Understanding Train Speed After Removing Coaches

When a train is running at a speed of 120 miles per hour (mph) and one or more coaches are removed, the speed of the engine alone is a complex interplay of various mechanical and operational factors. This article aims to explain these factors in detail to provide a comprehensive understanding of the train behavior under such circumstances.

Factors Influencing Train Speed

In conventional diesel-electric locomotives, the throttle does not regulate track speed in the manner of a vehicle's accelerator. Instead, it controls the generated power over a fixed rotational speed range. This setup is largely digitized and managed by multiple unit (MU) control systems. Additionally, the engine governor ensures that the engine maintains its speed despite varying loads on the generator/alternator.

The speed at which a train moves is determined by the balance between the effective train resistance and the tractive effort produced by the locomotive. If a coach is removed, the train's resistance decreases, leading to a new equilibrium speed that is generally higher than the original speed. This new speed will not exceed the maximum speed the locomotive can achieve when operating light engine.

Situation Analysis: Removing Coaches One by One

When coaches are removed one by one, the train's resistance, or drag, decreases accordingly. This reduction in resistance allows the locomotive to maintain or increase its speed, but the extent of this change depends on various factors. Removing empty coaches generally results in a minimal speed increase, approximately within a 5-10 mph range. However, if the coaches are filled with people or heavy cargo, the impact on the train's speed will be more significant.

Braking Mechanisms and Full Train Stopping

When the last coach is removed, the train's speed will decrease due to the reduced load. However, the train might not come to an immediate halt. The train must first be disconnected from the air hoses, which supply the air pressure for the brake system. Once the air hoses are disconnected, the automatic brakes will engage, and the train will come to a complete stop. The process of disconnecting the air hoses and separating the coaches requires careful coordination to ensure safety and prevent accidents.

Safety and Operational Considerations

It is crucial to understand the complete process of decoupling a train, including disconnecting air hoses and separating coaches. If not properly managed, the sudden release of train pressure can cause significant safety issues. Modern trains are equipped with advanced braking systems designed to provide gradual deceleration and stop the train safely.

The process of disconnecting and decoupling typically involves:

Disconnecting the air hoses to the remaining coaches.

Unlinking the couplings or box connectors between coaches.

Once these steps are completed, the train will automatically apply the brakes, causing the train to decelerate and eventually come to a complete stop at 0 km/h.

Conclusion

The speed of a train after the removal of one or more coaches is influenced by the interplay between train resistance and tractive effort. While the throttle and governor play key roles in maintaining the locomotive's power, the actual speed will vary based on the load and condition of the removed coaches. Safety procedures are critical, and modern braking systems ensure a controlled and efficient decoupling and stopping process.