San Ysidro

A 20-year-old woman was killed Wednesday after her car was struck from behind on Interstate 5 while visibility was restricted by dense fog, the California Highway Patrol said.

Celia Perez of Southeast San Diego was northbound on I-5 just south of its junction with Interstate 805 at 5:20 a.m. when her car began to have mechanical problems, said Lloyd Needham of the CHP.

Perez pulled onto the left-hand shoulder and was slowing when her car was struck.

The driver of the second car was taken to Scripps Memorial Hospital in Chula Vista and treated for cuts and bruises, a hospital spokeswoman said.

Perez’s sister, Maria, 22, and her 2-year-old daughter, both of whom were passengers, were also treated for bruises at Scripps and released, the spokeswoman said.

The accident is under investigation.

Celia Perez was not wearing a seat belt, Needham said.