An 18-wheeler leaking motor oil fluid shut down two westbound lanes on Interstate 10 Tuesday, Aug. 8.
The closed interstate lanes are between the West Prince and West Ruthrauff roads exit, said Capt. Brian Keeley of Northwest Fire District.
Keeley said the lanes were expected to re-open by 9 p.m.
Hazardous material crews tested samples of the then unknown substance, said Keeley. Shortly before 8:30 p.m., crews learned it was motor oil. Passersby reported the semi-truck leaking the substance.
He said Arizona Department of Public Safety troopers have taken over the scene.