A Caltrans worker in a truck and two passengers in a separate car were injured Tuesday when the two collided on the shoulder of State Route 78 in San Marcos.
The Caltrans worker was in his truck parked on the eastbound shoulder of the highway underneath the Nordahl Road overpass when his truck was hit from behind by a Jeep SUV.
Medics took the Caltrans worker to Palomar Medical Center with a head injury, and his truck took damage to its rear end on the driver's side.
The driver of the Jeep, identified only as a female passenger, was also taken to Palomar Medical Center.
Investigators are not yet sure what caused the Jeep to swerve into the Caltrans truck.
The collision backed up traffic on eastbound SR-78 significantly. Follow live traffic updates here.