LITCHFIELD — Authorities say a blown tire appears to have caused the crash of a double-decker bus on a southern Illinois highway in which one passenger was killed and dozens were injured.

State Police Lt. Louis Kink said Friday that the investigation into Thursday's crash near Litchfield could take weeks, but that there doesn't appear to have been driver error.

The packed Megabus veered into a highway overpass support pillar about 55 miles northeast of St. Louis. A University of Missouri graduate student who was sitting above the driver was killed.