The accident on the New Jersey Turnpike June 7 killed comedian James McNair and seriously injured Morgan and two other passengers.
The National Transportation Safety Board's preliminary report, released Thursday, concludes that Kevin Roper was driving his Wal-Mart truck at 65 mph before the crash.
The area's speed limit is 55 mph and traffic was slowed to 45 mph due to construction.
The report says Roper had been on the job about 13 1/2 hours at the time of the crash.
Federal rules limit drivers to 14 hours of work per day with a maximum of 11 hours behind the wheel.
Wal-Mart didn't comment on Roper's schedule.