The northbound lane will be for carpools and is expected to open by the end of 2022.

EVERETT — Relief is in sight for the 65,000 drivers who use I-5 between Everett and Marysville each day.

Originally a peak-use shoulder lane was proposed for the congested corridor. Instead, the state Department of Transportation will add a full-time fourth northbound lane between the exit to Marine View Drive and Highway 529, the agency announced over the weekend.

The new lane will be reserved for carpools, extending the existing high occupancy vehicle lane to Marysville.

Near the Marine View Drive exit, where I-5 currently sheds a lane, WSDOT will reduce the width of the three general-purpose lanes from 12 to 11 feet and narrow both shoulders to make room. The shoulder on the left side will be reduced to about 2 feet, with the right side shoulder decreasing to about 10 feet.

Two new onramps — one from northbound I-5 to 529; the other from 529 to southbound I-5 — are also part of the plan.

The $84.4 million project is set to start construction in spring 2021. It is funded by the Legislature’s Connecting Washington Package, which passed in 2015.

After a little more than a year of construction, WSDOT expects the new lane and onramps to open in late 2022.

The agency considered several options to relieve congestion and improve traffic flow between the two cities. With traffic data showing that nearly a quarter of all vehicles were carpools, WSDOT went with adding an HOV lane.

“The HOV lane addresses the demands not only on weekdays but also weekends,” said Kris Olsen, a spokeswoman for WSDOT. “Our modeling shows we will likely see the HOV lane during peak times moving at 43 miles per hour.”

WSDOT data also shows the project could reduce delays all the way to Highway 530 near Arlington.

With more options to exit I-5 into Marysville, that also should help improve traffic in north Snohomish County, Olsen said.

Most of the restriping and other work needed to add a fourth lane will be done overnight, she said.

Lizz Giordano: 425-374-4165; egiordano@heraldnet.com; Twitter: @lizzgior.