State police said Thursday the cause of bus driver George Wetherby's death remains unknown.
Wetherby, 68, of Olean, was driving a Blue Bird Bus Line Inc. motor coach at 7:40 p.m. Tuesday when in went off the Southern Tier Expressway near Almond.
Coroner Dr. David P. Schwert of Alfred pronounced Wetherby dead at the scene and ordered an autopsy at the Monroe County medical examiner's office in Rochester.
Troopers said Wetherby was alone in the bus, westbound on Route 17 four miles west of the Almond exit, when it left the roadway and crashed into woods along the highway.
The bus was taken to the state police forensics laboratory in Olean for a mechanical examination.