A long freight train carrying hazardous chemicals partially derailed and set fire near East Palestine, Ohio, on 3 February. It released hazardous chemicals into the surroundings and has raised concerns about possible health effects for residents. It has also left people wondering how a 3-kilometre-long freight train can come off of the rails like this.
鈥淵ou鈥檙e basically dealing with a big mile-long or more Slinky,鈥� says , a retired investigator for the US National Transportation Safety Board. 鈥淭he first thing they teach you in engineering school is the biggest problem in controlling a train鈥� is getting the train to stop and not getting that mile-long Slinky to kill you.鈥�
About 50 of the 150 cars in the freight train operated by Norfolk Southern Railway went off the tracks in a way that left many cars lying alongside each other almost perpendicular to the track. That suggests a 鈥渃atastrophic derailment鈥� where a broken component causes a train to derail 鈥渞eal quick and real sudden鈥�, says Quimby.
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What warning signs were there of trouble?
The National Transportation Safety Board has obtained videos showing potential mechanical issues on one of the rail car axles 鈥� the component connecting two train wheels on either end 鈥� that it played during a 5 February press conference.
The also reported that security cameras in Salem, Ohio, showed one of the passing train cars having a bright glow on its underside that was likely due to a malfunctioning and overheating axle. That was about 32 kilometres away from the site where the derailment occurred.
Railroad tracks typically have wayside detectors 鈥� also known as hot box detectors 鈥� located every 16 kilometres, on average, to check the temperature of axles on passing trains. An overheating axle is supposed to trigger a radio alert for the train crew and train dispatchers that indicates which axle is experiencing a potential problem, says Quimby.
The train passed one detector near Salem and another near East Palestine just before the derailment. The train crew told federal investigators that they received a detector alert shortly before derailment.
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How quickly can a freight train stop?
Once they got the alert, the train crew members said they initiated an emergency braking action for the freight train. But it can take a distance longer than the length of a train to come to a complete halt, says Quimby.
The standard braking system consists of compressed air in a train brake line that connects the locomotive to all the cars. When the engineer applies the brakes, the system releases air to reduce brake pressure and triggers a series of mechanical steps that push the brakes against the train wheels.
But the braking effect based on air pressure is nowhere near instantaneous. 鈥淚t鈥檚 going back to the first car and the second car in a relay 鈥� somewhat of a domino effect 鈥� towards the rear of the train,鈥� says Quimby. The entire process could take several minutes for longer trains.
The 150-car train involved in the derailment is more than double the length of an average freight train. In December 2022, the US found that the largest freight railroads have all started running longer trains such as this in an effort to improve efficiency.
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Can anything be done to prevent this in the future?
Newer electronic braking systems could potentially stop trains more quickly. But reporting from has highlighted how the US freight train industry has lobbied against federal efforts to require such advanced braking systems.
The National Transportation Safety Board plans to release a preliminary report on the incident within four to six weeks, and a final investigation report within 18 to 24 months.
