In East Palestine, Ohio, very preliminary speculation suggests that the derailment was the result of a hot bearing. But there are 389 documented ways for trains to derail.
On February 3, a Norfolk Southern Railroad train derailed in East Palestine, Ohio. Thirty-eight total cars derailed, including some carrying hazardous materials. In the heat of the moment, workers on the scene decided to burn some chemicals in an effort to reduce their environmental impact. People in East Palestine—a town of about 4,700—have since reported some health complications that may be linked to the chemicals and the fire.
After thorough investigations and scientific studies are conducted, experts and organizations will weigh in on the disaster and related health hazards in the coming days and weeks. Today, we aren’t certain what caused the derailment.
But one thing is clear: the public has a general lack of education on trains, which are complicated machines with a variety of parts that must be maintained and inspected regularly. There are train accidents and derailments regularly—there were over 1,000 reported derailments in the United States in 2021 alone—and no amount of maneuvering will reduce those numbers to zero.
A train is the umbrella term for at least one locomotive and at least one car, Bryan Schlake—a professor at Penn State University at Altoona, which offers a unique program for undergraduates who want to study railroad engineering—tells Popular Mechanics. And the power source of these trains is partly electric.
“All our freight moves by diesel electric power,” he explains. “A diesel engine is powering an electric alternator, and that energy is used to supply traction motors. It’s just an electric signal that’s powering electric motors under each of the powered axles on the locomotive. It’s more like a hybrid car, because it’s got electric motors powering the axles.”
The industry has considered making technology that recovers more of the energy from braking, which is something hybrid cars already do: the friction created by braking charges the battery. But, Schlake says, diesel fuel is so energy-dense that it’s hard to incentivize the industry to include a change that will make a relatively small difference; trains carry thousands of gallons of diesel at a time, and can go 1,000 miles without a refuel. They’re more like ships than automobiles in the sense that momentum can help them travel faster than seems possible for their size.
There are just seven major freight railroads that cover all of North America on “Class I” lines—soon to be six, with the merger of two of them. As in other industries, rolling mergers have consolidated hundreds of separate companies into just a few, what Schlake labels an oligopoly: “two Canadian railroads, four large U.S. Class I railroads, [and] Kansas City Southern, which is Kansas down into Mexico.”
When it comes to trains, ownership is not as straightforward as it seems. Railroads own the locomotives, and the railroads own the rails; but individuals or companies usually privately own the actual rail cars as a form of passive income. Only about 25% of rolling stock is owned by the railroads, and virtually no tank cars. (You can even buy working train cars online!)
Perhaps more surprising, major railroads are subject to common carrier laws. That means regulated groups—like freight carriers, internet service providers, and airlines—can’t turn down freight that meets all the legal requirements, and they can’t discriminate against anyone seeking freight service who is otherwise not objectionable. Trains, like trucks, carry cargo ranging from raw materials like timber and liquid chemicals to fully manufactured consumer goods. There are dozens of types of cars to accommodate such goods.
In the case of East Palestine, Ohio, the train was carrying hazardous materials. How those materials are defined, how they are carried and protected, and whether or not local officials are warned about them is all a complicated part of the common-carrier subject.
✅ Vital Context: The leadership of the Federal Railroad Administration is politicized. During Democratic administrations, this person is typically from the world of public transit or other civic employment; while during Republican administrations, they are typically from private railroad company leadership.
The bipartisan Federal Railroad Administration (FRA) is part of the United States Department of Transportation, and maintains robust statistics on trains. “Running on almost 140,000 route miles, the U.S. freight rail network is widely considered the largest, safest, and most cost-efficient freight system in the world,” the FRA explains. “Compared with other major modes of transportation, railroad owners invest one of the highest percentages of revenues (19 percent) to maintain and add capacity to their system, spending nearly $25 billion annually.”
“About 40 percent of all ton-miles are being transported by rail. So bulk, heavy freight that’s being moved across the country,” Schlake says. That number dropped to about 30 percent in 2020, probably because of the pandemic.
In order to be reported, a derailment must cause a certain amount of financial damage or have casualties in the form of injuries or death. The 1,087 reported derailments in 2021 don’t include very minor derailments that fall beneath the minimum threshold requirements, and that figure also doesn’t include all train accidents. A train may hit a car, but not derail.
A derailment can mean just one car off the rails by a few inches, or, as in East Palestine, Ohio, 38 cars that are completely off the rails and heavily damaged. Solving smaller derailments can be as simple as sending the train’s crew out to build a little ramp from ballast and wood in order to get the car back into alignment on the track. In more complicated derailments, special services use bulldozers to lift and reposition the cars. And in a case like East Palestine, cars may be destroyed if they’re damaged enough.
The Rail Equipment Accident database categorizes derailments using 389 “cause codes” to help experts study trends. Almost all of these causes will have a nonzero likelihood each year. Multiply that out by the massive quantity of annual freight train travel in the United States, track conditions, and the materials these trains are carrying, and even the least likely outcomes end up happening sometimes.
