A witness told police the woman was riding in the back of a food delivery van when she somehow fell or jumped off the back at about 7:30 a.m. as the vehicle was going westbound on the bridge.

Medics rushed her to Harborview Medical Center in Seattle, where she died shortly after 10 a.m.

The incident caused authorities to close two westbound lanes of the West Seattle Bridge and block ramps from Interstate 5 to the bridge. Morning commute traffic was backed up for miles.

Police said it wasn't clear whether the woman jumped or fell from the van. They said a witness reported the van was bright red, with the letters "BBQ" or the word "barbeque" on the back.

Officers found the van not far from the scene after the driver called 911, police said. Police spoke with the driver, who was cooperative.