $100 million is from the 2005 gas tax; $3 million is from the 2003 gas tax; $687,000 is in existing funds; and $8.8 million is federally allocated. Phase one will cost $112 million.

Funding for phase two has not been identified. Regardless of how long it takes to secure the money to complete the final phase, motorists will still see significant traffic and safety alleviation from the first phase, Murphy said. But completing both phases will help reduce long-term congestion and safety concerns at the South 348th Street/SR-161 intersection, Perez said.

"We're going to continue to be aggressive to try to get the rest of the project funded," he said. "Once it's done, it will be a much more efficient and safe interchange."

Check it out

To keep updated on the project, visit the WSDOT website at Individuals may also subscribe to receive WSDOT e-mail updates on South King County projects.

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