A contracted road worker hired by CalTrans was killed and another seriously injured when they were struck on the shoulder of State Route 71 in Chino—about 35 miles east of Los Angeles—May 6 by a person driving a truck, according to authorities.

The California Highway Patrol told local news agencies Monday a Peterbilt box truck sideswiped the workers’ parked van and ran through a guardrail before striking them, CHP Officer Rodrigo Jimenez told the Associated Press.

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 injuries.

The 34-year-old truck driver, a resident of Pomona, was treated at a local hospital for minor injuries. Police say the driver was tested for alcohol and drug use and was found not to be impaired. He was not arrested.

An investigation is currently underway to determine why the truck driver lost control on the highway.