JACKSON, Miss. (AP) - The site of a train-tour bus crash that killed four people in Mississippi has a troubling history of accidents, including two this year, local and federal officials said Wednesday.

National Transportation Safety Board member Robert Sumwalt said the crossing in Biloxi has a hump that has caused tractor-trailers to bottom out, and the federal agency is looking into whether the steep grade played a role in the crash Tuesday. The crossing has had at least 17 accidents involving vehicles and trains since 1976.

"It sounds like a lot," Sumwalt noted, saying investigators would compare the crossing with other similar ones.

A freight train smashed into a charter bus in Biloxi, Mississippi, on Tuesday, March 7, 2017, pushing the bus 300 feet down the tracks authorities said. Authorities worked for more than an hour to remove passengers, Biloxi Fire Chief Joe Boney said, taking the injured people to area hospitals and cutting through the bus's mangled body to extract the final two people. (AP Photo/Kevin McGill)

On Tuesday, a charter bus carrying dozens of tourists to Mississippi casinos became stuck on the railroad tracks for about five minutes before a freight train barreled into it, sending frantic passengers in all directions, witnesses said. About 40 people were hurt.

The cause of the crash is under investigation. Sumwalt said the agency's team would look into how long the bus was stuck, the history of the motor coach company and its driver, and whether or not the train's two-man crew could have done anything differently.

Some of the tourists from Texas were getting off the bus when the crash occurred, said Mark Robinson, a Biloxi native who saw the crash.

Body parts were "thrown everywhere," Robinson told WLOX-TV .

The train was traveling 26 mph - almost 20 mph less than the track's speed limit - when the crew put on an emergency brake about 510 feet from the bus, Sumwalt said. The train had slowed to 19 mph by the time it hit the bus. It pushed the mangled motor coach about 200 feet down the tracks.

Authorities said it took more than an hour to get everyone out of the wreckage. Two people had to be removed with metal-cutting equipment.

Mayor Andrew Gilich attended the NTSB news conference and said he had personally known people who had died at the crossing. He stressed that changes need to be made.

"As far as long-term improvements to this crossing and others in the city, I will continue to press for us to close crossings so that we can work with CSX to improve safety of others," he said in a statement posted on the city's website.

CSX spokeswoman Laura Phelps said the Biloxi area has a large number of crossing wrecks at least partly because there are so many railroad crossings, including 18 in a span of about 3 miles. She said she doesn't know whether the area has a higher rate of wrecks per crossing than other areas.

Sumwalt said the crossing is the responsibility of both the city and railroad company. CSX said creating a more gradual slope would be up to the city.

The crossing had a sign warning drivers of a low-ground clearance, as well as a bell, lights and crossing arms. There was one fatality each during accidents in 1983 and 2003 at the crossing in question.

In January, a Pepsi delivery driver's tractor-trailer became stuck at the same crossing. The driver bailed out and ran down the road to warn the engineer of an approaching freight train, but the train still plowed into the stranded semi and pushed it about 70 to 80 feet before stopping, the city said. No one was hurt.

"Almost every accident like this could be avoided," said David Clarke, director of the Center for Transportation Research at the University of Tennessee. "But we still keep having rail crossing collisions."

Killed Tuesday were Ken and Peggy Hoffman, two former administrators with the Lockhart school district south of Austin. Ken Hoffman, 82, worked for the district for decades and was an assistant superintendent. His 73-year-old wife was an elementary school principal.

Also killed were Clinton Havran, 79, of Sealy, Texas, and 62-year-old Deborah Orr.

The weeklong trip had started Sunday and was organized by a senior citizens' center in Bastrop, Texas, about 30 miles east of Austin.

The bus belonged to Echo Transportation of the Dallas area. Echo said it will cooperate with the investigation but declined to provide further details.

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Associated Press writers Jeff Amy in Jackson, Mississippi, and Jeff Martin in Atlanta contributed to this report.

