A woman was struck and killed Saturday morning by at least one vehicle on the Ronald Packard (78) Parkway in Vista, authorities said. The crash occurred about 5:05 a.m. on the westbound highway at South Emerald Drive, the California Highway Patrol reported. A woman wearing a blue shirt and jeans was seen walking into the lanes of traffic prior to the crash, the CHP said. A SigAlert was issued at 5:34 a.m. closing the Nos. 2 and 3 lanes of the westbound route as well as the Emerald Drive on-ramp. There was no other information immediately available.