According to reports, the tour bus was not on the pre-approved route when it was struck by a freight train in Biloxi, Mississippi.
National Transportation Safety Board member Robert Sumwalt revealed that the bus driver may have been following a GPS set for commercial vehicle use rather than the directions provided by the tour company overseeing the excursion.
Two other buses successfully followed the route provided by Florida-based Diamond Tours.
Sumwalt has previously commented on reports that tractor-trailers bottoming out at the railroad crossing. Two other collisions were recorded at the same crossing in January of this year and in August 2014.
Federal investigators are trying to determine in the steep grade also played a role in this latest incident.
Four people were killed in at least 40 others were injured in the accident. The bus was transporting Texas tourists to a collection of Gulf Coast casinos.
The bus was bound for a casino in Biloxi when it was struck by a freight train around 2:15 pm on March 7. The impact from the crash pushed the bus about 300 feet along the tracks.
The casino tour was organized by a senior citizens’ center in Bastrop, Texas.
The following information is provided by the Federal Motor Carrier Safety Administration (FMCSA):