It happened just after 12:30 p.m. near Hayden Road.
According to Merced California Highway Patrol officers, eastbound traffic had stopped for the big rig making a left turn into a driveway. The woman, traveling from behind, failed to stop and swerved left to avoid a collision with other vehicles and slammed into the turning truck.
The woman was pronounced dead at the scene. Her identity is not known at this time.