What action should be taken if a train is approaching a red signal?

When a train approaches a red signal, it is critical for the safety of all involved to immediately stop the train. A red signal indicates that the train must halt to either wait for clearance to proceed or to prevent a potential collision with another train or obstacle on the line. Stopping at a red signal adheres to safety protocols that are in place to manage train movements effectively and prevent accidents.

Immediately obeying the signal by coming to a stop allows the engineer time to assess the situation ahead, ensuring that they can follow the necessary procedures to proceed safely once given clearance. This action is vital not only for the safety of the train crew and passengers but also for other trains on the network.

While slowing down and preparing to stop is important in general train operations, the immediate action prescribed is to stop completely at a red signal, solidifying the necessity of vigilance and adherence to signaling protocols in railway operations. The other options suggest responses that could endanger safety by not ensuring a complete stop at the critical signal.