Train derailment refers to the situation in which a train leaves the rails during operation. Although modern railway systems are designed with high safety standards, derailments can still occur under certain conditions.
Understanding why trains derail and the different types of derailments helps explain the factors that affect railway safety.
Why Trains Normally Do Not Derail
Under normal conditions, trains are able to stay securely on the rails mainly because of the design of train wheels.
Train wheels are equipped with flanges, which are the raised edges located on the inner side of the wheel. The flange structure helps guide the wheel along the rail and prevents the wheel from moving off the track.
The inner side of the wheel tread is slightly larger than the outer side. During operation, the interaction between the two rails and the wheelset creates lateral forces that help keep the wheels properly aligned with the rails.
The wheel flange plays two important roles:
Guiding the wheelset along the rail
Preventing the wheel from leaving the rail
Railway standards require strict limits for wheel flange wear. If the flange becomes excessively worn and exceeds the allowable range, the risk of derailment increases. In such cases, the wheel flange must be re-machined to restore the standard profile.
Railway tracks are also carefully designed according to train speed, curve radius, track curvature, and axle load. These factors determine the rail alignment and track smoothness to ensure trains remain safely on the rails.
On curved tracks, the outer rail is raised higher than the inner rail, a design known as superelevation. This structure helps balance the centrifugal force generated when trains pass through curves.
Types of Train Derailments
Wheel Climb Derailment
When a train moves through a curve at low speed and the angle of attack between the wheel and rail is positive, the vertical load on one side may decrease while lateral force increases. In this situation, the wheel flange may gradually climb up the rail during rolling, causing derailment.
Wheel Slide Derailment
When the wheel-rail angle of attack is negative, the wheel may rotate while sliding upward along the rail surface under sufficient lateral force. This type of derailment is known as slide derailment.
Jump Derailment
Jump derailment usually occurs when trains are running at higher speeds. Strong lateral vibration or sudden lateral impact forces can cause the wheel to momentarily jump off the rail.
Gauge Widening Derailment
Excessive lateral force between the wheel and rail may cause the rail to move outward, leading to track gauge widening. When the gauge becomes too large, the wheel may fall inside the rail and derail.
Main Causes of Train Derailment
Natural Disasters
Natural disasters can damage railway infrastructure. Even with modern monitoring systems for strong winds or earthquakes, sudden events such as landslides, falling rocks, or debris flows may still affect railway safety.
Maintenance Issues
Railway systems require continuous inspection and maintenance. If problems are not detected in time, they may increase the risk of derailment. Examples include track gauge exceeding allowable limits, track structure damage, switch failures, or obstacles on the railway line.
Operational Violations
Improper operation may also lead to derailments. These include train overspeed, excessive braking, or failure to follow signal instructions.
Human Interference
Human activities can also affect railway safety, such as placing dangerous objects on the railway, collisions between road vehicles and trains, or unauthorized construction near railway lines.
Conclusion
Train derailments can occur due to a variety of factors, including natural events, infrastructure problems, operational errors, and human interference.
However, modern railway systems rely on strict engineering standards, regular maintenance, and operational control to reduce the risk of derailment. As a result, railways remain one of the safest and most reliable modes of transportation.
