SIGNALLING PRINCIPLES HOW R U GUYS ITS ALL ABOUT
- 1. Signalling Principles In Plain English (Reference to masculine gender also refers to the female gender!) Tony Howker March 2011
- 2. A system that Prevents collisions and derailments! A Definition of Signalling (The tool to Manage the Operation of the Railway)
- 3. Look what happens in a collision or derailment!
- 4. How does Signalling do this? A signalman – operator of the Signalling System, gives instructions to a Driver of a train. The Instructions started with Handsignals but then put signalmen controlled coloured lights or planks of wood on the top of poles and expected Drivers of Trains to obey their meaning!
- 5. Handsignal being exhibited by the Signalman. (He was called a policemen in those days – hence the nickname for a signalman was “Bobby”)
- 12. A Few Definitions I think that you know what I mean and you think I know what you mean – but just to be sure!
- 13. Definitions • Route • A section of railway line from a fixed signal to the next signal – may contain points or not – may continue past next signal if overlaps are provided Route Overlap
- 14. Definitions • Signal • A means of displaying an “Authority to Proceed” and the driver is aware of the limit of that Authority.
- 15. Definitions • Points • Facing • Trailing • A moveable section of the railway that allows trains to divert onto or converge from another section of railway Facing point complete with Facing Point Lock Diverting Lines Trailing point – Converging Lines
- 16. Definitions • Overlap • In the Rear of a Signal • In Advance of a Signal • An Overlap is a section of railway line beyond a stop signal that must be clear before a train can be given permission to approach that signal from the rear. Length often varies between a nominal distance and braking distance Overlap In Advance In the Rear
- 18. Definitions Normal & Reverse • These originally described the position of a mechanical lever in a frame and thus related to the position of points. When relating to signals they describe the signal being at Stop or Red. Nowadays Normal is a statement that the equipment or system is in a quiescent state awaiting a command to control signalling equipment. Pulling the lever controlling signals moved the signal to give proceed authority to the Train Driver. (Always assuming that the interlocking allowed the movement) This is the NORMAL position This is the REVERSE position
- 19. Definitions • Interlocking (Original) • Originates from the meaning to interlock between 2 or more levers in a mechanical frame 10 Worked by Lever 11 Worked by Lever To Move Lever 10 from “Normal” to “Reverse” – Lever 11 has to be “Normal”. If Lever 11 is “Reverse”, Lever 10 cannot be moved from the “Normal” position and therefore is Locked “Normal” in the lever frame. Hence the word “Interlocking” Worked by Lever 9 “Normal” Position of 11 points will allow a train to pass along the Main Line – The diagram shows the “Normal” lie of the points. If 11 points are “Reverse” then the points will allow a train to move from the Loop Line to join the main Line by moving Lever 9 to the “Reverse” position Loop Line Main Line
- 20. Definitions • Interlocking (Modern Definition) & Controls Can be done using relays, computers or a combination of both. • This is the name given to the Equipment and System that allows the signalling to be controlled in a safe manner and the information given to the Train Driver to also be correct and safe. The Interlocking also receives information from the trackside. Today the terms “interlocked by” and “controlled by” are synonymous and both could be replaced by “required by”. Interlocking TC A TC B TC C TC D TC E TC F TC G TC H 23 101A 101B 25 TC J Indications Controls Signalman Requests Diagram or VDU
- 21. The Main Principles Giving unequivocal permission to the driver that it is OK for him to proceed means that - •The line is clear of any other train or obstruction along this route to the limit of Authority •The Signalman will not alter the line or route as long as the authority is valid •If we withdraw the Authority to proceed, we will not be able to alter the line or route until the train that was given the authority has come to a complete stand
- 22. Principles for allowing a Main signal to show a proceed aspect • The line must be clear between the route entrance signal and the exit signal ahead • The overlap must also be clear • Any lines that converge should also be clear to the protecting signal • All points in the route must be set, locked and detected in the right position • Trailing points in the overlap at the exit signal must be locked and detected normal • The entrance signal of any directly opposing routes must be proved at Red and free of Approach Locking
