On an ascending grade while operating a DP train, the brake valve shows 'Out' for the flow display. What would happen during a loss of radio communication?

On an ascending grade while operating a DP train, the brake valve shows 'Out' for the flow display. What would happen during a loss of radio communication?

• A. The system would automatically reestablish communications.
• B. The DPU would return to idle, possibly causing a break in two or a string line derailment.
• C. The train would slow to a stop safely.
• D. The lead locomotive would take control automatically.

Answer: (B)

When radio communications are lost in a distributed power setup, the system defaults the trailing units to a safe state because they can no longer receive authority from the lead. Seeing the DPU flow display as Out means the DPU isn’t receiving control data, so the DPU will go to idle to prevent uncontrolled propulsion. On an ascending grade, that idle DPU reduces the overall traction along the train. The lead locomotive may still be trying to pull, but the trailing unit is no longer contributing propulsion, creating an imbalance of pulling forces. This can put excessive stress on couplers and between sections of the train, increasing the risk of a break in two or a string-line derailment.

When radio communications are lost in a distributed power setup, the system defaults the trailing units to a safe state because they can no longer receive authority from the lead. Seeing the DPU flow display as Out means the DPU isn’t receiving control data, so the DPU will go to idle to prevent uncontrolled propulsion.

On an ascending grade, that idle DPU reduces the overall traction along the train. The lead locomotive may still be trying to pull, but the trailing unit is no longer contributing propulsion, creating an imbalance of pulling forces. This can put excessive stress on couplers and between sections of the train, increasing the risk of a break in two or a string-line derailment.