Responders works the scene where a train hit a bus in Biloxi, Miss., Tuesday, March 7, 2017. A freight train smashed into a charter bus in Biloxi, Mississippi, on Tuesday, pushing the bus 300 feet down the tracks authorities said. Authorities worked for more than an hour to remove passengers, Biloxi Fire Chief Joe Boney said, taking the injured people to area hospitals and cutting through the bus's mangled body to extract the final two people. (AP Photo/Gerald Herbert)

Biloxi firefighters assist injured passengers after their charter bus collided with a train in Biloxi, Miss., Tuesday, March 7, 2017. Biloxi city spokesman Vincent Creel says emergency responders were still removing injured people from the bus more than 30 minutes after the crash. (John Fitzhugh/Sun Herald via AP)

Emergency personnel assist injured passengers after their charter bus collided with a train in Biloxi, Miss., Tuesday, March 7, 2017. Biloxi city spokesman Vincent Creel says emergency responders were still removing injured people from the bus more than 30 minutes after the crash (John Fitzhugh/Sun Herald via AP)

In this photo made from video and released by WLOX-TV, Authorities pull passengers off a bus after colliding with CSX freight train, Tuesday, March 7, 2017, in Biloxi, Miss. Biloxi city spokesman Vincent Creel says emergency responders were still removing injured people from the bus more than 30 minutes after the crash. (WLOX-TV via AP)

A freight train smashed into a charter bus in Biloxi, Mississippi, on Tuesday, March 7, 2017, pushing the bus 300 feet down the tracks authorities said. Authorities worked for more than an hour to remove passengers, Biloxi Fire Chief Joe Boney said, taking the injured people to area hospitals and cutting through the bus's mangled body to extract the final two people. (AP Photo/Kevin McGill)

Responders works the scene where a train hit a bus in Biloxi, Miss., Tuesday, March 7, 2017. A freight train smashed into a charter bus in Biloxi, Mississippi, on Tuesday, pushing the bus 300 feet down the tracks authorities said. Authorities worked for more than an hour to remove passengers, Biloxi Fire Chief Joe Boney said, taking the injured people to area hospitals and cutting through the bus's mangled body to extract the final two people. (AP Photo/Gerald Herbert)

A freight train smashed into a charter bus in Biloxi, Mississippi, on Tuesday, March 7, 2017, pushing the bus 300 feet down the tracks authorities said. Authorities worked for more than an hour to remove passengers, Biloxi Fire Chief Joe Boney said, taking the injured people to area hospitals and cutting through the bus's mangled body to extract the final two people. (AP Photo/Kevin McGill)

Responders works the scene where a train hit a bus in Biloxi, Miss., Tuesday, March 7, 2017. A freight train smashed into a charter bus in Biloxi, Mississippi, on Tuesday, pushing the bus 300 feet down the tracks authorities said. Authorities worked for more than an hour to remove passengers, Biloxi Fire Chief Joe Boney said, taking the injured people to area hospitals and cutting through the bus's mangled body to extract the final two people. (AP Photo/Gerald Herbert)

Responders works the scene where a train hit a bus in Biloxi, Miss., Tuesday, March 7, 2017. A freight train smashed into a charter bus in Biloxi, Mississippi, on Tuesday, pushing the bus 300 feet down the tracks authorities said. Authorities worked for more than an hour to remove passengers, Biloxi Fire Chief Joe Boney said, taking the injured people to area hospitals and cutting through the bus's mangled body to extract the final two people. (AP Photo/Gerald Herbert)

Responders works the scene where a train hit a bus in Biloxi, Miss., Tuesday, March 7, 2017. A freight train smashed into a charter bus in Biloxi, Mississippi, on Tuesday, pushing the bus 300 feet down the tracks authorities said. Authorities worked for more than an hour to remove passengers, Biloxi Fire Chief Joe Boney said, taking the injured people to area hospitals and cutting through the bus's mangled body to extract the final two people. (AP Photo/Gerald Herbert)

Responders works the scene where a train hit a bus in Biloxi, Miss., Tuesday, March 7, 2017. A freight train smashed into a charter bus in Biloxi, Mississippi, on Tuesday, pushing the bus 300 feet down the tracks authorities said. Authorities worked for more than an hour to remove passengers, Biloxi Fire Chief Joe Boney said, taking the injured people to area hospitals and cutting through the bus's mangled body to extract the final two people. (AP Photo/Gerald Herbert)