SAN DIEGO — A 20-year-old man was struck by a car while walking in traffic on a busy freeway transition in Mission Valley, authorities said Friday.

It was not immediately clear what he was doing on the ramp from Interstate 805 to eastbound Interstate 8 when he was hit by an eastbound 2010 Nissan Sentra driven by a 43-year-old San Diego man around 10:30 p.m. Thursday, according to the California Highway Patrol.

A La Mesa woman in an Infiniti G20 sedan hit the brakes to avoid the Nissan involved in the initial crash, but her car was then struck from behind by a 2006 Dodge Magnum, according to the CHP.

A nurse and a paramedic pulled over to help the injured man.

“My wife saw a body in the road, so we pulled up a little closer. We saw a guy sitting up and he had a bunch of injuries going on, bleeding,” Brian San Miguel, a nurse, described.

The pedestrian suffered moderate injuries and was taken to Scripps Mercy Hospital to be treated. None of the drivers were injured, authorities said.