A Boise woman was killed early Monday when she was hit by a tractor-trailer as she sat on the centerline of Idaho 52 in western Gem County, the Idaho State Police said.

They identified the victim as Wendy Young, 31.

Investigators said they had yet to determine why Young was sitting by herself in the middle of the highway shortly before 3 a.m.

They said there was no sign of a car in the vicinity, and no suicide note was found.

The trucker told police that he did not see Young until she appeared in his headlights and by that time it was too late to avoid hitting her.