( CNN ) -- The driver of a charter bus that overturned on a Minnesota freeway , killing two women , may have had a medical emergency , a spokesman for the State Patrol said Thursday . `` One factor being considered is whether the driver suffered a medical episode while behind the wheel , '' Patrol Capt . Matt Langer said . The driver , 52-year-old Edwin Erickson of Elgin , was hospitalized in serious condition , authorities said . Langer said he had a valid driver 's license . The women who died , both from Minnesota , were identified Thursday as Rhonda Hill , 52 , of Plainview and Pamela Holmquist , 56 , of Kasson . The accident happened Wednesday after the bus left a casino in Rochester , Minnesota , headed for Northwood , Iowa , Langer said . Watch video of tour bus crash site . Erickson and 21 passengers were injured when the bus went out of control outside Austin , Minnesota , authorities said . They said two people were in critical condition , and one person was unhurt . Andy Skoogman , spokesman for the Minnesota Department of Public Safety , said the bus was eastbound on Interstate 90 when it veered across a median and westbound lanes before overturning and landing in a ditch on the side of the road . The wreck happened three miles west of Austin . No other vehicles were involved . Authorities said weather conditions did n't appear to be a factor in the accident .
Charter bus overturned on Minnesota freeway , killing two women . Driver hospitalized in serious condition ; officials looking into possibility of `` medical episode '' 22 people were aboard bus en route to Iowa casino ; only one unhurt .