A rookie police officer with the U.S. Navy Yard was killed in a one-car accident, apparently falling asleep at the wheel after working double shifts for at least three days.

Travis Harris, 27, died early Sunday morning in Fairfax County when his 2003 Ford Explorer veered off the road near the intersection of Sherwood Hall and Evening lanes in Mount Vernon and struck a tree. He had graduated from the police academy in March and was working as an officer at the Navy Yard.

"He was a great, great officer," said Harris' supervisor, Lt. Bobby Eason. "He was a big guy, but he just laughed everything off."

Harris had started off as a young crossing guard in Fairfax County and -- after a stint as a federal security guard -- was following his lifelong ambition to be a police officer, Eason said. He was known as a garrulous co-worker, with a passion for the Redskins and his PlayStation 3.

He wasn't wearing a seat belt when his Explorer left the road around 7:30 a.m., Fairfax County police said.

Multiple sources familiar with the crash said Harris was on his way to his mother's house to take a nap when the crash occurred. He had just worked three consecutive nights of overtime, including a 12- and a 15-hour shift, sources said.

Navy Yard police officers have complained for months about dangerous levels of understaffing at the facility. Eason declined comment on the matter.