Train Protection & Warning System

The Train Protection & Warning System (TPWS) is a train protection system throughout the two UK passenger main-line railway networks, and in Victoria, Australia.

The UK Rail Safety and Standards Board's definition is:

The purpose of TPWS is to stop a train by automatically initiating a brake demand, where TPWS track equipment is fitted, if the train has:

A standard installation consists of an on-track transmitter adjacent to a signal, activated when the signal is at danger. A train that passes the signal will have its emergency brake activated. If the train is travelling at speed, this may be too late to stop it before the point of collision, therefore a second transmitter may be placed on the approach to the signal that applies the brakes on trains going too quickly to stop at the signal, positioned to stop trains approaching at up to 75 mph (120 km/h).

At around 400 high-risk locations, TPWS+ is installed with a third transmitter further in rear of the signal increasing the effectiveness to 100 mph (160 km/h). When installed in conjunction with signal controls such as 'double blocking' (i.e. two red signal aspects in succession), TPWS can be fully effective at any realistic speed.

TPWS is not the same as timed train stops that accomplish a similar task with different technology.

TPWS was developed by British Rail, later Railtrack, working group as a development of the Automatic Warning System, after a 1994 decision that the nationwide installation of a full Automatic Train Protection system was not practicable. Trial installations of track side and train mounted equipment were made in 1997, with trials and development continuing over the next two years.

The rollout of TPWS accelerated when the Railway Safety Regulations 1999 came into force in 2003, requiring the installation of train stops at a number of types of location. However, in March 2001 the 'Joint Inquiry Into Train Protection Systems' report found that TPWS had a number of limitations, and that while it provided a relatively cheap stop-gap prior to the widescale installation of ATP and ERTMS, nothing should impede the fitment of the much more capable European Train Control System.

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