A suspected drunken driver traveling in the wrong direction on Highway 101 and a man who tried to help her were both killed when they were hit by numerous cars in San Mateo, triggering a 15-hour backup on the freeway, authorities said Monday.

Stacy White, 39, of San Mateo and Steven Pereira, 26, of Dunnigan (Yolo County), were killed in the crash, which happened about 3 a.m. Sunday, the San Mateo County coroner's office said.