David Clarke is a retired transportation researcher who previously headed the Center for Transportation Research at the University of Tennessee. A bunch of things can happen just to the tracks, he explains. One major cause are broken or damaged rails. “Broken rails and welds are more highly correlated with rail accidents where the train was moving at speed down the track,” Clarke says. “There are a lot of other things that could cause a derailment with regards to track condition, [like] the rails not at proper spacing or at improper elevations or out of alignment.”
The wear-and-tear on railroad tracks is not morally loaded. Your car needs a regular oil change and, once in a while, a new serpentine belt or alternator. How you address these problems can have consequences, like cars that cause crashes due to poor maintenance. But the problems, themselves, are just the consequence of using machinery for heavy duty jobs over a sustained time period.
Railroad tracks are typically made of ballast (like gravel), wooden or concrete ties or beds, and steel rails. Rails can split horizontally or develop cracks through their diameter. There are welds and bolts that can all go bad over time. A section of rail may fragment and break apart into pieces after a winter storm. All these issues can create short gaps in the rail’s continuity.
Trains run at speed, and may make it over short gaps without derailing, because momentum plays a part. But the longer the gap, or if the gap is in a situation like a banked curve of track, the more likely the train is to derail. Even a minor derailment—one that can be repaired by the train’s crew, as explained above—can cause enough damage that it needs to be reported. Extremely heavy train cars may be dragged along by momentum, and this can damage the tracks and ties below.
Tracks are Clarke’s specialty, but they’re far from the only cause of derailments. “Derailments occur for a number of possible reasons,” he explains. “One possible reason is something goes wrong with the track. Another is something goes wrong with the equipment that rolls on the track. And the third is the train, through some human factors error in operation of the train, develops internal forces that push it off the track.”
So ... What Caused the Train Derailment in East Palestine, Ohio?
In East Palestine, Ohio, very preliminary speculation (ahead of a formal government report that will likely take a couple of weeks to complete) suggests that the derailment was the result of a hot bearing. This is the portion of the end of each rail car’s axle that rests on the assembly of the wheels. In a rail car, there are typically no electrical parts at all; everything is mechanical and powered by momentum, air, and other forces generated by the locomotive.
Brakes have been discussed a lot in the wake of the East Palestine derailment, because trains are hard to stop even in the case of an emergency. Schlake says that, based on the incomplete information he and his colleagues have at this time, he doesn’t believe the braking itself was involved in the derailment. If the train started to derail because of a bad bearing, braking is the right response. Although it can sometimes happen, it would be unusual for anything about braking itself to derail a train.
✅ How Do Brakes Work on a Long Train? There are traction motors on the locomotives, themselves, where the “engine” is that drives the train; these brakes create resistance that slow the entire train, starting with the locomotive. And then there are air brakes on the rail cars, which are triggered without power and are entirely mechanical. Air pressure is used to decide how much the train needs to slow down, using feedback that’s generated from the locomotive and passed down the entire train through air pipes. These are rigid pipes on the train cars and air hoses between the cars.
But, Schlake says, trains have grown longer in recent decades. Just in terms of physics, that means air is taking longer to reach the very end of the train to trigger the air brakes on those cars. In response, some have suggested electronic brakes that the railroad companies have resisted due to higher costs. Instead, they’ve begun adding more locomotives to the trains, themselves. If you’ve ever seen a long train that had locomotives at each end, this may be why. They can even insert locomotives in the middle of the train, shortening the distance to air brakes even more. Schlake says that this process can make up about 75 percent of the ground between traditionally used air brakes and the costly electronic brakes.
The locomotive industry is filled with technologies for detecting defects, because trains are critical for transporting goods. Clarke says this equipment, like a broken rail detection system, is good at spotting things like cracks in rails and other defects before they cause the rail to fracture or split. “It’s certainly well worth using rail detection where the trains are moving along over the track at more than just a walking-type speed,” Clarke says.
Of course, nothing is perfect. “Sometimes the detection equipment misses, because it’s not 100 percent effective in finding things,” Clarke says. But, he explains, "[T]he larger the defect, the better the systems are at finding it. If rail inspection is conducted properly, the chances of finding all large defects are excellent." For example, many detectors work using ultrasound. If a signal bounces back through a rail too quickly, that can mean it's split—the sound is traveling a shorter distance through the broken rail. When a defect reaches a certain size or severity threshold, that's when railroads take action.
Detectors installed at 15- to 20-mile intervals along the tracks can also monitor hot bearings. The vast majority are infrared, measuring the temperature of bearings or wheels as they fly by. There are also a few acoustic detectors. These work by listening for a shrill sound made when bearings start “running dry,” a sign that they’re rapidly wearing out and even melting. “When a detector goes off, trains typically slow down, and if the measurement is severe enough, they will apply the brakes and come to a stop on the mainline,” Schlake says.
In the weeks to come, new information will continue to come to light about the derailment in East Palestine, Ohio. But Clarke, for his part, does not believe this derailment is exceptional based on what has been made public so far. He worries that politicians will seize on the moment to apply a policy Band-Aid that is not appropriate for the industry. With heightened awareness of derailments around the country since February 3, it’s easy to see how that could happen.
Caroline Delbert is a writer, avid reader, and contributing editor at Pop Mech. She's also an enthusiast of just about everything. Her favorite topics include nuclear energy, cosmology, math of everyday things, and the philosophy of it all.
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