Bloksignalisatie

Bloksignalisatie, or block signaling, is a railway traffic control method used to prevent collisions by dividing a railway line into fixed or dynamic sections called blocks. When a train occupies a block, the signal controlling the next block ahead is set to a restrictive aspect, ensuring only one train can occupy adjacent blocks at any time. The system relies on track circuits—electrical circuits that detect the presence of a train by the change in conductivity caused by its wheels—and/or axle counters that count wheels passing a point.

Historical development began in the late 19th century with the first mechanical block instruments operated by signalmen. The introduction of interlocking and automatic block instruments in the early 20th century allowed signals to be set and changed automatically, improving safety and efficiency. By the 1960s, electrical block signaling became widespread worldwide, and later digital and computer‑based implementations such as cab signalling and Automatic Train Control (ATC) systems further enhanced performance.

Operation of a block system requires continuous communication between trackside equipment and central or local control centers. If a block is occupied, the following block's signal is at danger, preventing a second train from entering until the block is cleared. In moving block or continuous‑protection systems, block boundaries are not fixed; the train’s actual position and braking distance determine signalling, allowing higher capacity and reduced headways.

Benefits of block signaling include proven safety over decades, simplicity, and robust fail‑safe characteristics. Drawbacks are limited capacity, especially on busy lines, and the need for comprehensive track instrumentation. Modern networks increasingly supplement or replace traditional block systems with European Train Control System (ETCS) Level 2 and beyond, which use continuous GPS‑based or balise‑based communication to achieve moving‑block operation while maintaining high safety standards.