A train derailment occurs when one or more wheels of a train leave the rails, causing cars to slide off track, tip over, or pile up. It sounds dramatic, but the vast majority of derailments are low-speed incidents in rail yards that cause little damage and no injuries. The smaller percentage that happen on main tracks at higher speeds are the ones that can turn catastrophic, especially when hazardous materials are on board.
How Wheels Leave the Rails
Train wheels are designed to stay locked onto rails through a combination of weight, speed, and a small lip called a flange that rides along the inner edge of each rail. Derailment happens when the forces acting on those wheels overwhelm this system. The Federal Railroad Administration identifies several distinct processes that cause it: wheelclimb, wheel lift, rail rollover, gauge spreading, and outright component failure.
Wheelclimb is the most studied. It happens when strong lateral (sideways) forces push a wheel upward against the rail at an angle, causing the flange to ride up and over the top of the rail instead of staying seated against it. This is more likely on curves, where the physics of a heavy train naturally push outward. Friction between the wheel and rail can either resist or accelerate the process depending on the angle at which the wheel meets the rail.
The other mechanisms are more straightforward. Rail rollover means the rail itself tips under pressure. Gauge spreading means the two rails move apart, widening the gap beyond what the wheels can span. Wheel lift is exactly what it sounds like: one side of the wheelset loses enough downward force that it rises off the rail entirely. And component failure covers everything from a cracked rail to a snapped axle.
Most Derailments Are Minor
The word “derailment” conjures images of overturned tanker cars and burning wreckage, but the reality is far less dramatic in most cases. About 74% of all freight rail derailments happen in low-speed rail yards, where trains typically move at around five miles per hour. At that speed, a wheel slipping off the track usually means minor property damage, no injuries, and no real impact on the surrounding community. Common examples include cars bumping off track during a shoving movement or a missed coupling.
Railroads are legally required to report any instance of even a single wheel leaving the rail as a derailment. They also must report any single event causing $12,400 or more in damage to track or equipment. This means the official derailment count captures everything from a barely noticeable yard incident to a major main-track disaster. In 2024, Class I railroads (the largest freight carriers) reported 793 derailments total. Roughly 74% were in yards and 26% on main-line track. Of that 26% on main lines, only five resulted in injuries (all non-fatal), and six involved a hazardous materials release.
What Causes Main-Track Derailments
The more serious derailments, the ones on open track at higher speeds, tend to stem from a handful of root causes. Track defects are a leading factor: broken rails, misaligned joints, or gauge problems that develop over time from heavy use and weather. Equipment failures, particularly overheated wheel bearings, are another major cause.
The 2023 East Palestine, Ohio derailment is a well-known example of bearing failure. A National Transportation Safety Board investigation found that a wheel bearing on a hopper car overheated and eventually caused the axle to fail. Wayside detectors, which are sensors placed along the track to monitor bearing temperatures, did not flag a warning until the train passed over a detector in East Palestine, by which point the bearing was already on the verge of catastrophic failure. The axle broke, and 38 cars derailed in the center of the small town.
Human factors also play a role. Excessive speed on curves, signal violations, and improperly secured switches have all contributed to derailments. So has deferred maintenance on both track and rolling stock.
The Hazardous Materials Problem
Freight trains routinely carry chemicals, fuels, and industrial materials that are perfectly safe inside sealed tank cars but extremely dangerous when released. When a derailment ruptures those cars, the consequences extend well beyond the crash site.
East Palestine illustrated this vividly. The Norfolk Southern train was carrying hazardous materials including vinyl chloride, a chemical used to make plastics. After the derailment, responders conducted a controlled burn of several tank cars to prevent uncontrolled explosions, sending a massive plume of smoke into the air. The National Institute of Environmental Health Sciences launched a research response to assess exposure to volatile organic compounds in the air and water. Researchers collected air and water samples from homes in the area and took blood samples from residents to evaluate both immediate and long-term effects on the liver and other organs from vinyl chloride exposure.
The contamination wasn’t limited to air. Chemicals entered local waterways and seeped into groundwater, requiring years of monitoring and cleanup. Private drinking water wells in the surrounding area needed ongoing testing to ensure safety.
What Cleanup and Recovery Cost
Major derailments carry staggering price tags. Norfolk Southern estimates it will spend more than $1 billion to address the East Palestine disaster. The U.S. Department of Justice reached a settlement valued at over $310 million, which covered only the federal claims. On top of that, the company had already spent roughly $780 million in environmental response costs.
The settlement broke down into specific obligations: an estimated $235 million for past and future cleanup, $25 million for a 20-year community health program including medical monitoring and mental health services, $15 million for a decade of groundwater and surface water monitoring, another $15 million for private drinking water well testing over 10 years, and $6 million for waterway restoration projects. Norfolk Southern also paid a $15 million civil penalty for Clean Water Act violations. These figures don’t include private lawsuits, lost property values, or the broader economic damage to local businesses.
How Derailments Are Prevented
Prevention relies on a layered system of inspections, monitoring technology, and operational rules. Wayside detectors placed along tracks measure wheel bearing temperatures, detect dragging equipment, and identify shifted loads as trains pass. When a detector flags an overheated bearing, the train crew is alerted to stop. The limitation, as East Palestine showed, is that detectors are spaced at intervals, and a bearing can deteriorate rapidly between checkpoints.
Track inspection is the other major line of defense. Traditionally, this has been done by human inspectors walking or riding along the rails looking for cracks, gauge problems, and worn components. Automated track inspection technology is increasingly supplementing this work. Track geometry measurement systems can detect defects in rail alignment and spacing with greater precision and consistency than visual inspection alone. Bipartisan legislation introduced in the U.S. Senate would require railroads to use both automated systems and human inspectors, with automated scans conducted at specified frequencies depending on how heavily a section of track is used.
Positive train control, a system that automatically slows or stops a train if the crew fails to respond to speed restrictions or signal violations, has been widely deployed on main-line tracks. It addresses the human-error side of the equation but does nothing to prevent derailments caused by equipment failure or track defects.