Highway1 eastbound is closed while police investigate the accident scene, but is expected to re-open by 1 p.m. PT according to DriveBC.
Regional RCMP duty officer Insp. Davy Lee said the woman ran her car into a ditch at that location and was standing in the dark on the shoulder of the road.
"A crew member of the Department of Highways came upon her and went to assist her. He went down to the vehicle to check it out, She, for some reason, ventured onto the travelling portion of the highway where she was struck by a semi-truck passing by resulting in her fatality."
Lee said police have not determined how the woman drove her car into the ditch. He said it was cold and there could have been black ice on the highway.
He also had no explanation for why the woman left the shoulder of the highway and ventured out onto the road. He said the highway's truck had set its lights and direction arrows to divert traffic and would have been highly visible.
Map: Highway 1 and Prest Road, Chilliwack, B.C