Which statement best defines Absolute Block?

Which statement best defines Absolute Block?

• A. A block that must not be occupied by more than one train.
• B. A cab signal used to indicate occupancy.
• C. A block that is used only for maintenance trains.
• D. A block that can be occupied by two trains if one is in authority.

Answer: (A)

Absolute Block is the rule that a block of track must not be occupied by more than one train at a time. Once a train enters and occupies a block, it remains occupied until the rear has cleared the block, and no other train may enter it until it is clear and proper authority is given. This arrangement is what keeps trains safely separated and prevents collisions by requiring exclusive use of each block. Cab signals and other occupancy indicators reflect that status, but they are tools for enforcing the rule, not the definition itself. The idea that a second train could enter if one already has authority or that maintenance trains can share the block would violate the one-train-per-block principle.

Absolute Block is the rule that a block of track must not be occupied by more than one train at a time. Once a train enters and occupies a block, it remains occupied until the rear has cleared the block, and no other train may enter it until it is clear and proper authority is given. This arrangement is what keeps trains safely separated and prevents collisions by requiring exclusive use of each block. Cab signals and other occupancy indicators reflect that status, but they are tools for enforcing the rule, not the definition itself. The idea that a second train could enter if one already has authority or that maintenance trains can share the block would violate the one-train-per-block principle.