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Train Protection & Warning System
The Train Protection & Warning System (TPWS) is a train protection system used throughout the British passenger main-line railway network, and in Victoria, Australia.
According to the UK Rail Safety and Standards Board, 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: passed a signal at danger without authority; approached a signal at danger too fast; approached a reduction in permissible speed too fast; approached buffer stops too fast. TPWS is not designed to prevent signals passed at danger (SPADs) but to mitigate the consequences of a SPAD, by preventing a train that has had a SPAD from reaching a conflict point after the signal.
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 train stops which accomplish a similar task using electro-mechanical technology. Buffer stop protection using train stops is known as ‘Moorgate protection' or 'Moorgate control’.
TPWS was developed by British Rail and its successor Railtrack, following a determination in 1994 that British Rail's Automatic Train Protection system was not economical, costing £600,000,000 equivalent to £979,431,929 in 2019 to implement, compared to value in lives saved: £3-£4 million (4,897,160 - 6,529,546 in 2019), per life saved, which was estimated to be 2.9 per year.
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 introduction of ATP and ERTMS, nothing should impede the installation of the much more capable European Train Control System.
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Train Protection & Warning System
The Train Protection & Warning System (TPWS) is a train protection system used throughout the British passenger main-line railway network, and in Victoria, Australia.
According to the UK Rail Safety and Standards Board, 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: passed a signal at danger without authority; approached a signal at danger too fast; approached a reduction in permissible speed too fast; approached buffer stops too fast. TPWS is not designed to prevent signals passed at danger (SPADs) but to mitigate the consequences of a SPAD, by preventing a train that has had a SPAD from reaching a conflict point after the signal.
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 train stops which accomplish a similar task using electro-mechanical technology. Buffer stop protection using train stops is known as ‘Moorgate protection' or 'Moorgate control’.
TPWS was developed by British Rail and its successor Railtrack, following a determination in 1994 that British Rail's Automatic Train Protection system was not economical, costing £600,000,000 equivalent to £979,431,929 in 2019 to implement, compared to value in lives saved: £3-£4 million (4,897,160 - 6,529,546 in 2019), per life saved, which was estimated to be 2.9 per year.
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 introduction of ATP and ERTMS, nothing should impede the installation of the much more capable European Train Control System.