Absolute block signalling
（重定向自Block apparatus）
![A block instrument set to its default position of](/Images/godic/202501/01/Block_instrument5110.jpg")
![British Railways standard block instrument showing Line One's status on top (for the departing train), Line Two's status in the middle (for the approaching train), with the handle at the bottom](/Images/godic/202501/01/Block_Instruments-95110.JPG")
![Close-up of the commutator, tapper and bell mechanism](/Images/godic/202501/01/Block_Instruments-115110.JPG")
![Tyer's single stroke signalling bell](/Images/godic/202501/01/Block_Instruments-25110.JPG")
Absolute block signalling is a British signalling scheme designed to ensure the safe operation of a railway by allowing only one train to occupy a defined section of track (block) at any time. This system is used on double or multiple lines where use of each line is assigned a direction of travel.