The driver of a bus that crashed on Interstate 95 in Virginia, killing four passengers and injuring dozens, was sentenced Wednesday to spend six years in prison.

Kin Yiu Cheung was given 40 years with 34 years suspended for his conviction last November on four counts of involuntary manslaughter, Commonwealth's Attorney Tony Spencer said.

"Each day of my life is haunted by this memory ... and I want to apologize to all the passengers," Cheung said before sentencing in a circuit court in Bowling Green.

The bus was en route from Greensboro, N.C., to New York early on May 31, 2011, when it swerved off the road, hit an embankment and overturned about 30 miles north of Richmond.

The crash cast national attention on a growing industry of inexpensive buses that travel the East Coast offering cheap fares, convenient routes and, in some cases, free wireless Internet. Last June, government safety officials shut down more than two dozen similar curbside bus operations for safety violations in the largest single federal crackdown on the industry.

Survivors at trial spoke of a harrowing early-morning ride, testifying that the low-fare Sky Express bus swerved from side to side and changed speeds erratically before careening off the interstate. The witnesses said the erratic driving lasted up to an hour as Cheung drank coffee and energy drinks before nodding off and losing control.

A state trooper testified that Cheung nodded when asked whether he'd fallen asleep behind the wheel. The National Transportation Safety Board said in July that driver fatigue and other factors likely caused the crash, finding Cheung had limited opportunities for quality sleep in the days before the accident.

Cheung's attorneys have called it a "horrendous accident," but contended it was not a case of criminal negligence.

In sentencing the defendant, Caroline County Circuit Court Judge Joseph Ellis said, "This wasn't an issue of chance," the Free Lance-Star (http://bit.ly/149w0CU) reported.

In a report last July on the Sky Express crash, the National Transportation Safety Board found that ineffective government oversight allowed the Charlotte, N.C.-based company to operate despite various safety violations.

The board said Transportation Department officials were 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. Without the extension, Sky Express would have ceased operations the weekend before the crash.

Those killed in the Sky Express crash were identified by Virginia State Police as Karen Blyden-Decastro, 46, of Cambria Heights, N.Y.; Sie Giok Giang, 63, of Philadelphia; Josefa Torres, 78, of Jamaica, N.Y.; and Denny Estefany Martinez, 25, of Jersey City, N.J.