Ensuring that passengers experience safe, efficient and reliable train journeys has never been more important. With the world’s population and the consequent demand on railway infrastructure increasing, our experts specialise in providing solutions that meet the challenges of tomorrow. Drawing on our global expertise in transport, we work with our partners to provide a safety solution that you can trust.
Our Train Protection and Warning System (TPWS) is designed to reduce the likelihood and consequences of a Signal being Passed At Danger (SPAD), or a train exceeding permissible speed, either at a permanent speed restriction or on the approach to a set of buffer stops.
The system provides the train protection capability of a train stop and an over speed sensor, together with the traditional Automatic Warning System (AWS) functionality of the UK railway. The result is that passengers, and trains, stay safe, secure and on the move.
A heritage of expertise
TPWS has already been keeping passengers safe throughout the UK for the past 15 years. It has also been installed in Australia, in the state of Victoria.
Our experts conceived the concept of TPWS in 1995 and developed it into the trustworthy system that we know today, in order to provide protection across the entire UK rail network, winning multiple awards over the years for innovation and teamwork. Our team based the design on the Correct Side Door Enable system (CSDE) developed for London Underground that ensures that only the correct passenger doors can be opened on London Underground trains.
MK4 Control Unit
The TPWS Mk4 Control Panel is also known as the TPWS Driver-Machine Interface (DMI) and is located in the cab on the driving desk. Compared to the Mk1 (and Mk3) TPWS Control Panel, it features three separate indicators to clearly show the cause of a brake demand: SPAD (Signal Passed At Danger), Overspeed and AWS (Automatic Warning System). It also adds a covered ‘Brake Release’ button to involve the driver in the brake release process – pressing this button together with whichever of the three brake demand indicators/buttons is lit.
e-AWS receiver/e-TPWS receiver
Thales has been proactive in seeking ways to improve the performance of the overall Train Protection systems on UK rolling stock and to this end has developed and certified new products which replace the old, electromechanical AWS components with modern, solid state, highly reliable electronic equivalents.
For new-build vehicle Thales supply an Electronic TPWS receiver (E-TPWS) that combines the AWS receiver function in a single, lightweight unit together with the TPWS aerial and a composite aerial harness.
For retrofit applications where AWS is already fitted, Thales supplies an Electronic AWS receiver (E-AWS), which replaces the existing electromechanical device.
The Overspeed sensor operates on the principle of measuring, on the train, the time taken to pass between two points on the track; if this time is less than a pre-set time (nominally 1 second) a brake demand is activated. On the track two small inductive loops define the points at which the timing starts (Arming loop) and stops (Trigger loop), the Trigger loop being at the required Over speed Sensor location and the Arming loop at some distance in rear; the distance between the loops defines the nominal Over speed Sensor setting. The loops are activated only when the signal is showing the red aspect. The Arming and Trigger loops operate at different frequencies so that trains travelling in the opposite direction do not detect the correct sequence and therefore disregard the sensor.
The Train Stop operates independently of the Over speed Sensor but on a similar principle, using an Arming loop and Trigger loop which are activated only when the signal is showing the red aspect. Train Stop loops, however, are mounted close to the controlling signal and within 10mm of each other such that their fields overlap.
A Brake Demand is made if the Arming frequency is detected followed by both the Arming and Trigger frequencies together, and there is no maximum time limit. This method of detection ensures that there is no minimum speed below which the Train Stop will not operate.
Composite Aerial Harness
The Composite Aerial Harness replaces the two part TPWS Train borne Aerial and Flexible Conduit harness, which are currently fitted to most of the UK rolling stock.
The Composite Aerial is a direct replacement for the existing two-part system, and is available in a variety of lengths, with either a straight or right angle Amphenol connector, or Litton connector. Alternatively the harness can be supplied with terminals, for hard wiring directly to the TPWS Aerial Junction Box.
AWS Acknowledge Pushbutton
This switch is mounted in the driver’s cab and allows the driver to acknowledge AWS warnings before a brake application is demanded by the system.
It is also used to acknowledge brake demands made where the train has passed over an active Train Stop, or exceeded the speed set by an Over speed Sensor.
Trackside aerial loop and feeder cables
The trackside loop aerial is a multi-turn loop 1m in length and 400mm wide constructed from a screened multi-core cable with an integral junction box housing the circuitry.
Each Overspeed Sensor or Train Stop equipment requires a pair of loops. Each loop is mounted on the sleepers between the running rails and fed from the Trackside Equipment via a screened twisted pair feeder cable.
Trackside Overspeed sensor units
An Overspeed Sensor Unit (case coloured yellow for Normal Direction and blue for Wrong Direction) is required for each pair of Overspeed sensor loop aerials.
It has four externally visible LED’s as follows:
A green LED indicating that power is present.
A yellow LED indicating that the MAIN I/P/MAIN SIG. (red aspect) is required to be lit (‘ON’).
A yellow LED indicating that the SUPP I/P/SUB. SIG. (clear aspect) is ‘ON’.
A red LED indicating a fault (this indication is latched until power is switched off).
Temporary isolation switch/panel
Temporary Isolation is used in various operating circumstances where it is necessary for the Train Stop and Overspeed Sensor to be disabled temporarily on the train, such as propelling, tandem operation or ticket working. Whilst Temporarily Isolated the train borne equipment does not respond to Overspeed Sensors or Train Stops. Activation of the Temporary Isolation switch during an existing brake demand does not cancel the brake demand.
Trackside power supply modules
A standard Power Supply & Signalling Interface Unit (case coloured red) is required for each Train Stop and Overspeed Sensor Unit and is located adjacent to its associated unit. There is also a dc supply option available, the Power Supply & Signalling Interface 24Vdc unit (case coloured white).
Alarm & Indicator Unit
This is the standard type that has been in use for a number of years for AWS visual and audible indications. It comprises a rectangular housing, which incorporates a three-inch diameter AWS Indicator (Sunflower) that may display either an all-black circle or a circle comprising alternate black and yellow segments.
Three types of cabinet are available which contain either one or two sets of trackside equipment, or individual TPWS function (either a Train Stop or Over speed sensor).
Each Set is associated with one signal and where it exists its subsidiary signal and provides one Overspeed Sensor and one Train Stop facility.
The Control Panel provides indication to the driver as to the status of the train borne equipment, both in normal operation and failure modes. It comprises a rectangular plate on which is mounted two indicators and a switch/indicator.
The Control Unit performs all the logic functions of AWS, Overspeed Sensor and Train Stop, taking inputs from the AWS Receiver and the TPWS Train borne Aerial and providing a direct output to the brake control circuit, which operates the emergency brake, and an output to reset the AWS Receiver via the Acknowledge Button.