HYAK, Wash. — With serious spring construction planned for Interstate 90 just east of Snoqualmie Pass, officials are warning drivers they could face major delays starting next week.

Starting Monday, traffic will be restricted to one lane in each direction, according to the state Department of Transportation.

The restrictions are scheduled to last for three weeks. But to accommodate heavy weekend traffic, road crews will adjust and reopen an eastbound lane Fridays and a westbound lane Sundays, said Meagan McFadden, a spokeswoman for the DOT in Yakima.

Crews will be working to build the detours for the summer construction season so traffic can shift while work continues on the new lanes, McFadden said. They also plan to raze the snow shed.

McFadden predicts the most severe delays will be from April 12-26. She suggests that drivers who need to get to Seattle for an appointment or to catch a flight plan ahead and travel during the early morning or late evening hours, when traffic is light.

“If drivers decide to go and don’t heed our warnings now, they could see delays between two to five hours if they don’t change their plans,” McFadden said. “We’re trying to be proactive. We know it’s an inconvenience; that’s why we want to try to get people to schedule around the work and the traffic delays.”

She also suggested checking the DOT’s updates and traffic volume charts on its website, www.wsdot.wa.gov/projects/i90/whatshappening and considering taking alternate routes such as U.S. Highway 12 over White Pass or U.S. Highway 2 over Stevens Pass.

By late April, the detour routes should be set up and ready for two lanes of traffic to resume, McFadden said. Even once the detours open, it’s going to be a busy construction season this summer, with regular hourlong rock-blasting delays in the early evenings on weekdays and other minor delays, she added.

The construction is part of a $551 million project to widen and improve the I-90 corridor from Hyak to the Keechelus Dam. The DOT predicts the project will be finished in 2018.

“The reason we are doing single-lane closures now is because we want to try and get all this major stuff done before the summer,” McFadden said. “It’s critical to get detours in place to start building those new east- and westbound lanes.”