What is the speed limit if PTC fails but the Cabs work in ABS territory?

In the context of Positive Train Control (PTC) systems, if PTC fails but the cab signals are operational within Automatic Block Signal (ABS) territory, the speed limit generally becomes 79 mph. This is due to safety protocols that maintain higher speeds when there are operational cab signals, which provide a level of oversight and safety even in the absence of PTC functionalities.

The cab signals inform the engineer of track conditions and enforce compliance with speed restrictions, thus allowing for a higher maximum allowable speed. Maintaining this limit ensures efficient train operations while still prioritizing safety, as long as the cab signals are functioning correctly.