TPWS

Question 1

What does TPWS stand for?

Answer 1

Train Protection and Warning System

Question 2

What is the purpose of TPWS?

Answer 2

Initiate an emergency brake demand, where TPWS equipment is fitted, if a train has:
1. Passed a signal at danger without authority.
2. Approached a signal at danger too fast.
3. Approached a permissible speed reduction too fast.
4. Approached a Buffer Stop too fast.

Question 3

Is TPWS designed to prevent a SPAD?

Answer 3

No, TPWS is intended to reduce the consequence of a SPAD by preventing the train from reaching the conflict point beyond the signal.

Question 4

Where is TPWS fitted?

Answer 4

1. Stop signals, and some Stop Boards, on passenger lines protecting crossings or converging junctions.
2. Stop signals on non-passengers lines protecting crossings of, or convergence with, a passenger line.
3. Stop signals where conflicting movements could take place at the overlap of the stop signal ahead.
4. On approach to Buffer Stops at the end of passenger platforms.
5. On approach to some permissible speed reductions.

Question 5

What does TSS and OSS stand for?

Answer 5

Train Stop System
Overspeed Sensor System

Question 6

How far in advance of a Buffer Stop are TPWS OSS normally located and at what speed will they trigger a brake demand?

Answer 6

65 metres.
Speeds greater than 10mph.

Question 7

When would an OSS be placed in advance of a PSR reduction?

Answer 7

Where the linespeed is 60mph or more and the reduction is at least one third.

Question 8

When positioning TPWS track equipment what 4 things are taken into consideration?

Answer 8

1. Train braking characteristics.
2. Attainable speed of trains on approach.
3. Distance from the stop signal to the conflict point.
4. Gradient of the line.

Question 9

When are the following energised:
1. TSS at a stop signal.
2. OSS approaching a stop signal.
3. OSS approaching a PSR reduction.
4 OSS approaching a Buffer Stop.

Answer 9

1. When the signal is at danger.
2. When the signal is at danger.
3. Always.
4. Always.

Question 10

What are the two transmitters of a TPWS in order?

Answer 10

Arming loop & trigger loop.

Question 11

List 5 TPWS equipment components fitted to a train.

Answer 11

1. TPWS receiver.
2. TPWS control panel.
3. AWS/TPWS acknowledgement button.
4. TPWS temporary isolation switch.
5. TPWS full isolation switch.

Question 12

On an OSS what does the distance between the arming and trigger loops influence?

Answer 12

The set “trigger” speed.

Question 13

On a standard TPWS control panel identify the different button/indicators and describe what they mean.

Answer 13

Brake demand (red circle)
Off = no TPWS brake demand.
Flashing = TPWS/AWS has initiated a brake demand that Driver has not yet acknowledged.
Steady = Driver has acknowledged TPWS/AWS brake demand.

Temporary isolation/fault (yellow circle)
Off = TPWS is working.
Flashing = TPWS fault.
Steady = TPWS is temporarily isolated.

Train stop override (yellow square)
Off = Train stop override not active.
Steady = Train stop override active.

Question 14

How long will the Train Stop override button override the TPWS?

Answer 14

Approx 20 seconds.

Question 15

When would the Train Stop Override button extinguish?

Answer 15

After 20 seconds or after the train has passed over the TSS.

Question 16

When responding to an unsolicited brake application why is it important to carefully check the TPWS control panel?

Answer 16

No audible warning will accompany a TPWS brake demand so Driver must check the Brake Demand light to see if it is flashing.

Question 17

How would a driver acknowledge a TPWS brake demand?

Answer 17

Pressing AWS/TPWS acknowledgement button.

Question 18

How long after a TPWS brake demand will the brake demand light extinguish and train brakes release?

Answer 18

60 seconds after the brake demand.

Question 19

What additional 4 buttons are provided on an enhanced TPWS panel instead of brake demand?

Answer 19

SPAD
Overspeed
AWS
Brake release

Question 20

What may cause a TPWS fault during a self-test when the cab desk is opened?

Answer 20

Receiver is located above an active loop.

Question 21

On an advanced TPWS control panel how are TPWS brake demands acknowledged and how does this differ from standard control panels?

Answer 21

Driver presses the SPAD, overspeed or AWS buttons to acknowledge the brake demand instead of the AWS/TPWS acknowledgement button.

Question 22

When would a Driver need to use the AWS full isolation switch?

Answer 22

Where there is a fault with the system or the AWS receiver is located directly above the magnet and it is not possible to driver from the other end.

Question 23

When managing TPWS DOTE what difference is there between AWS and TPWS response?

Answer 23

The max 40mph restriction during poor visibility does not apply.

Question 24

When proceeding on Absolute Block lines with TPWS isolated what must happen before permission is given to pass a section signal?

Answer 24

All signals controlled by the next signal box must be set to proceed.