"We've been interested for some time in school bus safety," NTSB Vice Chairman Christopher Hart said at a news conference. "We're also interested in construction zone safety."
The accident happened Thursday on Interstate 44, about 40 miles from St. Louis. A semi cab slowed for road construction and was struck by a GMC pickup. Two buses carrying high school band students from southeast Missouri then slammed into that wreck.
The accident killed 15-year-old Jessica Brinker and the pickup driver, 19-year-old Daniel Schatz. Fifty-one students were treated for mostly minor injuries. Both bus drivers and the semi cab driver were also hurt.
The students from John F. Hodge High School in St. James were on their way to a day of fun at Six Flags St. Louis, and were about 10 miles from the amusement park when the wreck happened.
No charges have been filed in the wreck. Missouri State Highway Patrol Cpl. Jeff Wilson said it will be up to Franklin County prosecutors to decide that.
Hart said the NTSB isn't interested in pointing fingers. "We are here to determine the cause of the accident, not looking at blame," he said.
Among other issues, the NTSB will examine whether seat belts on the bus could have helped. He said investigators will also consider the possible benefits of accident-avoidance technology for commercial vehicles such as school buses that would warn drivers about impending slowdowns and automatically apply brakes.
Brinker was sitting in the back of the first bus to hit the wreck, the Highway Patrol said.
"She was the most funniest girl to be around! always rockin the knee high sock .... we love you Jessica R.I.P.," read a posting on Brinker's Facebook page Thursday night.
Kolby Griffith, 17, said he was chatting with friends on the second bus when it crashed, and that everything happened so quickly it was a blur.
"It was all very, very quick," Griffith said. "I was trying to get away, trying to get everyone away from the bus because I could smell gas."
Griffith was evaluated and released at SSM Cardinal Glennon Children's Medical Center in St. Louis, and was among about three dozen students called into a room at the hospital to be told about Brinker's death.
"There's a lot of pain," he said, choking back tears.
According to the Highway Patrol, a pickup truck driven by Schatz, a former reserve quarterback for the University of Missouri football team and the son of Republican state House candidate Dave Schatz, struck the back of a semi cab that had slowed approaching a construction zone.
The forward-most of the two buses carrying the students slammed into the back of Schatz's truck, then landed on top of it after it was rammed from behind by the other bus, Highway Patrol Cpl. Jeff Wilson said.
A huge crowd gathered Thursday evening for a hastily called prayer vigil at a middle school in St. James, a town of 3,700 residents 86 miles southwest of St. Louis that is known for its wineries.
"Anytime you have something like this, it is a big tragedy for a community," the town's mayor, Dennis Wilson, said earlier. He described the community as "one of those towns where you know just about everyone in town and know their kids," including the nearly 600 children who attend Hodge high school.
Joy Tucker, the superintendent of the St. James school system, said it was a "horrible, horrible day" for the community.
"We'll never get over this," she said.
Schatz was an all-state high school football player. He made the Missouri squad as a walk-on in 2009 but didn't get into a game, his father said. Daniel Schatz left Missouri and hoped to play alongside his older brother at Westminster College this fall.
Daniel was driving to Schatz Underground Inc., a family owned contracting business in Villa Ridge, when the accident occurred, said his father, who was supposed to be celebrating a big week after winning the Republican primary for a Missouri House seat on Tuesday.
He described his son as "a great kid."
Most of the students injured in the wreck had bumps and bruises and were expected to be fine, Wilson said.
Thirty-six people were originally taken to Cardinal Glennon and by late evening, all but one were released. Of six victims sent to St. John's Mercy Medical Center, five were released and one was transferred to St. Louis Children's Hospital. St. Louis Children's spokeswoman Jackie Ferman said that 16-year-old St. James girl was in stable condition.
Four other victims were taken with minor injuries to St. Clare Health Center in Fenton, Mo., a spokeswoman said.
The Highway Patrol said Friday the driver of the second bus Kelly McEnnis-Mullenix, 38, of St. James, and the driver of the semi cab, Michael Crabtree, 43, of Kearneysville, W.V., had moderate injuries. The other bus driver, 75-year-old Katherine Shackelford of St. James, had minor injuries.
Wilson, the patrol officer, said the driver of the first bus moved into the passing lane to give a distressed vehicle in the shoulder more room. She was checking her rearview mirror while returning to the right-hand lane when she noticed the first impact but could not stop in time, hitting the pickup. The second bus then rear-ended the first, vaulting the first bus onto the top of the pickup, which was crushed.
The buses were segregated by gender, with girls in the first and boys on the other, he said.
The pickup was barely recognizable in the tangled wreckage. Crews used a crane to lift the buses off of the crushed wreckage to clear the freeway, which was closed going eastbound for hours, backing up traffic for miles.
Associated Press writers Jim Suhr and Christopher Leonard in St. Louis, Chris Blank in Jefferson City, and Heather Hollingsworth and Bill Draper in Kansas City contributed to this report.