Washington (CNN) -- Black ice -- road ice virtually invisible to drivers -- played a "significant role" in last month's fatal bus crash in Oregon, an attorney for the bus company said Wednesday night.
Attorney Mark Scheer also said bus driver Haeng Kyu Hwang had had 7 ½ hours of sleep the night before the crash, suggesting that fatigue was not a factor, and said there is "no indication" that drugs and alcohol were involved.
On Tuesday, the Federal Motor Carrier Safety Administration barred Mi Joo Tour & Travel Ltd., a Canadian company, from operating in the United States, saying in an order that Hwang had worked 92 hours in the seven days leading up to the crash, far exceeding the 70 hours allowed. It also said that the bus company had not conducted required post-accident alcohol and drug tests on the driver.
An agency spokesman Wednesday night declined to comment on the black ice claim or on the driver's sleep history, citing the ongoing investigation by the National Transportation Safety Board.
The deadly accident occurred December 30 as the large motor coach was returning to Vancouver, British Columbia, from Las Vegas. The bus skidded on Interstate 84 near Pendleton, Oregon, crashed through a guardrail and tumbled down a steep embankment.
Nine passengers were killed and 39 people were injured, including the driver.
"I can say conclusively that black ice was involved from all reports we have of the accident," Scheer told reporters. There were other accidents involving black ice near the crash site, he said.
Scheer said Hwang was properly licensed, had previously worked as a school bus and truck driver and had extensive experience driving in the West. Hwang had slept 7 1/2 hours the night before the crash and had been on the road only 2 1/2 hours that day, including a rest stop, he said. He declined to comment on the claim that Hwang had violated work hour rules that week, saying he was not familiar with the driver's itinerary.
In its 10-page order Tuesday, the motor carrier administration said Mi Joo Tour & Travel poses an "imminent hazard to public safety" because of its failure to ensure that its drivers are properly rested. "Mi Joo does not monitor its drivers' hours of service to ensure that its drivers do not violate" work-hour restrictions, it said. Further, Mi Joo does not require its drivers to maintain driver logs, as required by law, it said.
The NTSB and the Oregon State Police are investigating the accident. FMCSA also is conducting a compliance review of the company, which caters to Korean tourists.
In 2010, the FMCSA cited Mi Joo for 11 violations and gave the company a "conditional" rating, meaning it was in jeopardy of losing its ability to operate in the United States. In 2011, the agency cited Mi Joo for eight violations and gave it a "satisfactory" rating.