RICHMOND, Va. (CBSNewYork/AP) — Federal officials say a Virginia bus crash that killed four people and injured dozens was likely caused by driver fatigue and several other factors.

The National Transportation Safety Board on Tuesday said the low-fare bus company, Sky Express, had no regard for passenger safety.

“Sky Express’s failure to exercise even minimal oversight of its drivers’ rest and sleep activities enabled the drivers to drive while dangerously fatigued,” the report stated.

EXTRA: Read The Full NTSB Report

The federal agency also said that ineffective government oversight allowed the company to operate despite various safety violations.

The crash happened on May 31, 2011 when a Sky Express bus bound for Chinatown from North Carolina swerved off the road and overturned on Interstate 95 about 30 miles north of Richmond.

Killed were 46-year-old Karen Blyden-Decastro of Cambria Heights, NY, 63-year-old Sie Giok Giang of Philadelphia, 78-year-old Josefa Torres of Jamaica, NY and 25-year-old Denny Estefany Martinez of Jersey City, NJ.

Fifty-four others were injured.

Bus driver Kin Yiu Cheung of Flushing, Queens faces four counts of involuntary manslaughter. Court records show Cheung told police he fell asleep at the wheel. His trial is set for Nov. 8.

Dispatcher Zhao Jian Chen is set to face the same charges in October.

After the crash, federal officials shut down Sky Express for multiple safety violations.

(TM and Copyright 2012 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2012 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)

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