Two northbound lanes of Interstate 5 in Centralia have reopened, but one remained closed at 4 p.m. as crews continue to clean up 1,800 gallons of used oil that spilled over three miles when a tanker truck rolled over on Wednesday morning.

The driver of the tanker truck was arrested on suspicion of driving under the influence, according to the Washington State Patrol.

The rollover was reported on Twitter around 6 a.m. by DOT officials, who warned that it was causing a six-mile backup at one point. The DOT said crews are working to clean up the oil as quickly as possible and open at least one lane, but officials urged drivers to delay travel or use alternate routes.

It’s likely, they said, that one lane remain closed through Thursday morning.

“The spill has left oil across all northbound lanes and has soaked into the surface,” WSDOT Tacoma Traffic said earlier Wednesay. “It means there are several miles of slippery roadway. We’re working to reopen at least one lane of northbound I-5 as soon as possible.”