Making his first trip of the day, the operator of Green Line car 3892 should have been rested. Instead, he had just finished moonlighting at another job, leaving him so drowsy, investigators have concluded, that he allowed his trolley to ram another last week at Boylston Street Station.

MBTA leaders said Wednesday that the operator was solely responsible for the rear-end crash and fired the 46-year-old operator less than a week after he was supposed to receive an award for safe driving.