WASHINGTON • A speeding Wal-Mart truck driver who had been awake for 28 hours was held responsible on Tuesday for a highway crash last year that left 30 Rock star Tracy Morgan (above) with brain injuries and killed a fellow comedian, United States transport regulators said.

The National Transportation Safety Board (NTSB) also concluded in a review that the injuries to Morgan and other passengers were exacerbated by their failure to wear seat belts.

Changes to the interior of their limousine van trapped them inside for about 40 minutes after the vehicle overturned in the June 7 collision last year on the New Jersey turnpike, the board said.

Morgan, 46, suffered serious brain injury and broken bones and was left in a coma. The Saturday Night Live star has not performed since the accident.

Comedian James "Jimmy Mack" McNair, 62, was killed and nine other people were injured in the chain reaction collision that involved 21 people in six vehicles.

In a public hearing, NTSB officials said the Wal-Mart truck driver had driven 1,287km overnight to the company's distribution centre before embarking on his delivery, and had been awake for more than 28 hours at the time of the crash.

The truck was driving at 104kmh in a 72kmh zone. It did not slow down when entering a road construction zone where it rear-ended the slower-travelling limousine van at about 1 am, the NTSB said.

The van's driver was not wearing a seat belt and only one of the six passengers was strapped in. The others were thrown around inside the vehicle at the time on impact.

Investigators recommended that Wal-Mart improve fatigue management programmes for drivers and install better vehicle warning systems for drivers and delivery operators.

The truck driver Kevin Roper faces charges of vehicular homicide and assault by auto and is awaiting trial in New Jersey.

Morgan and some of the injured parties reached a settlement with Wal-Mart in May.

REUTERS