JACKSON, Miss. (AP) — A train crash into a tour bus that killed four in Mississippi last year stemmed from the railroad and the city failing to improve an unsafe rail crossing, federal safety regulators concluded Tuesday.

The March 2017 crash also injured 38 Texas tourists when their bus got stuck on a steep Biloxi rail crossing and was hit by a CSX Corp. freight train.

The National Transportation Safety Board found that the probable cause of the crash was “the failure of CSX Transportation and the city of Biloxi to coordinate and take action to improve the safety of the Main Street grade crossing, a high profile vertical crossing on which motor vehicles were known to ground frequently.”

Meeting in Washington, the NTSB also issued 11 recommendations for preventing future crashes that focus on railroads and governments doing more to evaluate rail crossings that are so steep they pose safety risks.

Biloxi spokesman Vincent Creel said the city would review the findings “to see what additional measures we can take to improve the safety at crossings.” However, Creel said, the city doesn’t have enough money to rebuild its 29 crossings, all of which are steeper than current road-design guidelines.

A CSX spokeswoman didn’t immediately respond to a request for comment.

The board concluded that the tour bus driver’s decision to take a scenic route along U.S. 90 and use a commercial GPS mapping system played no role in the accident. Although the GPS system contained information about the high-profile crossing, the driver wouldn’t have realized how steep the back side of the crossing was until it was too late, investigators said.

Problems have existed at the Main Street crossing for decades but seem to have become worse after CSX maintenance raised the track elevation in 2014, the NTSB said.

The board recommended that railroads, traffic engineers and regulators develop guidance for when states and localities should ban trucks, buses and other at-risk vehicles from high-profile crossings. Biloxi banned trucks, buses and recreational vehicles from the Main Street and some other crossings after the crash.

The board also recommended that railroad and highway groups develop specific criteria to determine when an existing crossing is so unsafe that it should be rebuilt, closed or have its risks “comprehensively mitigated.”

NTSB Chairman Robert Sumwalt said he feared that with railroads, state transportation agencies and local governments all sharing responsibility for rail crossings, it might not be clear who is in charge.

“Every entity might think that a specific hazard is somebody else’s responsibility,” Sumwalt said.

Board staff members said the current standard warning signs, which show a low-boy trailer striking a railroad track, may be of “negligible” value. Sumwalt suggested drivers of buses and other trucks may not perceive those signs as applying to them.

Findings emphasize better communication, saying the Mississippi Department of Transportation should do more to monitor crossing safety statewide, the city of Biloxi should share records of vehicles getting stuck with the state and railroads should share records of vehicles getting stuck with all states. The NTSB also recommends that railroads and transportation agencies coordinate on any track maintenance with the potential to increase track elevation.

The NTSB also renewed a recommendation that safety briefings be mandatory on all motor coaches. It also recommended that drivers show passengers how to operate emergency exits.

Tour bus driver Louis Ambrose Jr. gave a safety briefing to most riders, but after the Biloxi crash, passengers at the rear of the bus were unaware of an emergency door there and didn’t know how to open it. Firefighters cut it open.

Three people who died were evacuating down the front stairs when they were thrown out of the bus and run over by the bus and train. A fourth died of internal bone fractures he experienced while standing in the aisle during the impact.