WASHINGTON The National Transportation Safety Board has determined that a particularly ugly motorcoach crash near Mexican Hat, Utah, early last year was probably caused because the driver was overly fatigued and as a result wasnt aware he was barreling down a mountain grade with a curve at the end of it.

Nine passengers were fatally injured and 43 passengers, plus the driver, were injured when the coach hit a guardrail, went off the road and rolled completely over, coming to rest on its wheels.

Fifty-one of the 53 people in the bus were ejected when the roof of the coach was sheared off during the roll over.

In an unusual move, the NTSB voted unanimously to place partial blame on the National Highway Traffic Safety Administration, saying the agency's failure to implement motorcoach safety standards -- which the NTSB recommended a decade ago -- was a contributing factor to the crashs severity.

"I am extremely disappointed, watching NHTSA crawl toward the standard we have asked them to make," said acting NTSB Chairman Mark Rosenker.

The board investigates accidents and makes safety recommendations. The traffic safety administration develops and sets regulations.

NHTSA spokesman Rae Tyson declined to comment on the boards action, but said the agency was "working very hard" on new safety standards for motorcoaches. He cited crash tests the agency began conducting in December 2007.

In all, the NTSB made eight safety recommendations to federal and state agencies, trade associations and the motorcoach operator, Busco Inc., doing business as Arrow Stage Lines of Omaha, Neb.

One recommendation is to develop and implement criteria, based on traffic patterns, passenger volume and bus types, that can be used to assess the risks of rural travel by large buses.

Because the crash occurred in a remote, mountainous area of Utah, it took an hour before the first emergency crew arrived. The nearest hospital with a trauma unit was 190 miles away in Flagstaff, Ariz.

The sequence of events laid out by NTSB investigators shows circumstances combined to worsen the accident.

The bus was part of a charter of 17 motorcoaches carrying 800 people. Heavy snow forced the closure of a high mountain pass, requiring the buses to take a longer route back to Phoenix through a remote area of Utah.

The driver of the bus that crashed suffered from sleep apnea and had trouble using a device to regulate his breathing while sleeping in the days before the accident. He also had head congestion and may have been suffering from altitude sickness.

In the darkness and cloudy conditions, and perhaps because of fatigue, the driver took a wrong turn and was on a road that wasn't part of the intended route when the crash occurred.

A passer-by drove eight miles to Mexican Hat, the nearest town, to call 911 on a telephone. Medical helicopters werent able to respond to the accident. Crash victims used their cell phones to provide illumination at the pitch-black crash site but couldnt use the phones to make calls because of the remote location.

In 1999, after another tragic bus crash, the NTSB recommended that safety standards for motorcoach roofs be strengthened, that buses have easy-to-open windows that don't shatter, and that steps be taken, including possibly requiring seatbelts, to prevent passengers from being ejected in rollovers.

Several board members expressed frustration those recommendations have not been implemented 10 years later.

NHTSA has "left motorcoaches back in the '60s and '70s," said Rosenker. "It's time now. It's not like the technology doesn't exist."