What type of signal is required before proceeding into Working Limits?

Before proceeding into Working Limits, the requirement for an Approach Signal is crucial. An Approach Signal is designed to advise a train of an upcoming condition that necessitates that attention must be paid. Specifically, when a train is about to enter working limits, it is essential for safety reasons that the crew is alerted to the potential need to reduce speed or be prepared to stop, as working limits often involve maintenance activities or other hazards.

In this context, the Approach Signal serves as an indication to the train crew that they should be prepared for further signals and to proceed with caution. It ensures that the crew is aware that they are transitioning into an area with potentially restricted or controlled conditions. This aligns with safety protocols that are crucial in managing train operations near maintenance zones or other areas where work crews might be present.