Automatic Block Signaling, or ABS, is a block system that consists of a series of signals that divide a railway line into a series of blocks and then functions to control the movement of trains between them through automatic signals. ABS operation is designed to allow trains operating in the same direction to follow each other in a safe manner without risk of rear end collision while reducing costs and increasing capacity from previous manual block systems that required human operators. The automatic operation comes from an ability to detect if blocks are occupied or otherwise obstructed and then convey that information to approaching trains. The term "Automatic" in ABS refers to the operation of the system without any outside intervention and contrasts with more modern traffic control systems that require external control to establish a flow of traffic.
Read more about Automatic Block Signaling: Basic Operation, Replacement
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