Module TW1 Section 48 (Issue 20, December 2024) introduced some changes to the use of the warning horn.
You must only use the horn as much as is necessary to give an effective warning or to make sure safe working takes place.
To give a warning of your train approaching
Both tones if available
To give an urgent warning of immediate danger
Long blast.
Train in distress
Continuous series of long blasts.
When passing a whistle board
Low tone if available.*
To give a warning of a train movement
Short blast. Use the soft setting or depot whistle if available when in a depot or siding, or when entering a shed or building.
To sound a local or special code
Follow local or company instructions.
*Note ASLEF Circular No. 046/2025 which states that: "ASLEF continues to strongly recommended that drivers obey Rule 48.3 and sound the horn as a warning and at any other time you consider necessary, and advises all drivers to use a two-tone warning at all whistle boards until that rule is changed."
To give a warning of your train approaching
You must sound the horn (both tones if available) to warn anyone who is on or near the line on which you are travelling.
To give an urgent warning of immediate danger
You must sound a long blast of the horn to give an urgent warning to warn the driver of another train in danger or anyone who is on or dangerously near the line who does not either acknowledge your warning by raising one arm above the head, or appear to move clear out of the way of the train.
Train in distress
You must give a continuous series of long blasts of the horn as the 'train in distress' warning.
When passing a whistle board
You must only sound the horn when passing a whistle board between 0600 and 2359, except in an emergency or when anyone is on or near the line. You must sound the horn on the low tone if available as you pass the whistle board, and not before.*
If you are making a wrong direction movement, you must sound the horn when passing a whistle board that applies to movements in the right direction.
To give a warning of a train movement
You must sound a short blast of the horn to give a warning of a train movement or on starting your train when making a movement within a possession.
When the train movement is at a depot or siding, or when entering a building or shed, you must sound a short blast of the horn using the soft setting or depot whistle if available, or follow your company instructions.
General
You must sound the horn at any other time you consider necessary or when specified in your company instructions.
*Note ASLEF Circular 475 dated 16/8/18 which states that drivers may choose to use a two tone horn at whistle boards, for safety reasons, on the basis that it falls under the category of "at any other time you consider necessary."