Selection Of Signals Click on Left mouse Button to advance.

1. TPWS Selection Of Signals Click on Left mouse Button to advance.

2. TPWS Selection The following presentation describes the process whereby signals are assessed to determine which will require provision of TPWS in order to comply with the regulations. This presentation does not currently address the assessment for TPWS provision at other sites apart from Signals & Buffer Stops .

3. TPWS Type Of Line TPWS is required on railway lines normally used by passenger trains or to protect such lines. TPWS is not required to be provided on freight-only lines, or lines which may be used occasionally as diversionary routes for passenger train. TPWS is required at junctions with passenger routes, including the exit from sidings and depots, the protecting signal shall be assessed for fitment as any other passenger line.

4. TPWS Type Of Signal The regulations require provision of TPWS at all signals at which a train is required to stop including stop boards. Red lights on buffer stops, and signals provided for shunting purposes only (e.g. position light, miniature arm, miniature colour light, disc signals), as well as limit of shunt signals or signs, are excluded from this requirement.

5. TPWS Stop Aspect Provision of TPWS is proposed for signals capable of displaying a stop aspect

6. TPWS Absolute Block Areas In a number of areas absolute block working is in operation between signal boxes. The layout of signals(the majority of which are mechanical semaphores) in these areas does not generally follow colour light signalling practise, stop signals being spaced at less than braking distance apart Selection of signals for TPWS will however follow the same rules as colour light signals in multiple aspect signalling installations.

7. TPWS Points & Crossings A fundamental consideration affecting the provision of TPWS is whether the signal protects any pointwork on which a conflict could occur between a train passing the signal at Danger without authority and another train legitimately traversing a signalled route. In order for TPWS to offer the same level as protection as is provided by the interlocking, this consideration must extend as far as the end of the full overlaps of the next signals ahead, corresponding to the section of line to be proved clear of obstruction before the signal may display a proceed aspect.

8. TPWS Signals Limiting BI- Directional Moves Where a signal is provided to mark the limit of movement along a section of line signalled to allow movements to take place against the normal direction of traffic (e.g. to allow a train to enter a station platform and then depart in the opposite direction), the signal , and signals protecting it shall be provided with TPWS. (Note this does not apply to Limit of Shunt signals or signs.)

9. TPWS Signals Limiting BI- Directional Moves Intermediate signals in fully BI- directional signalled sections which do not protect pointwork or other conflicts can be considered as fulfilling an equivalent function to automatic or plain line signals, and so do not require the provision of TPWS

10. TPWS Emergency Crossovers TPWS is required at all signals protecting possible points of conflict. A specific exception is made for emergency crossovers, normally controlled by a Ground Frame, used only in an emergency for engineering purposes.However the definition of an emergency crossover can be vary from place to place and requires a certain amount of local knowledge. Therefore it is better to fit Ground frame controlled crossovers with TPWS unless a specific instruction is given proving its emergency status.

11. TPWS Diverging Routes Where a signal protects pointwork where routes only diverge, such as at the entrance to a loop line signalled for one direction of running, there is no possibility of a conflict occurring. Note how a rear end collision is not considered.

12. TPWS Layout Protection In certain cases, the arrangement of the track layout in advance of a signal may be as to provide ’acceptable’ mitigation of the effects of SPAD without TPWS being fitted. If a layout is arranged with facing points which can divert a train passing a signal at danger away from a conflict with a signalled route, or with trap points or a derailer that would arrest an unauthorised movement, this protection could obviate the requirement for TPWS

13. TPWS Layout Protection Layout protection must protect against signalled and unsignalled moves. (Technical Instr. No6) Example: A train can be waiting at Signal A without a signalled move. A spad on signal B can result in a conflict at Signal A if the points are not auto normalising B A

14. TPWS Platform Starting Signals The possibility of a ‘start-away’ SPAD must be considered if there is a conflict ahead of a platform starting signal.

15. TPWS Level Crossing Protection Where a signal protects only a level crossing on otherwise plain line TPWS will not normally be provided LEVEL CROSSING

16. TPWS Flowchart A TPWS selection flowchart is available which can guide you through the process of verifying signals for the provision of TPWS, it can be found in the RT line spec RT/E/S/10137

17. TPWS Example 1 A B O/L TPWS required on both A & B signals as a SPAD on either of these signals could lead to a conflict

18. TPWS Example 2 A B C TPWS required on both A & C signals as a SPAD on either of these signals could lead to a conflict, B signal has layout protection provided by crossover. Again check the crossover has auto normalisation.

19. TPWS Example 3 A B O/L TPWS required on signal B. Signal A has trapping protection therefore TPWS is not required.

20. TPWS Example 4 A B C D TPWS required on A & D signals, layout protection diverts SPAD signals B & C into lines which has traffic in the same direction, note how double SPAD’s are not taken into account.Again, Layout protection must be proved, see the control tables.