Southbound I-5 at Mountlake Terrace to close for rail work

MOUNTLAKE TERRACE — Late-night and early morning I-5 drivers heading south through Lynnwood, Edmonds and Mountlake Terrace the weekend of Nov. 20 should plan for major delays and a detour for light-rail construction.

The construction involves installing supports where elevated track for Sound Transit’s new Link rail line will cross the freeway, just north of the site of a Mountlake Terrace station, according to the agency.

That weekend, closures are scheduled:

• 11 p.m. Friday, Nov. 20, until 6 a.m. Saturday, Nov. 21;

• 11 p.m. that Saturday until 6:30 a.m. Sunday, Nov. 22;

• 11 p.m. that Sunday until 4 a.m. Monday, Nov. 23.

Sound Transit plans to have southbound I-5 traffic exit at 220th Street SW. Vehicles will be routed about 4 miles west to Highway 99, then south to Highway 104, and back onto I-5 at the southbound on-ramp from Highway 104.

Northbound I-5 traffic will be unaffected.

Sound Transit and the agency’s contractor coordinated with the Washington State Department of Transportation for the weekend closure, which affects less than 2 miles of the freeway. The nighttime-only detours should minimize congestion.

“We’re doing it on a weekend, late at night,” Sound Transit spokesperson Scott Thompson said. “Typically those are low-traffic times.”

During the day, that area of I-5 is busy. An average of 104,031 used the stretch daily in October, WSDOT spokesperson Lisa Van Cise said.

Taking traffic off the highway is necessary so crews can install temporary steel columns from the Mountlake Terrace Freeway Station park-and-ride, on the east side of I-5, over the freeway to the west side. From there, the rail line will run north along the freeway to a new station at the Lynnwood Transit Center.

“To actually build it, we have to get equipment and folks on the freeway for that work, which is why we have to close,” Thompson said.

Eventually, crews will install the permanent concrete columns and decks that carry the rail tracks, similar to the elevated span that crosses I-5 in south Seattle en route to Sea-Tac Airport.

“We like to use detour routes that mimic the roadway that we’re closing,” WSDOT Northwest Region construction traffic manager Bonnie Nau said. “Obviously there isn’t another freeway in that area.”

Message boards on I-5 and I-405 will alert drivers to the closure so they can use another route. For people driving through or to Seattle, it could be faster to take I-405.

Highway 99 fit the detour criteria because it has controlled intersections and multiple lanes, and it parallels I-5.

“There’s obviously roadways that are closer to I-5, but those tend to be residential streets,” Nau said.

The state tries to avoid using side streets because of the noise of so many vehicles.

Traffic signals along the detour could be altered to improve flow of the rerouted vehicles, Nau said.

Officers will help control traffic along the detour.

People have watched I-5’s margins transform over the past few years, with clearing and grading for the Lynnwood Link light rail extension from Northgate in Seattle, which will carry train cars every six minutes during peak hours. More work is ahead to build the line, with stations scheduled to open in 2024 — two in Shoreline, one in Mountlake Terrace, one in Lynnwood.

By 2026, Sound Transit estimates between 47,000 and 55,000 daily riders, with the travel time between the Lynnwood City Center Station to Westlake Center in downtown Seattle in just 28 minutes.

Another I-5 closure is likely to happen early next year for similar work over the northbound lanes.

Ben Watanabe: bwatanabe@heraldnet.com; 425-339-3037; Twitter @benwatanabe.