Park Record Media Center

This frame grab provided by KXAS-TV shows emergency personnel at the scene where a chartered bus overturned on a highway near Dallas-Fort Worth International Airport in Irving, Texas. Authorities say at least six people are hospitalized. (AP Photo/Courtesy KXAS-TV) ( Bus Crash Texas )

Rescue workers surround an overturned bus on the President George Bush Turnpike in Irving, Texas April 11, 2013, in this still image taken from video courtesy NBCDFW.com. Forty people were on board the bus when it overturned. At least 16 are believed injured according to media reports. REUTERS/NBCDFW.com/Handout ( USA/ )

Emergency responders works the scene of bush crash on the George Bush Turnpike Thursday, April 11, 2013, in Irving, Texas. The chartered bus overturned on the busy highway near Dallas killing at least two people and injuring several others, authorities said. (AP Photo/LM Otero) ( Bus Crash Texas )

First responders are on the scene of a Cardinal Coach Line charter bus accident on Hwy. 161 in Irving, Texas on Thursday morning, April 11, 2013. (AP Photo/The Dallas Morning News, Tom Fox) ( Bus Crash-Texas )

This frame grab provided by KXAS-TV shows emergency personnel at the scene where a chartered bus overturned on a highway near Dallas-Fort Worth International Airport in Irving, Texas. Authorities say at least six people are hospitalized. (AP Photo/Courtesy KXAS-TV) ( Bus Crash Texas )