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.
