The failure of CSX and the city of Biloxi, Mississippi, to mitigate known safety hazards at a grade crossing is the probable cause of a 2017 fatal crash at the crossing, the National Transportation Safety Board (NTSB) announced yesterday.

Four people died March 7, 2017, when a chartered ECHO Transportation motorcoach grounded on the “high profile” grade crossing in Biloxi was struck by a CSX freight train. The four killed were among the 49 passengers on the motorcoach, NTSB officials said in a press release.

Although the CSX engineer saw the stranded vehicle and applied emergency braking, the train struck the coach at 19 mph.

No one on the CSX train was injured.

The grade crossing had an “unusually high vertical profile,” which put trucks and buses at risk of being “grounded” on the tracks, NTSB officials determined.

Three years before the accident, there were 23 known vehicle groundings there. Although the city and CSX were aware of the number of “safety-critical events,” neither acted to mitigate the hazard, NTSB officials said.

“This tragedy was preceded by numerous unheeded warnings in the three years leading up to it,” said NTSB Chairman Robert Sumwalt. “They came in the form of known groundings of other vehicles at the very same grade crossing where the fatal crash occurred. Warnings call for action.”

Inadequate guidance from the Federal Highway Administration on how to mitigate risks associated with high vertical profile grade crossings contributed to the crash, the NTSB determined.

The board recommended that high-profile grade crossings have clearer, less ambiguous signage so that drivers of all types of vehicles can better determine if their vehicle could safely traverse the crossing.

In addition, the NTSB made 11 new safety recommendations to the following: the Federal Highway Administration, the Federal Railroad Administration, the Mississippi Department of Transportation, the city of Biloxi, the American Association of State Highway and Transportation Officials, the American Railway Engineering and Maintenance-of-Way Association, the Association of American Railroads, the American Short Line and Regional Railroad Association and all Class Is.

The final report will be available in several weeks. Investigator presentations, findings probable cause and safety recommendations are available here.