On Tuesday, the National Transportation Safety Board (NTSB) determined that the probable cause of a fatal motorcoach accident in Sherman, Texas, was the failure of the right steer axle tire, due to an extended period of low-pressure operation, which resulted in sidewall, belting and body ply separation within the tire, leading to loss of vehicle control.

Contributing to the severity of the accident was the failure of the bridge railing to redirect the vehicle and prevent it from departing the bridge. The lack of an adequate occupant protection system contributed to the severity of the passenger injuries.

The accident occurred on Aug. 8, 2008, when a 2002 56-passenger coach with a driver and 55 passengers on board departed Houston en route to a festival in Carthage, Mo. About four-and-a-half hours into the trip, while traveling northbound in the right lane of U.S. Highway 75, the right steer axle tire failed as the motorcoach approached the Post Oak Creek bridge at a speed of about 68 mph; the bus went through the bridge railing and off the bridge. It fell about eight feet and slid approximately 24 feet on its right side before coming to rest. As a result of the accident, 17 passengers died. In addition, the driver received serious injuries and 38 passengers received minor-to-serious injuries.

Major safety issues identified by this accident investigation include:

• The tire failure and the need for tire pressure monitoring systems on vehicles weighing more than 10,000 pounds.

•  The failure of the bridge railing and the need for criteria for the selection of appropriate bridge railing designs.

• The lack of oversight of the federal commercial vehicle inspections that are delegated to the states.

• The lack of motorcoach occupant protection systems.

• The deficiencies in federal safety oversight of new entrant motor carriers.

As a result of its investigation of this accident, the NTSB made eight new recommendations in these five safety issue areas to three federal agencies: the Federal Highway Administration (FHWA), the Federal Motor Carrier Safety Administration (FMCSA) and the National Highway Traffic Safety Administration (NHTSA).

Two recommendations were made to the American Association of State Highway and Transportation Officials in the area of bridge railing design; one recommendation to the American Association of Motor Vehicle Administrators, regarding tire pressure monitoring procedures; and one recommendation to the motorcoach manufacturer, Motor Coach Industries Inc., calling for revised vehicle maintenance manuals.

The NTSB also reiterated five previous recommendations made to FMCSA and NHTSA in the areas of drug and alcohol testing and motorcoach occupant protection systems.

A synopsis of the NTSB’s report, including the probable cause and recommendations, is available on the NTSB’s Website, www.ntsb.gov, under “Board Meetings.” The full report will be available on the Website in several weeks.