The National Transportation Safety Board (NTSB) sent a team of investigators to Sherman, Texas to investigate a charter bus crash that occurred Friday morning.

The bus, which was carrying 55 passengers from Houston to Missouri who were on a pilgrimage, ran off a Highway I-75 overpass and landed on its side. It is believed that the bus may have blown a tire. At least 13 were fatally injured, while at least 40 were sent to area hospitals, according to Associated Press reports.

NTSB Highway Investigator Robert Accetta will serve as investigator-in-charge and lead the six-member team, including a member from the Office of Transportation Disaster Assistance, according to an NTSB statement.