A line block is requested by the engineering official in charge, and granted by the Divisional Railway Manager. The station master of a station adjacent to the affected block section receives a copy of the line block order from the DRM, and he decides when to implement the line block. In busier sections the Section Controller is also involved in deciding when to impose the line block. In some cases, if the traffic disruption is extensive and the block is required for longer than usual, necessitating much rerouting and rescheduling of trains, the block is termed a megablock (or 'mega block').
The simplest is a line block, or traffic block, which blocks a particular track (or tracks) when repair or construction work...
more... has to be carried out on the permanent way, points, crossings, interlockings, OHE, signalling equipment, etc. Such blocks are sometimes also called possession blocks (since the permanent-way staff 'take possession' of the tracks).