We lay out plans for the new tolling system, set to launch in 2024, after a longtime Interstate 405 commuter contacted us with concerns over the project’s scope.

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In 2019, work crews on Interstate 405 will start building a new lane in each direction between Renton and Bellevue, as part of a series of changes that aim to improve traffic flow on what officials call Washington’s worst corridor for congestion.

Then, five years later, the Washington Department of Transportation (WSDOT) will open the new lanes, and an existing one each way, to traffic as express toll lanes, extending the interstate’s current tolling system between Lynnwood and Bellevue that opened in 2015.

This week’s column reviews plans for the project between Highway 167 in Renton and downtown Bellevue, which includes adding auxiliary lanes in some areas and interchange work, after a longtime I-405 commuter contacted us with concerns over the freeway’s traffic and WSDOT’s plans.

Traffic Lab is a Seattle Times project that digs into the region’s thorny transportation issues, spotlights promising approaches to easing gridlock, and helps readers find the best ways to get around. It is funded with the help of community sponsors Alaska Airlines, CenturyLink, Kemper Development Co., NHL Seattle, PEMCO Mutual Insurance Company, Sabey Corp., Seattle Children’s hospital and Ste. Michelle Wine Estates. Seattle Times editors and reporters operate independently of our funders and maintain editorial control over Traffic Lab content.

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“My wife and I are looking to move because of the transportation issue,” said Dave Burger, who lives near Kent’s East Hill neighborhood.

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He said he switched from driving to taking the bus to work in the Seattle or Bellevue area this spring, now spending about 1½ to 2 hours on trips each way.

WSDOT says the upcoming I-405 project will cut driving time in the general-purpose lanes by about 30 percent, a malleable prediction considering the region’s booming population and evolving transportation trends.

“What we think is happening today might be different, and certainly that is one of the things that happened on the north end,” said WSDOT’s I-405 project director Kim Henry, referring to the region’s unexpectedly fast recovery from the economic recession. “We came right back where we were and then some.”

A rush-hour trip between Tukwila and Bellevue, the stretch WSDOT uses for making traffic projections, in the current HOV lanes takes around 24 minutes, with the worst commutes reaching 34 minutes, according to the agency.

WSDOT will spend $1.22 billion on the upcoming project, funded by the statewide gas-tax increase approved by the Legislature in 2015. That tax increase supports $16 billion in transportation projects across Washington.

Bus-rapid transit, as promised by Sound Transit 3, will use the new express lanes, meaning buses will run with fewer stops and at a quicker pace.

“We’re trying to get all of our infrastructure done in time to get that bus rapid service when it comes online,” Henry said.

Two toll lanes run alongside at least three general-purpose lanes each way between Bellevue and Bothell, while one toll lane and two general lanes run each way between Bothell and Lynnwood. The toll lanes often create a chokepoint where they go from two to one at the Highway 522 interchange.

“Between us and the Legislature, we all said, ‘Let’s not do that again,’ ” Henry said, referencing the plans to have two toll lanes each way for the entire Renton-Bellevue stretch.

Improved signage and access points to reduce unsafe weaving are also lessons learned from the north end project, he said.

Critics have long fought I-405 express toll lanes, saying they don’t make their trips better, while state transportation officials say the toll lanes are saving drivers between Lynnwood and Bellevue 11 to 14 minutes on average.

The express toll lanes are free for carpools carrying at least three people at peak commute times. Nights, weekends and six holidays — including Christmas Day and New Year’s Day — are free to all.

According to a new report by University of Minnesota experts, requested by state lawmakers, speeds in the general lanes improved at first but settled back to previous levels this year.

The report also proposes raising toll rates beyond the current $10 maximum during busy times to keep traffic moving.

Hours after the report’s release on Dec. 13, Henry said the south-end tolling project would need to operate like the north end. “As of today, we’re not proposing any changes to the north end,” he said.

WSDOT spokeswoman Emily Pace followed up last week in an email: “Increasing the maximum toll rate would need to be a discussion between the state Legislature and the Washington State Transportation Commission, which is responsible for setting toll rates.”

Beyond the upcoming Renton to Bellevue project, the state budget contains $5 million for preliminary engineering of additional toll lanes north of Bothell.

The state’s long-range I-405 plan includes adding another lane each way along the entire corridor, in addition to the projects underway.

Got an idea, question or suggestion for Traffic Lab?

Last week, we spotlighted trends in the Seattle Department of Transportation (SDOT) 2017 Traffic Report, ranging from crash statistics to bicycle and pedestrian counts. The week before, we compiled a list of traffic laws, ranging from rules on parking to pedestrian do’s and don’ts at intersections.