SELECTION OF SITES FOR TPWS FITMENT

1. First job in the design process is therefore to assess whether TPWS is required to be fitted at a signal or not.

2. NR/SP/SIG/10137 – “TPWS – Selection of Signals and Other Locations for Provision of Track Sub System”.

3. NR/SP/SIG/10138 – Transmitter Loop Requirements And Positioning.

4. Flow Chart.

5. All decisions will be recorded in TAMAR (TPWS Asset Management and Reporting) database.

Where to Provide TPWS?

1. At Signals

2. At Stop Boards

3. At Buffer stops

4. At PSRs/TSRs

Which signals are to be fitted with TPWS?

Where a signal protects a number of geographical routes ,and one or more of these routes leads to a possible conflicts ,either with in routes or with in an overlap of a signal ahead ,the signal must be equipped with TPWS.

Which signals are to be fitted with TPWS?

1. Type of line:

Signals on lines normally used by passenger trains.

Generally not provided on signals which are on freight lines but ORAM can consider a signal on any line which  has high risk factor.

2. Type of Signals:

To be provided on all stop signals including stop boards.

Which signals are to be fitted with TPWS?

1. A flow chart provided in Appendix A of RT/E/S/10137 is used to to determine the requirements of TPWS at signals.

2. Selection at each step is a straight forward Yes/No decision.

3. Where an outcome has reached that indicates that TPWS should not be fitted ,an exclusion code shall be recorded.

Where not to fit TPWS?

1. At Intermediate signals on bi-directional lines.

2. At Signals protecting  level crossings only.

3. Where a signal protects a move up to limit of shunt signal or sign, TPWS shall not be provided.

4. Where the signal and all trains operating past the signal under normal circumstance are provided with an alternative train protection system ,approved by HMRI as compliant with regulations

Whether OSS is required at Signal?

There are 6 main conditions under which an OSS is not required at a signal:

1. The Safe Overrun Distance is adequate.

2. The signal is a platform starter at a terminal or turn round platform with speeds generally below 25 mph.

3. There are points in the Overlap of the signal beyond and Warning controls are in place.

4. Certain signals (other than Home) in Absolute Block, Electric Token Block & Tokenless Block signalled areas.

5. Stop Boards in RETB signalled areas.

6. Stop Boards in NST and NSTR signalled areas.

Adequate Safe Overrun Distance

Safe Overrun Distance Required

OSS Loop Positioning Calculations For Signals

OSS Loop Positioning Calculations For Signals

Calculation of Trigger loop position

7.4.3 OSS Trigger Loop nominal position

The nominal distance from the signal to the leading edge of the OSS Trigger Loop (in the direction of travel) shall be determined from Table 5

Adjustment to Gradient

STEP 3: ADJUST NOMINAL POSITION FOR GRADIENT

The nominal position is adjusted by adding / subtracting a figure, dependent on the steepest falling gradient (or shallowest rising gradient) within 400 metres in rear of the signal. In the most extreme case, the nominal position can be extended by 75 metres, to 425 metres in rear of the signal.

Table6- Gradient Correction Distance

Calculation of Arming loop position

Final Adjustments

STEP 5: FINAL ADJUSTMENTS

There may be constraints due to the non-permitted loop positions already discussed, which prevent the arming or trigger loops going in the calculated positions. In this case, the loops may be moved by a maximum of 25 metres in either direction, before settling on a final position.

Note: if this adjustment is by more than 12 metres, the Trigger loop position will fall into a new 25 metre band in Step 4, and so the loop separation will need to be re-calculated too.

TPWS+ Requirements and Positioning

• To improve the level of protection at certain signals, TPWS+ can be used which consists of one additional OSS to provide train protection for trains travelling at speeds in excess of 75mph, up to a nominal 100mph (see Figure 11). The additional OSS is referred to as OSS+.