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Train protection and warning system (TPWS)

The train protection and warning system (TPWS) was introduced to comply with the Railway Safety Regulations, 1999 following the Southall and Ladbroke Grove passenger train collisions. It was seen as a stop-gap ahead of the introduction of European Rail Traffic Management System (ERTMS), and was not at the time intended to be a long-term system solution to reduce signals passed at danger (SPADs) and over-speeding risks.

TPWS operates by a combination of train-borne equipment and track mounted sensors. It automatically applies the brakes on a train that has passed a sensor at a speed higher than it should, thus minimising the consequence of a SPAD.

The introduction of TPWS+, that prevents higher speed trains approaching signals and junctions at greater than the permitted speed also serves to reduce overall SPAD and over-speeding risks.

Since the introduction of TPWS in the early 2000s, the risk from SPADs has reduced considerably because the TPWS has reduced the risks from the most hazardous events, although the overall number of SPADs shows a slower reduction. In the last decade the number of highest risk Category A SPADs (with a high ranking of 20 and above) has reduced from 134 in 2001 to less than 17 in 2010. See graph of SPADs by risk ranking score:

Trends in the number of SPADs by risk ranking score 

Source: RSSB

Industry activity

As a result of the current programme for rolling out ERTMS, TPWS is going to remain in operation for a considerable period beyond its original design life (possibly beyond 2046). In recognising this, the industry has developed a long-term strategy to ensure its continuing reliability and availability of parts etc.

The mainline industry, facilitated by RSSB formed a strategy group to look at how TPWS can be maintained on the network until the implementation of ERTMS. As TPWS involves both Network Rail and train operator equipment, it is vital that relevant duty holders collaborate to ensure that TPWS is managed appropriately to ensure that it is safe now and stays safe in the future. In November 2009, RSSB’s Vehicle/Train Control & Communications System Interface Committee (V/TC&C SIC) published a strategy for TPWS.

Their strategy concludes:

For the Train Protection and Warning System (TPWS) to remain an effective train protection system for use on the mainline railway network for the next 30 to 40 years, the strategy will be for the railway industry to cooperate to:

  • Ensure TPWS continues to comply with the requirements of the 1999 Railway Safety Regulations and the relevant exemptions.
  • Ensure TPWS continues to be reliable and continues to meet or exceed the minimum availability requirements specified in Railway Group Standard GE/RT8030.
  • Review the application of TPWS to infrastructure and trains on an on-going basis to ensure that the risk mitigated by TPWS, in conjunction with other risk mitigation measures, remains as low as reasonably practicable.

ORR activity

We believe there is value in train operators introducing improved monitoring that constantly checks the on-board equipment is functioning correctly. Whilst the probability of a collision occurring as a result of defective TPWS equipment is very low, the consequences could well be catastrophic.

Another significant shortcoming of TPWS functionality is the phenomenon of ‘reset and continue’. This can occur when the TPWS deploys the brake, brings the train to a halt, and the driver simply resets the system and continues.

We are seeking evidence that train operators have identified and measured the risk to their operations from TPWS in-service failures and from reset and continue. New versions of the TPWS equipment include features that minimise the likelihood of these events and we believe that train operators should look at occasions such as refurbishment or ERTMS fitment as suitable moments to upgrade their TPWS equipment.

Last updated: October 2012