A man is in critical condition after being hit by a pick-up and an 18-wheeler.

Investigators say that man walked on I-35 South near the upper and lower level split around 3 a.m. Sunday.

Police say they received three calls on the incident.

The first call was for a man walking on the highway. The second call was for a man lying in the main lanes of the highway. The third call came from the driver of the 18-wheeler.

According to police, the man was initially hit by a pick-up driver who failed to stop,  and then was hit by the 18-wheeler.

Investigators found a license plate from the pick-up underneath the victim.

The man was taken to SAMMC in critical condition.

Police continue to investigate.