Officials believe the bus became stuck on the elevated crossing
before the train hit, killing four and injuring dozens of others, Cecilia Dobbs Walton, a spokeswoman for the city of Biloxi, Mississippi said.
Three other long vehicles have gotten stuck in that intersection in the last three years alone. In two of those cases, a train crashed into the vehicle.
That history has caught the National Transportation Safety Board's attention.
"We're very interested in factors such as that. What is it about this intersection?" NTSB member Robert Sumwalt said ahead of the panel's investigation Wednesday.
At issue is the railroad crossing at Main Street -- known as a hump crossing because the tracks are on the crest of a slope. A driver at such a crossing goes up an incline, crosses the level tracks and then goes down an incline.
This kind of hump can catch the undercarriage of a vehicle or trailer if the vehicle is long enough and the ground touching the front and back tires is low enough.
Here are the three other incidents since 2014:
January 5, 2017: Pepsi truck crash
A Pepsi delivery truck became stuck on the hump as its driver tried to cross the tracks, Biloxi officials posted on the city's Facebook page at the time.
The driver exited the truck minutes before a train slammed into it, CNN affiliate WLOX
reported. No one was injured.
March 12, 2016 : Tour bus stuck, but not hit
In a scene eerily similar to Tuesday's incident, a tour bus carrying 28 passengers became stuck at the crossing, officials posted on Facebook.
But in this instance, there was no crash. The passengers left the bus, and no train came through while the vehicle was across the tracks, city spokesman Vincent Creel said.
August 28, 2014: Train hits tractor-trailer
A tractor-trailer became stuck on the Main Street crossing. A train struck the vehicle, injuring a railroad employee, according to the Federal Railway Administration.
What about safety measures?
The intersection has a sign on either side, warning drivers of a "low ground clearance." The graphic on the sign shows a trailer caught on the tracks.
The sign is just a caution to drivers, said George Gavalla, a former associate administrator for safety at the Federal Railroad Administration.
"It doesn't really tell you which vehicle is going to clear and which won't. It doesn't prohibit any vehicles from going over," Gavalla said. "It just says, 'Be careful; there's a hump crossing.' "
The Main Street crossing also has flashing lights and crossing gates, CSX spokesman Gary Sease said.
Though no causes of Tuesday's crash have been determined, Sumwalt said the NTSB is "very interested in measuring that hump."
The NTSB intends to make recommendations to help prevent such crashes when the probe is finished. But the agency will issue a recommendation sooner if they find any "imminent hazard," Sumwalt said.
Sumwalt said the responsibility for the intersection is shared by the CSX railroad company and the city government.
Creel said the Main Street crossing is not the only crossing in the city "that has an issue with the grade." The slopes have been that way for years and no specific grade improvements were under consideration before Tuesday, said Creel, the city spokesman.
But the mayor had proposed closing six of the city's 29 crossings, in part so that resources can be devoted to improving other ones, Creel said. The proposal, which the city council has yet to take up, did not include the Main Street crossing.
"I will continue to press for us to close crossings so that we can work with CSX to improve the safety of other crossings," Mayor Andrew "FoFo" Gilich said Wednesday
The crash that changed Biloxi's maps
Before Tuesday, the Main Street crossing had 16 train-vehicle crashes since 1976, including two deaths, Sumwalt said. At least six of those wrecks involved vehicles that were stalled or otherwise stopped on the tracks, according to the NTSB and the Federal Railroad Administration.
One of those 16 wrecks left its mark on maps of Biloxi.
Running parallel to the track is Esters Boulevard. It was named after Michael Esters, the city's first African-American city councilman, following his death, Creel said.
Esters was killed at the Main Street crossing. A train struck his moving vehicle, FRA records show, on March 23, 1983.