- 23. Some more Definitions • Route Locking (Sometimes called Route Holding) • Approach Locking If we give permission to a train driver to proceed, we also need to maintain the route in front of the train whilst it passes through the route. This is called Route Locking. If we wish to withdraw this permission before the train has passed the entrance signal, (i.e. entrance signal replaced to Stop) we also need to maintain the route until we are sure that the train has either come to a stand or has passed through the route. This is called Approach Locking Entrance Signal 15 Exit Signal 19 TC AA TC BB TC CC 101 TC DD 102 TC EE After Signal 15 restores to Red after showing a proceed aspect for the Route from 15 to 19, the route remains locked in front of the train. This means that points 101 & 102 remain locked until the train has passed clear over them. This is called Route Locking or Route Holding
- 24. Approach Locking Before we discuss Approach Locking – a little piece of Physics! •Trains are heavy and travel at quite a reasonable speed and create substantial kinetic energy •Because this kinetic energy needs to be dissipated, braking to a stop means that trains cannot stop as quickly as cars or trucks – they need distance which also means time. •Therefore our trans cannot be driven “on-sight” as a car or truck can. All signals capable of showing a stop aspect need to have an advance warning signal at least “Braking Distance” before the stop signal. This is often known as a “Distant” signal. •So when our signalman withdraws a movement authority (i.e. he replaces a signal to red or stop) he cannot rely on the fact that the train driver will have enough time or distance to be able to bring his train to a stop at the red signal, especially as the warning (or distant) signal will have been showing an indication that stated that the next signal was at proceed. This means that the requirement to hold the route locked until the train has come to a stand must be carried out by “Approach Locking” •Approach Locking can only be released by proving the train is at a stand at the red signal or that the train has passed safely through the route which has remained locked even though the signal at the entrance to this route has been replaced to red in front of the train.
- 25. Approach Locking 15 A 3 A 2 A 1 When this signal at Red This signal shows Caution Braking Distance Braking Distance This signal shows Proceed at line speed This signal shows Red Signal 15 Cleared to Proceed This signal shows Proceed at line speed This signal shows Proceed at line speed This signal shows Red Signal 15 replaced to stop Train within Braking Distance and cannot stop before 15 Signal Route ahead of Signal 15 now “Approach Locked” – only released by Train at a stand at 15 signal (usually done via a timer having run – say 3 minutes), or train passing through route.
- 26. Further Principles Associated with Locking • Approach Locking • Route Holding • Before a signal can clear the approach locking must be proved as being applied so that it is available if required. • The same applies to route holding – it must be proved to be applied before the signal can clear to a proceed aspect.
- 27. Train Separation • The other Principle besides locking is Train separation. • This is achieved by only allowing one train at a time into a particular piece of railway line. This section of line is often called a Block – It may or not be equal to Braking Distance. (Probably longer) Block Block & Braking Distance Braking Distance Braking Distance & Block Braking Distance & Block Braking Distance & Block
- 29. In Plain Language We have just defined the fundamental principles of Signalling Interlocking Principles & Train Separation Principles
- 30. Interlocking Principles • No route can be established unless that route is free of any opposing or conflicting movements or locking • Any points within the route shall be free of locking or set in the required position • The route should be unoccupied by trains or other obstructions before the exit signal can be allowed to show a proceed aspect • Any points in the route shall be locked and detected in the required position • Any Overlap at the exit signal shall be clear of trains and any opposing or conflicting locking • Once a proceed aspect has been given to the driver it shall not be possible to alter the route • It shall be possible to withdraw the authority given to a driver (re-placing the entrance signal to stop) however it shall not be possible to alter the locked route until the train has come to a stand or has passed through the route • Finally before allowing a signal to show a proceed aspect to the driver, it must prove that the route ahead is locked and that the approach locking should be primed and ready to be activated.
- 31. Train Separation •Only one train shall be allowed in one section of line at a time (Block Signalling) •Trains need time and distance to brake to a stand from the allowed line speed – signalling should allow for preliminary caution signals and not force drivers to “drive on sight” like a car or truck
- 32. A few extra comments •You will note that I have kept to the basic Principles of Signalling, deliberately not differentiating between speed or route signalling or the aspects shown to a Driver. •Neither have I shown any principles for the application of any sort of Automatic Train Protection System. •The equipment used for detecting whether a line is clear or obstructed is outside the scope of signalling principles – hence the idea of “Plain English”
- 33. Remember who the Customer is for our Signalling