What is the maximum speed a train can move when cab signals fail in ABS territory, if granted under Rule 556?

In ABS (Automatic Block Signal) territory, if cab signals fail, Rule 556 dictates the operation of trains under those conditions to ensure safety. The established maximum speed limit when cab signals are inoperative is set at 59 mph. This speed limit is designed to allow trains to proceed with caution while protecting against potential hazards that could arise from the loss of automated signals.

The rationale behind this speed limit includes considerations for adequate stopping distance, reaction time of crew members, and the safety of other trains operating in the same territory. In such scenarios, the train is typically required to operate at a reduced speed, allowing for better control and the ability to respond safely to any unexpected conditions ahead.

Other speed limits provided in the options do not align with the regulation specified in Rule 556 for cab signal failures in ABS territory. The correct answer reflects the regulatory framework to promote safe railway operations under adverse signal conditions.