BOTHELL — Karen Oliver lives just above the busy intersection where Locust Way meets Larch Way near Bothell.

It’s currently controlled by four stop signs. But to improve traffic flow, Snohomish County plans to put a roundabout at the intersection, which sees more than 10,000 vehicles per day.

Oliver, who along with around 100 others, attended a Snohomish County open house for the project Wednesday. She said she has been caught in that intersection more than once.

“I think the rush hour backup is atrocious. And four-way stops are always really confusing for people,” said Oliver, 47. “It’s like who got here first? ‘You go’ — ‘No, no, you go.’ I think it’ll really help with the backup.”

The project is two-pronged: The roundabout and a bridge replacement along Locust Way, near its intersection with 228th Street SW. They’re being staggered, with the roundabout project coming first. Traffic at the roundabout construction site will deal with single-lane closures in the spring, followed by a full closure while schools are on summer break. Single-lane closures will continue in the fall.

During the full closure, traffic will be diverted to Highway 524 and 228th Street SW. The detour around the construction is over 4 miles — highlighting how critical the intersection is to commuters.

“It’s really the only north-south route through this Bothell-Brier triangle,” said Matthew Feeley, a project manager with Snohomish County.

The detour will be long, but locals knew changing the intersection would come with some short-term cost.

“I think it’s a positive any way you look at it,” said Duane Oestreich, 55, who also lives in the area. “It’s a challenge while they’re building it, but it is what it is. That’s how construction works.”

Traffic and the lack of pedestrian safety are the biggest reasons for the new roundabout. One approach to the intersection is steep and there’s a bit of a blind spot.

Traffic lights were considered for the area, but ultimately the county chose a roundabout.

“If I had a signalized intersection and someone’s coming downhill and they have a green light, it requires them to steer their car mid-intersection to get into the receiving lane, which is highly undesirable because if they don’t steer they end up in traffic,” Feeley said.

The roundabout project will also include paths for bikes and pedestrians.

“I’m excited for it to be safer for people riding bikes and kids walking, because kids walk a lot to get to 7-Eleven,” Oliver said. “So I think improving that walkway will be super beneficial.”

The project did include some permanent and some temporary property acquisition. Ten properties in total were affected, but no full acquisitions were required to complete either project.

Mostly it meant a couple people got new driveways, said Janice Fahning, the county’s director of engineering services.

The bridge project, meanwhile, is slated to start construction in 2025. Swamp Creek Bridge 503 was originally built in 1960 and rebuilt in 1988. At just 22½ feet wide and 41 feet long, it’s tight and narrow. And it’s “structurally deficient and is posted as a weight restricted bridge,” a county report on the bridge stated.

The proposed bridge is nearly double the width, at 47 feet across and 70 feet long.

The bridge “certainly needs to be wider,” said Oestreich. “I have a travel trailer. I’ve come across that bridge and have I’ve had full-size trucks coming at me. It’s not a very pleasant experience. Very stressful.”

The car lanes on the bridge will be 11 feet wide, and the plan also includes a bike lane and a pedestrian path.

The bridge “can’t handle the traffic needs of today,” said Nolan Anderson, the project manager for the bridge replacement. “It’s too narrow … it has no facilities for pedestrians or, bicycles. So there’s no facilities for other users other than vehicles, which is not OK, by our current design standards.”

Bridge 503 crosses Swamp Creek, a salmon-bearing stream. Crews will add woody debris piles and the bridge is being engineered to better facilitate salmon using the creek.

“Basically, we get a more natural stream bank,” Anderson said.

The bridge replacement is expected to cost $3.1 million and the roundabout about $4.5 million.

Jordan Hansen: 425-339-3046; jordan.hansen@heraldnet.com; Twitter: @jordyhansen.