A tractor-trailer driver was killed early this morning on I-84 in Greenville after state police say he apparently fell asleep while driving in heavy-fog conditions.

The driver, 60-year-old Robert Mull, was heading eastbound near exit 2 at around 5:30 a.m. when he struck the center median, causing his vehicle to roll over.

Investigators pronounced him dead at the scene.

Shortly after the first accident, a second tractor-trailer collided with another truck, also on I-84 eastbound, and rolled over. Investigators say the second accident was likely caused by the foggy conditions. No one was injured.