A track extending through yards and between stations that must not be occupied without authority or protection. Main Track A fixed signal at the entrance of a block that governs trains entering and using that block. Block Signal A notice containing track bulletin restrictions and other conditions affecting train movement. General Track Bulletin A series of consecutive blocks governed by block signals, cab signals, or both. The signals are activated by a train or by certain conditions that affect the block use. Automatic Block Signal System (ABS) Two or more main tracks that are used according to the timetable. Multiple Main Tracks Good Faith Challenge Rule 1.4.1A Good Faith Challenge A. Right to Challenge Federal Regulations have provisions that allow an employee the right to challenge a directive which, based upon the employee's good faith determination, would violate a railroad operating rule relating to: