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 Â½ 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 .
`` Black ice was involved '' in Oregon crash that killed 9 , hurt 39 , attorney says . Driver had 7 1/2 hours of sleep the night before , attorney says . Canadian bus company had record of violations in U.S. before fatal wreck .