Authorities arrested a man on suspicion of murder who they say stabbed his estranged wife to death and pushed her out of his truck in front of shocked motorists on a busy highway.

The Contra Costa County Sheriff's Department says 47-year-old Robert Woods killed 46-year-old Elnora Caldwell on Saturday, just weeks after she had served him with divorce papers and filed for a restraining order.

Caldwell, who worked at a Nordstrom store in San Francisco, was stabbed repeatedly and pushed out of Woods' truck onto Highway 24, where shocked motorists stopped to aid her.

Authorities say one driver wrote down Woods' license plate number, which helped them find and arrest him on Sunday.

Woods is in the county jail being held on $1 million bail.