American railway systems are working to push through technology that would make trains safer, but experts say it would be extremely difficult and costly to create a system that prevents accidents like the fiery crash in New York on Tuesday night that involved a commuter train and an SUV stuck on the tracks.
"This was a behavioral incident," Jeff Stagl, the managing editor of the trade publication Progressive Railroading, told NBC News via email. "People just don't heed crossing gates and signs as they should."
The crash in Valhalla, New York, happened after an SUV was stopped on the tracks when a railroad crossing gate came down on top of it. The driver got out and checked the car, got back in her vehicle and had started to drive forward when a Metro-North train hurtled into it, the Metropolitan Transportation Authority said.
Six people were killed and 12 were hospitalized in the Tuesday crash, making it the deadliest accident in the 32-year history of the Metro-North system. On Wednesday, a commuter rail train outside of Boston struck a vehicle but no one was seriously injured.
"It's a major issue in this country, and it is not being addressed," said Larry Mann, an attorney and leading rail expert who was the principal author of the Federal Railroad Safety Act of 1970.
A person or vehicle is hit by a train every three hours in the United States, according to the Federal Railroad Administration. (But overall, incidents like the Valhalla crash are declining: the FRA recorded 1,436 total commuter and freight train accidents in 2014, down 58 percent from 2004.)
"You can't stop these trains," Mann said. "If you have a 100-car freight train, which is not unusual, it takes over a mile to stop unless you want cars bunching up and derailing. Passenger trains don't have as many cars, but they go faster and are just as tough to stop. There's just no practical way to do it."
Not all experts agree that the crossing-collision problem is insurmountable, however.
"The answer is that we probably can at some point, but it’s not going to be cheap or at all simple," David Clarke, the Director of the Center for Transportation at the University of Tennessee, told NBC News.
There are some "glimmers of ideas" and "exploratory projects" that involve machine-vision cameras or sensors that could determine if something has entered a rail crossing, Clarke said. That "vision" question alone poses problems: Could a camera detect an object or person in a snowstorm? A downpour? At night? How would the system determine that an object is a crossing gate or a scurrying animal rather than a vehicle in trouble?
Even if the cameras or sensors could make these determinations, deploying that information in a useful way would be complex, Clarke said. The system would need to send communications to the train's controls, conductor and dispatcher -- and it would have to factor in the train's speed and distance from the crossing in any attempt to stop a collision.
"Plus, you don't want false warnings that slow down trains unnecessarily, causing even more problems to the system," Clarke said.
In an ideal scenario, Clarke and Mann both said, the rail system would get rid of crossings where the rails and roadways intersect -- but overhauling all that infrastructure and building new overpasses would be an extremely costly endeavor.
Despite the difficulties involved with creating a system that detects danger at a crossing, Clarke said he thinks that "down the road we'll be able to work it out." He suggested solutions could be built on top of positive train control (PTC): technology that, among other functions, automatically slows down a train if it's traveling above the speed it should be.
The PTC requirements -- drafted after the Chatsworth, California, train collision in 2008 that killed 25 people -- are meant to be enacted for a portion of the U.S. railway system by December 2015 but could be delayed until 2020.
In the meantime, Mann said, PTC is "a great program" but would not have stopped the Valhalla accident or others like it.
"[Crossing accidents] are a major problem, and unfortunately it hasn't been addressed adequately," Mann said. Still, he said, "this was a car on the crossing seconds before a train got there. What good can technology do for something like that?"