Which system primarily helps prevent train derailments due to excessive speed?

The Automatic Train Stop (ATS) system plays a crucial role in preventing train derailments that can occur due to excessive speed by automatically initiating braking actions if certain speed thresholds are exceeded. The ATS system is designed to monitor the train's speed in real time and compare it against predetermined limits for various track sections.

In situations where a train is approaching a section of track that requires a reduced speed—such as curves, stations, or work zones—ATS can automatically apply the train's brakes if the engineer fails to respond to the warning signals. This automated intervention can effectively avert potential derailments caused by excessive speed, enhancing safety on the rail network.

While the other systems mentioned do contribute to overall operational safety, they serve different primary functions. For instance, Automatic Train Control (ATC) encompasses a broader range of functionalities, including speed regulation but is not solely focused on derailment prevention. The Dead Man's Switch ensures that the train will stop if the operator is incapacitated, but it does not directly regulate speed. Lastly, the Emergency Brake System is in place for immediate stopping in emergencies, but it does not provide ongoing monitoring and control of speed in normal operation. Thus, ATS is specifically designed to prevent excessive speed derailments effectively.