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[[File:Block instrument.jpg|300px|thumb|right|A typical block instrument.]]'''Absolute Block ''' is a method of signalling for controlling the passage of trains over a [[Double track|double track railway]]. This 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 the principal terminus, normally London. The Absolute Block system ensures that only one train may be in a section 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 signal box|Bewdley North]] and [[Bewdley South signal box|Bewdley South]] signal boxes. The original Severn Valley Railway was built as a single track railway, and was mainly worked using [[Single line working using tokens | tokens]], although short sections of double track at stations such as [[Stourport]] were worked using Absolute Block.  

Unlike working on single linesBefore the introduction of block systems, where the time interval system was used to maintain separation between trains can . A following train would be allowed to depart after a specified time interval, on the assumption that both would proceed in either directionat a similar speed. This meant that should the first train come to a stand, each there was no absolute safeguard to prevent a rear end collision other than the vigilance of the engine crew. Use of the two lines in Absolute Block work unisystem was made mandatory on passenger-directionally. The presence of two carrying lines allows two trains to proceed in different directions at the same time1889<ref>Wikipedia</ref>. Trains usually travel ==Absolute Block on the left hand side, similarly to how cars always drive on Severn Valley==The only section of the left in current SVR controlled this way is the UKmain lines between [[Bewdley North signal box|Bewdley North]] and [[Bewdley South signal box|Bewdley South]] signal boxes. Each The original Severn Valley Railway was built as a single track is identified by its normal direction of trafficrailway, with the two directions being named "Up" and "Down"was mainly worked using [[Single line working using tokens | tokens]], with "Up" generally being defined as the line leading towards London. There may only be one train on each although short sections of double 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 timestations such as [[Stourport]] were worked using Absolute Block.