A preliminary report on the crash was issued Friday by the National Transportation Safety Board.
It says the bus was going 78 mph about 45 seconds before the crash. The speed limit at the Bronx crash site is 55 mph.
Police said driver Ophadell Williams told them his bus was clipped by a tractor-trailer, which forced him to swerve and crash. Williams' attorney didn't immediately return a call for comment Friday.
The bus ran off Interstate 95 on March 12 as it was returning from a casino in Uncasville, Conn.. It tipped over and slammed into a pole that sheared it nearly end to end.