Absolute Block is a method of signalling for controlling the passage of trains over a double track railway. This system ensures that only one train may be on each track in a section at any given time. The only section of the current SVR controlled this way is the main lines between Bewdley North and Bewdley South signal boxes. The original Severn Valley Railway was built as a single track railway, and was mainly worked using tokens, although short sections of double track at stations such as Stourport were worked using Absolute Block.
Overview
Unlike working on single lines, where trains can proceed in either direction, each of the two lines in Absolute Block work uni-directionally. The presence of two lines allows two trains to proceed in different directions at the same time. Trains usually travel on the left hand side, similarly to how cars always drive on the left in the UK. Each track is identified by its normal direction of traffic, with the two directions being named "Up" and "Down", with "Up" generally being defined as the line leading towards London. There may only be one train on each track in a section at each time, which means that trains proceeding in different directions (and hence different tracks) can occupy the same section at the same time.