Train protection

Train protection is equipment fitted to trains and the track that can reduce risks from signals passed at danger (SPADs) and over-speeding. 

Train Protection Warning System (TPWS) is the most widely used train protection system in Britain although on some routes Automatic Train Protection (ATP) is used. 

London Underground has incorporated a train protection system for many years, originally in the form of mechanical train stops but increasingly these are being replaced by electronic forms of ATP equipment. 

The European Rail Traffic Management System (ERTMS) will replace TPWS and ATP in the future.


Over the years there have been a number of serious incidents following SPADs, including collisions at Southall and Ladbroke Grove where lives were lost. In 1999 the Railway Safety Regulations (RSR 99) introduced a requirement to introduce a train protection system. 

TPWS was installed across the network by the end of 2002 and is successfully reducing SPAD risk as there have been a number of recorded incidents where TPWS has intervened to avoid a potential collision.  In some places TPWS+ (which is effective at higher operating speeds than TPWS) has been installed. 

On certain routes ATP is used and this system continuously monitors train speed to ensure that the train is at the right speed for that railway. TPWS is seen as a stop-gap ahead of the introduction of European Rail Traffic Management System (ERTMS), and was not intended to be a long-term system solution to reduce signals passed at danger (SPADs) and over-speeding risks.

Train protection systems on other rail systems

The installation of train protection systems should be considered for all forms of rail transport systems. Metro systems such as the London Underground require robust systems that can minimise the consequence of a signal, or end of movement authority, being passed in error. 

Other rail systems such as trams and heritage railways may be able to demonstrate that such technology is not required. The justification is likely to be based on the number and speed of vehicles or the ability to stop within line of sight of obstructions.

Train protection systems and the European Rail Traffic Management System

In line with European directives, the national network is now committed to a migration plan that will replace TPWS with ERTMS which will provide a higher level of train protection whilst helping the railway towards a more cost efficient signalling system.

However the programme for rolling out ERTMS across the network will take some time and 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 to achieve the aim of continued safe operation of TPWS.

Safety performance and monitoring

We publish quarterly reports on the numbers of SPADs which includes a summary of the key trends:

We expect that train operators will identify the risk to their operations from TPWS in-service failures and from 'reset and continue' (this may occur when the TPWS deploys the brake, brings the train to a halt, and the driver simply resets the system and continues) and take appropriate actions to mitigate them. 

New versions of the TPWS equipment include features that minimise the likelihood of these events and we believe that train operators should take suitable opportunities (such as refurbishment programmes) to upgrade their TPWS equipment where appropriate.