TPWS Flashcards
What is the purpose of the Train Protection and Warning System (TPWS)?
The purpose of TPWS is to stop the train by automatically initiating a brake demand, where TPWS track equipment is fitted, if the train has:
1. Passed a signal at danger
2. Approached a signal at danger too fast
3. Approached a reduction in permissible speed too fast
4. Approached buffer stops too fast
What does TPWS mitigate against?
TPWS is not designed to prevent SPADs but to mitigate against the consequences of a SPAD, by preventing a train that has had a SPAD from reaching a conflict point ahead of the signal.
Does TPWS relieve the driver of responsibility?
No, TPWS does not relieve the driver of the responsibility for observing signals and speed restrictions.
Where is TPWS provided on passenger lines?
TPWS is provided at all main running signals capable of displaying a stop aspect which protect crossings or converging movements.
Where is TPWS provided on non-passenger lines?
TPWS is provided at any signal capable of showing a stop aspect on a non-passenger line, where that signal protects a crossing or convergence with a passenger line.
Where is TPWS fitted on the approach to buffer stops?
TPWS is fitted on the approach to buffer stops at the end of passenger platforms, approximately 65 metres from the buffer, and will trigger a brake application at speeds greater than 10mph.
When is TPWS activated on the approach to permissible speed reductions?
TPWS is activated on the approach to permissible speed reductions, where the permissible speed on the approach is 60mph or more and the reduction in the permissible speed is at least one third.
What does TPWS track equipment consist of?
TPWS track equipment consists of a train stop system (TSS) and overspeed sensor system (OSS).
Where is the TSS mounted?
The TSS is mounted in the four foot at the associated signal.
When is the TSS energised?
The TSS is energised when the signal is at danger.
What does an OSS comprise?
An OSS comprises two transmitters: arming loop and a trigger loop.
What happens when a train passes over an arming loop?
When a train passes over an arming loop, the on-train equipment detects it and starts an internal timer.
What occurs if a train passes over a trigger loop within a designated time?
If the train passes over a trigger loop within a designated time, indicating that the train is exceeding a set speed, then the on-train TPWS equipment will initiate a brake demand.
When are OSS loops energised on the approach to stop signals?
OSS loops on the approach to stop signals are only energised when the signal is at danger.
When are OSS loops energised on the approach to speed reductions or buffer stops?
OSS loops on the approach to speed reductions or buffer stops are permanently energised.
What signals are fitted with TPWS?
Signals fitted with TPWS have a TSS and may also have an OSS.
Can some signals have more than one OSS?
Yes, some signals have more than one OSS.
What equipment is provided on each fitted traction?
The following equipment is provided:
• TPWS receiver
• TPWS control panel
• AWS/TPWS acknowledgment button
• TPWS temporary isolation switch
• AWS/TPWS full isolation switch
Where is the TPWS receiver located?
The TPWS receiver is located at the front of the train.
What does the TPWS receiver do?
It senses the train’s passage over TPWS loops and sends this information to the control unit.
What is found in the driving cab of the train?
The TPWS control panel, which has two indicators and one illuminated button.
What does the red brake demand indicator indicate when it is off?
No brake demand has been initiated.
What does the red brake demand indicator indicate when it is flashing?
TPWS or AWS has initiated a brake demand that has yet to be acknowledged by the driver.
What does the red brake demand indicator indicate when it is on (steady)?
The brake demand has been acknowledged by the driver.
What does the yellow temporary isolation/fault indicator indicate when it is off?
TPWS state is normal.
What does the yellow temporary isolation/fault indicator indicate when it is flashing?
A fault has been detected in the train TPWS equipment, or the start-up test has not been completed successfully.
What does the yellow temporary isolation/fault indicator indicate when it is on (steady)?
The train TPWS equipment has been temporarily isolated.
What does the on-train TPWS do when the driving cab is opened?
The on-train TPWS carries out a self-test to check that the equipment is functioning correctly. When this test starts, all three indicators illuminate.
What happens if the TPWS self-test is completed successfully?
If the test is completed successfully, the indicators extinguish.
What does it mean if the Temporary Isolation light flashes?
The Temporary Isolation light flashes if a fault is detected or if the receiver is over an active grid.
What is the purpose of the Train Stop override button?
The yellow button is used to override the brake demand from the TSS loop for approximately 20 seconds or 60 seconds for slower freight.
What happens when the Train Stop override button is pressed?
Once pressed, the Train Stop override button will illuminate and extinguish when the train passes over the TSS.
What must you do if you have a TPWS brake demand?
You must press the AWS/TPWS acknowledgment button.
What happens after pressing the acknowledgment button for a TPWS brake demand?
The brakes will release, and the indicator will clear 60 seconds after the brake demand was initiated.
What is the TPWS temporary isolation switch?
The TPWS temporary isolation switch is generally mounted in the driver’s cab but out of reach of the normal driving position.
What is the purpose of the TPWS temporary isolation switch?
It allows the driver to perform certain operational movements that would otherwise cause an unsolicited brake demand.
When should the TPWS temporary isolation switch be operated?
You can find when to operate the switch in the rule book.
Does temporarily isolating the TPWS affect AWS?
No, temporarily isolating the TPWS does not affect AWS.
What are AWS/TPWS full isolation switches?
Traction units are fitted with AWS and TPWS full isolation switches, which may be separate or combined.
Can the AWS/TPWS full isolation switches be reached from the driving position?
No, they cannot be reached from the driving position.
When might it be necessary to operate the AWS/TPWS full isolation switch?
It may be necessary to operate the switch where there is a fault with the AWS system.
What happens if a train stops directly over an AWS magnet?
The driver will not be able to cancel the AWS.
What should a driver do if no other option is available after stopping over an AWS magnet?
It may be necessary for the driver to operate the full isolation switch.
What happens if the driver isolates the AWS in cabs fitted with the standard TPWS control panel?
The TPWS will be isolated automatically.
What must you not allow when starting a journey from a maintenance depot?
You must not allow a train to start a journey if the TPWS is not working in any cab which is required to be driven from when TPWS is required to be in operation.
What can you allow when starting a journey from somewhere other than a maintenance depot?
You can allow a train to start a journey with the TPWS defective in the cab to be driven from, if TPWS will not be required to be in operation during the journey.
You must tell control at the first convenience and carry out any instructions given.
What can you do if TPWS is defective in the cab to be driven from when not carrying passengers?
You can allow a train to start a journey to travel to a maintenance depot for repair if you tell the signaller and get permission for the train to start a journey in this condition.
What must you do if the TPWS becomes defective during a journey when it should be in operation?
You must stop your train immediately, tell the signaller, not move the train until instructed to do so, and carry out the instructions given.
What must you do if the TPWS becomes defective during a journey when it is not required to be in operation?
You must tell control at the first convenient opportunity and carry out any instructions given.
What should you do if TPWS has failed to activate?
Stop your train immediately, tell the signaller, not move the train until instructed, and carry out the instructions given.
What to do if TPWS is defective and permission is given to start a journey?
Follow the conditions in the table during any part of the journey where TPWS would normally be in operation.
What is the speed limit for freight trains and OTMs if a competent person is not provided?
Freight trains and OTMs can proceed at a speed not exceeding 50mph.
What is the speed limit for all other trains if a competent person is not provided?
All other trains can proceed at no more than 60mph until a competent person is provided.
What is the speed limit for trains if a competent person is provided?
Proceed at normal permissible speed.
