page_title: Signalling block system
section_title: Automatic block signaling
hierarchical_section_title: Signalling block system / Block signalling methods / Automatic block signaling
caption_attribution_description: English: Distant signal of Japan, between Sukenobu station and Hachiman station of Enshu Railway Line. 日本語: 遠州鉄道鉄道線八幡駅（西鹿島方）にある遠方信号機（右）。中央が場内信号機。奥左に見えるのが出発信号機である。
context_page_description: Signalling block systems enable the safe and efficient operation of railways by preventing collisions between trains. The basic principle is that a route is broken up into a series of sections or "blocks". Only one train may occupy a block at a time, and the blocks are sized to allow a train to stop within them. That ensures that a train always has time to stop before getting dangerously close to another train on the same line. The block system is referred to in the UK as the method of working, in the US as the method of operation, and in Australia as safeworking.
  In most situations, a system of signals is used to control the passage of trains between the blocks. When a train enters a block, signals at both ends change to indicate that the block is occupied, typically using red lamps or indicator flags. When a train first enters a block, the rear of the same train has not yet left the previous block, so both blocks are marked as occupied.
context_section_description: Automatic block signaling uses a series of automated signals, normally lights or flags, that change their display, or aspect, based on the movement of trains past a sensor. This is by far the most common type of block system As of 2018, used in almost every type of railway from rapid transit systems to railway mainlines. There are a wide variety of systems, and an even wider variety of signals, but they all work in roughly the same fashion.
  Like the manual block systems outlined above, automatic systems divide the route into fixed blocks. At the end of each block, a set of signals is installed, along with a track-side sensor. When a train passes the sensor, the signals are triggered to display the "block occupied" aspect on the signals at either end of that block. In most systems the signals do not immediately return to the "block empty" aspect when the train leaves, instead there is some sort of mechanical delay that retains the block occupied aspect, or more commonly, presents a "proceed with caution" aspect.
caption: Vertical colour light signal on the Enshū Railway Line in Japan
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