WASHINGTON, D.C. — The National Transportation Safety Board (NTSB) has recommended that motorcoach interiors be designed with improved flammability requirements and improved emergency exits, and that event data recorders be installed on large buses.

The recommendations resulted from the investigation of the April 2014 truck-motorcoach collision in Orland, California, in which 10 people were killed.

In the crash, a 2007 Volvo truck-tractor operated by FedEx Freight Inc. crossed a 58-foot-wide median, struck a 2013 Nissan Altima passenger car, and then collided head-on with a 2014 Setra motorcoach. The motorcoach was transporting high school students and chaperones on a trip to visit a college.

The truck and motorcoach drivers were killed, along with eight motorcoach passengers — five students and three chaperones. Thirty-seven motorcoach passengers and two occupants of the passenger car were injured.

Investigators were unable to determine why the truck crossed the median, but they ruled out truck and motorcoach driver experience, licensing and training, alcohol and drug use, mechanical factors and weather as possible causes of the crash. Likewise, the agency found no evidence that the truck driver was experiencing distraction or fatigue, or that he intentionally crossed into opposing traffic.

“The investigation brought to light the difficulty of getting out of a burning motorcoach,” NTSB Chairman Christopher Hart said. “It is unacceptable for anyone who survives a crash to perish in a post-crash fire because the exits were too hard to find or too difficult to use.”

According to NTSB, the investigation revealed inadequacies in the fire performance standards for commercial passenger vehicle interiors, Federal Motor Vehicle Safety Standard (FMVSS) 302. The flammability testing under FMVSS 302 involves a small-scale fire source, such as those that might be caused by matches or cigarettes, which NTSB said differ drastically from the actual common causes of bus fires.

The board also found that neither the motorcoach driver who initiated the trip nor the relief driver gave a safety briefing or played the prerecorded safety briefing that the company had provided, and many passengers struggled to locate and open the emergency exit windows. At least two passengers died because they could not exit the motorcoach before succumbing to asphyxiation due to inhaling smoke from the fire.

According to NTSB, a pre-trip safety briefing or a video about evacuation could have expedited the evacuation process and possibly saved lives and mitigated injuries. Also, Hart said that neither the truck-tractor nor the motorcoach had event data recorders, which impeded the investigation of the crash’s cause.

As a result of the investigation, the NTSB issued safety recommendations for commercial passenger vehicles that address fire performance standards; pre-trip safety briefings; improving vehicle design to facilitate evacuations; requiring the development of minimum performance standards for event data recorders in trucks and large buses; and requiring event data recorders to be installed in these vehicles.

The recommendation on requiring event data recorders, which NTSB has issued before, includes school buses. It specifies that those systems for school buses should record the status of flashing red lights, among other factors.

To view NTSB’s findings, the probable cause and all recommendations, go here. The full report will be available on the NTSB website in several weeks.