Absolute Permissive Block (APB) Signaling System built using an Arduino
APB are a form of Automatic Block Signal (ABS) systems, but provide protection for the front, as well as the rear as a traditional ABS system would.
- Track Segment - Independently controlled section of track that may only have a single occupant at a uniform speed. Must be able to provide occupancy and occupant direction
- Turnout - Track Segment that can move between a "main" and "divergent" state. When not in either the "main" or "divergent" state, the state is "impassable". Must be able to provide occupancy, occupant direction, and turnout state.
- Signal Block - Collection of track segments protected by a single signal.