What is block signaling?

• A. A system that divides track into sequential blocks with occupancy detection to control signal indications and train movement.
• B. A method where trains are signaled based on line-of-sight.
• C. A signaling arrangement that uses timetable data to authorize movement.
• D. A signaling system that operates without any sensors.

Answer: (D)

Block signaling is a safety method that splits the track into short sections called blocks and uses detectors to know whether a block is occupied. This occupancy information feeds the signaling system, which sets signals to indicate whether the next block is clear, holds, or requires a reduced speed, ensuring trains maintain safe separation. The key idea is real-time control: a train cannot enter a block that is occupied, so only one train can be in a block at a time, and the following train receives a signal based on the status of the block ahead. This approach relies on sensors such as track circuits or axle counters to detect presence on a block, not on what a driver can see visually or on fixed timetable timings.

Block signaling differs from line-of-sight signaling, where signals depend on what the driver sees or interprets rather than the actual occupancy of track sections. It also differs from timetable-based systems, which rely on predetermined schedules rather than current occupancy data. And it’s not sensor-less; sensors are essential to determine whether a block is occupied and to adjust signals accordingly.