BOWLING GREEN, Va. — Several survivors of a deadly bus crash in Virginia last year told a judge Thursday of their harrowing early-morning ride, describing how they swerved from side to side and changed speeds erratically before careening off an interstate highway.

After the testimony, a judge convicted Kin Yiu Cheung of four counts of involuntary manslaughter in the crash along Interstate 95 that killed four and injured dozens. The witnesses said the erratic driving occurred for up to an hour as Cheung drank coffee and Red Bull energy drinks. Finally, they said, he nodded off at the wheel and lost control of the low-fare Sky Express bus.