Absolute block working started to be implemented from the end of 1874, and in the following few years recognisable signal boxes were constructed across the system, with interlocking.
22.
Historically, the two express tracks were an absolute block, that is, there was no signal control between one end of the tracks near Sixth Avenue and Kings Highway.
23.
"' Absolute block signalling "'is a British system is used on double or multiple lines where use of each line is assigned a direction of travel.
24.
The dangers of working single track railways had long been recognised, and all sorts of safeguards ( in addition to absolute block working ) were supposed to be in place.
25.
The line from the intermediate block home signal to the home signal of the next signal box on the same line in the same direction of travel is the absolute block section.
26.
The current signalling is based on a two, three, and four aspect colour light system using the absolute block principle; permissive block may only be used in certain limited circumstances.
27.
The absolute block system controls the safe movement of trains in the block section, and no more than one train may ever enter the section at once, other than in exceptional circumstances.
28.
The absolute block system came into use gradually during the 1850s and 1860s and became mandatory in the United Kingdom after legislation in 1889 following a number of accidents, most notably the Armagh rail disaster.
29.
The absolute block system does not replace the use of any other form of signalling, such as fixed signals, hand signals, or detonators ( and, in fact, usually relies on fixed signals ).
30.
Before 2015, Three Bridges signalling centre controlled the route between Keymer Junction and Plumpton and Brighton to Falmer where Lewes Power Box takes over until Southerham Junction, from which absolute block signalling takes over through to Hastings.
