TULALIP — For a section of I-5 that sees 100,000 vehicles per day, the two-lane bridge at 116th Street NE joining Marysville and Tulalip just doesn’t cut it any more.

In January, construction crews are set to start work on the bridge deck for a new overpass.

By fall of 2016, a new six-lane bridge should be open to traffic, at which point the crews will begin the final phase of reorienting the on- and offramps.

Traffic over the existing two-lane bridge already is bad, with cars on the northbound off-ramp frequently backing up onto I-5.

The project is expected to drastically reduce gridlock in a part of the county that’s seen a lot of growth in the past 15 years.

“It wasn’t just for the business park, it was for the region,” said Debra Bray, the project manager for the Tulalip Tribes that has led the project.

The business park Bray referred to is the Quil Ceda Village shopping center and business park, which didn’t exist when the current interchange was built in 1971 and the surrounding area was largely rural.

The Consolidated Borough of Quil Ceda Village incorporated in 2001, and what are now 150 businesses moved in, including the Seattle Premium Outlets mall, Walmart, Home Depot, and Cabela’s. The Tulalip Casino and Resort also made the area a hub for nightlife.

Nowadays 25,000 vehicles a day exit I-5 at 116th Street, affecting both businesses and nearby neighborhoods.

“The huge volume of residents living in the Firetrail area, it wasn’t meeting their needs,” Bray said.

There’s still room to grow. Only a fraction of the 2,000 acres of Quil Ceda Village has been developed.

Across I-5, the city of Marysville also is reviewing an application to build a 100-room Hilton Hotel just south of the interchange, plus an additional 10,000 square feet of restaurants and retail, said Chris Holland, a senior planner with the city.

The Tulalip Tribes sought to build a key piece of infrastructure to accommodate growth in the area.

Unable to secure federal transportation funding for the construction, the tribes had to carry much of the $32.1 million in construction costs so far, Bray said, with $8 million being contributed from the Puget Sound Regional Council last year.

On Dec. 9, the Snohomish County Council has scheduled a public hearing on a plan to contribute another $1 million in matching funds toward final construction, said Doug McCormick, a county public works manager.

The tribes also extended Quil Ceda Boulevard north in 2007, widened 116th Street NE west of the interchange and built new culverts under I-5 and 34th Avenue NE to accommodate fish in Quil Ceda Creek. The city of Marysville has likewise improved 116th east of the interchange.

The new bridge should help reduce some of the gridlock on the bridge simply because the new deck will have more space for cars, McCormick. Backups on the northbound off-ramp often spill onto I-5.

“The real benefit will be when they’re able to move ahead with the ramps,” McCormick said.

New on- and offramps will be the final phase of the project, starting after the new deck is finished and wrapping up in the spring of 2017.

The construction of the new bridge deck and ramps will be staggered so that the bridge will always be open, Bray said.

The ramps will feature space for Community Transit buses to stop, coordinated signaling and metering to help get vehicles on and off the freeway.

The state transportation package for the next six years identifies $50 million in funding for the ramps and the next project on the Tulalip Tribes’ agenda: the 88th Street NE interchange.

The bridge deck of 88th Street NE is in good shape, Bray said, but the ramps need to be improved and sidewalks installed over the freeway.

“It’s all related to pedestrian movement, and safety improvements and ramp improvements,” she said.

Chris Winters: 425-374-4165; cwinters@heraldnet.com. Twitter: @Chris_At_Herald.