If a radio becomes inoperative en route on a light engine operated solely by the Engineer, what is the maximum speed they can proceed?

When a radio becomes inoperative while a light engine is being operated solely by the Engineer, the maximum permissible speed to which the train can proceed is 30 MPH. This regulation is in place to ensure safety and communication protocols are maintained, especially in areas where visibility or other operational challenges may arise.

The prescribed speed limit is designed to minimize risks associated with loss of communication equipment, as traveling at higher speeds may not allow enough time for the Engineer to react in case of an emergency or signal indication. This limit also accounts for situations where additional precautions may be needed due to the inability to communicate effectively with other railway personnel or systems.

In contrast, the other speed limits presented are lower and do not align with the established guidelines for a situation involving an inoperative radio, which is why they are not the correct choice.