EVERETT — Rush-hour traffic backups on southbound I-5 through Everett are likely to get worse this week, with a new construction zone springing up in the middle of the freeway lanes.

The state plans to shut down a middle segment of a southbound I-5 lane on Wednesday night to replace a girder that supports the freeway over Pacific Avenue in Everett.

The eight-week project will reduce speed limits in the area from 60 mph to 50 mph. And drivers will have to weave past the construction zone by merging into lanes on the left or right of the work site.

Traffic on southbound I-5 is already crawling through Everett twice a day during commute hours.

On Feb. 14, crews shut down a segment of a Broadway merging lane onto southbound I-5 to rebuild the road’s shoulder. That has slowed down traffic.

Now the girder replacement project is about to start.

“Another one? Oh my gosh,” said Casey Clark, who drives on I-5 between Mill Creek and Marysville daily.

Clark, 28, drives south on the freeway in the afternoon.

“All the problem I have is with merging” at Broadway, he said.

The closure of the Broadway merging lane has forced drivers to go directly into mainline traffic on the freeway. The change has confused some drivers who were used to merging onto I-5 without such an abrupt lane change.

The I-5 construction zone island over Pacific Avenue could back up traffic even more. At night, additional lanes may be closed, state officials said.

About 90,000 vehicles drive over the Pacific Avenue bridge toward Seattle daily, making the area one of the most heavily used segments of I-5 in Snohomish County, said Patty Michaud, spokeswoman for the state Department of Transportation.

The split of traffic may also confuse drivers, said Washington State Patrol trooper Kirk Rudeen.

“What we want people to do is slow down,” Rudeen said. “We want them to pay attention and have patience.”

As drivers go around the construction zone, they can choose to merge into the two lanes on their left or a single lane on their right. Those who want to exit the freeway onto 41st Street must stay on the right lane.

“Our concern is the last-minute jockeying,” Rudeen said.

Splitting traffic in the center of a freeway is very unusual and can be tricky, state transportation officials said, but they don’t have a choice. The 95-foot-long girder below the middle of the freeway was damaged in December 2006 when it was hit by a truck carrying an excavator.

A temporary fix was made, but the girder needs to be replaced and now is the time to do so, said Mike Cotten, project director for the transportation department’s Everett I-5 widening project.

Crews have widened southbound I-5 in the area to add a new carpool lane, Cotten said. The state plans to use the new carpool lane for general traffic during the construction to move traffic smoothly.

The girder replacement could cost the trucker’s insurer about $1 million, state transportation officials said.

Replacing the girder is necessary before crews can finish the I-5 widening project through Everett, the third-most-expensive highway project in the state’s history. Construction for the $263 million project began in September 2005. The money comes from a 2003 nickel-per-gallon gas-tax hike.

Heavy traffic since the project started has made Tim Hemmelman avoid southbound I-5 from Marysville to Pacific Avenue. Hemmelman, who commutes to Seattle with his wife, said he gets onto the freeway from the Pacific Avenue onramp.

But he may take a different onramp once the girder replacement work starts this week, Hemmelman said.

“Maybe it will impact us, maybe it won’t,” he said.

Nonetheless, Hemmelman said he looks forward to when the I-5 widening project is complete.

“I hope when it’s done, it will be better,” he said.

By the end of April, a new southbound carpool lane will open on I-5 from Marine View Drive to Lowell bridge. Earlier in the year, the state finished widening southbound I-5, including opening a new carpool lane from Lowell bridge to Highway 526, known as the Boeing Freeway.

A new northbound carpool lane is set to open in April from the Boeing Freeway to U.S. 2.

With new onramps and offramps added, a wider I-5 is expected to improve traffic flow through choke points in Everett. The project was originally scheduled to begin in 2009, but the state Legislature expedited the schedule in anticipation of heavy traffic during the 2010 Olympic Winter Games in Vancouver, B.C.

Reporter Yoshiaki Nohara: 425-339-3029 or ynohara@heraldnet.com.

I-5 widening project

The state’s I-5 widening project in Everett is expected to wrap up this summer. Here is the timeline for remaining projects.

April 2008: A southbound carpool lane between 41st Street and Lowell Bridge opens.

A southbound carpool lane between Marine View Drive and 41st Street opens.

A southbound merging lane between U.S. 2 and 41st Street opens.

A northbound carpool lane between Highway 526 and U.S. 2 opens.

May 2008: A Broadway offramp from northbound I-5 opens.

A Broadway onramp to southbound I-5 opens.

A 41st Street onramp to southbound I-5 opens.

June 2008: New traffic cameras and ramp meters get installed.

Source: Washington Department of Transportation.