A contract worker was killed and another was seriously injured when a box truck veered onto the shoulder of a Southern California freeway, authorities said.

The crash happened Monday morning as a cleanup crew of about seven employees hired by Caltrans was working behind a guardrail along State Route 71 in Chino Hills, according to the California Highway Patrol.

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The Peterbilt box truck sideswiped the workers' parked van and barreled through the guardrail, striking two people, said CHP Officer Rodrigo Jimenez.

A 54-year-old man was pronounced dead at the scene by the Chino Valley Fire Department. The second worker, a 36-year-old man, was hospitalized with major injuries, the Los Angeles Times reported.

The 34-year-old driver of the box truck was treated at a hospital for minor injuries. The driver, a resident of Pomona, complied with a sobriety test and was not impaired, Jimenez said.

The man was not arrested. Investigators were still trying to determine why he lost control on the highway about 30 miles east of downtown Los Angeles.

Two northbound lanes were closed into Monday afternoon.