The cab of a tractor-trailer rig burned on the side of the road at the 110 mile marker of Interstate 30 west near Benton at approximately 4 p.m.Thursday. According to fire officials, the driver was not injured in the incident. The cause of the fire is under investigation, but preliminary findings suggest a mechanical malfunction. Traffic was backed up into the Benton city limits near South Street for approximately one hour while crews extinguished the fire and removed the rig from the highway. Units from the Benton Fire Department responded.