An appeals court has upheld a bus driver's convictions for a Virginia crash that killed four passengers, injured dozens and cast national attention on low-fare carriers operating on the East Coast.

Kin Yiu Cheung dozed off as he was driving a Sky Express bus from Greensboro, N.C., to New York City just before dawn on May 30, 2011. The bus with 57 passengers aboard veered off Interstate 95 about 30 miles north of Richmond and overturned. The National Transportation Safety Board concluded that driver fatigue likely contributed to the crash because Cheung had limited opportunities for quality sleep the previous few days.

Cheung was convicted of four counts of involuntary manslaughter and was sentenced to six years in prison.

The Virginia Court of Appeals on Tuesday rejected Cheung's claim that prosecutors failed to prove he demonstrated reckless disregard for human life. The court said there was ample evidence Cheung knew he was in no condition to drive, including his heavy consumption of energy drinks and his own admission to police that he was sleepy right before the crash and that he fell asleep while driving.

Cheung's attorney, Taylor B. Stone, did not immediately return a telephone message Wednesday.

Witnesses at Cheung's 2012 trial described a harrowing experience as the bus swerved from side to side and changed speeds erratically for up to an hour while the driver guzzled coffee and energy drinks that he had picked up at stop along the route. A passenger who speaks Mandarin overheard a cellphone conversation in which Cheung told someone in his native language that he doesn't get enough rest.

Passengers testified that when the bus hit rumble strips on the shoulder of the highway, they noticed the driver slumped to the right with his head on his shoulder.

"Given the difficulty that he had driving the bus during the hour before the crash, Cheung should have realized that his impaired condition was affecting his driving and posing a risk to the safety of those on the bus," the appeals court said.

The accident caught the attention of government safety officials, who in June 2012 shut own more than two dozen similar curbside bus operations for safety violations. The NTSB said Transportation Department officials had been in the process of shutting down Sky Express at the time of the crash but had given the company an extra 10 days to appeal an unsatisfactory safety rating.