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The European Rail Traffic Management System (ERTMS) is a signalling and traffic management system developed with the backing of the European Union. The objective of ERTMS, mandated by European law on designated routes, is to allow seamless operation ("interoperability") across international borders without the problem of having incompatible signalling systems on either side. It also has the potential to improve line capacity and reduce installation costs. The train control (signalling) element of ERTMS is called the European Train Control System (ETCS).

ETCS transmits a 'movement authority' to the train, specifying the distance that it is permitted to travel and data about the track ahead, such as speed restrictions and gradients. A computer on board the train uses this information together with data concerning the train, such as its braking capability, to calculate the permitted speed as well as a safe braking profile approaching the end of authority (EOA). An on-board odometry system keeps track of the train's position, allowing the system to check that the movement authority is not exceeded. ETCS can provide cab signalling, with or without the provision of lineside signals for non-fitted trains. Since the permitted speed is continuously displayed inside the cab, railways that operate exclusively with cab signalling are not provided with lineside speed restriction signs, except where required for degraded operation. Temporary speed restrictions can be programmed into the system, so that they are supervised in the same way as permanent speed restrictions. Speed information is expressed in kilometres per hour.

ETCS Levels

There are three distinct levels of ETCS, as defined by the manner in which movement authorities are transmitted to trains and the means by which the trains' positions are reported to the control centre.

Fig. 1: A Eurobalise on an ETCS Level 2 fitted line.

ETCS Level 1 provides Automatic Train Protection (ATP) functionality overlaid onto conventional lineside signalling with continuous train detection. Infrastructure data is stored in 'lineside electronic units' (LEUs) which are distributed along the lineside. Movement authorities are transmitted to passing trains by transponders, known as 'balises', mounted in the 'four-foot'. ETCS Level 1 uses controlled balises, capable of transmitting variable data according to signal aspect. They receive their information via the LEUs. Trains not fitted with ETCS train-borne equipment can continue to operate in accordance with the lineside signals and under the protection of AWS and TPWS. This is also the fall-back mode of operation if ETCS should fail. Level 1 delivers interoperability and improves safety, but the intermittent nature of the ATP supervision leads to a small reduction in line capacity.

ETCS Level 2 continuously transmits movement authorities to the train via a GSM-R radio network. The infrastructure data is held centrally at the control centre. Balises are installed only as position markers, transmitting fixed data to initialise and occasionally recalibrate the train's odometer. Continuous train detection is provided by track circuits or axle counters. Although ETCS Level 2 is designed as a standalone cab signalling system, it can be overlaid onto conventional lineside signalling so that trains not fitted with ETCS train-borne equipment may still run on the line.

ETCS Level 3 does not require continuous train detection. The train determines its position from fixed balises (as per Level 2) and reports this information to the control centre via GSM-R radio. The control centre determines track section occupancy from position reports received from trains and continuously transmits movement authorities to trains via the GSM-R. Since the train continuously monitors its own position, Level 3 can support moving block operation, which provides the best possible line capacity. In the absence of conventional train detection, the train-borne equipment must continually check that the train is complete. Only trains fitted with ETCS train-borne equipment can run on a Level 3 fitted railway.

Level 0 refers to the operation of an ETCS-fitted train over a non-fitted line, with minimum supervision (see 'unfitted' mode in table 1 below).

Driver-Machine Interface (DMI)

Vital information relating to the safe control of the train is displayed on the 'driver-machine interface' (DMI) inside the active driving cab. The DMI displays the distance to the EOA and the train's actual speed, as well as the permitted speed and target speed. The colour of the speedometer display changes from white to yellow if a reduction in permitted speed is necessary. If the driver fails to reduce speed as required, the display changes to orange and a warning horn sounds. If speed has still not been reduced, the display turns red and a full service brake application is automatically initiated.

The table below gives details of the various operating modes. Where appropriate, a symbol displayed on the DMI indicates the mode that is currently selected.

Symbol Mode Description
Full supervision (FS) This is the normal non-permissive movement authority, giving full protection. The train is permitted to run at the maximum speed shown.
On sight (OS) This movement authority allows the train to enter an occupied section of line. The train must proceed at such a speed that it can stop short of any obstruction. The speed is supervised up to a ceiling speed. On sight mode can be received while the train is in motion.
Shunt (SH) This mode is used during shunting. The train's speed is supervised up to a ceiling speed. Display of the Shunt symbol is not an authority to move the train.
Non-leading (NL) This mode is selected on the rear traction unit when running in tandem or banking, etc. It provides limited supervision.
Staff responsible (SR) This mode allows the train to be moved under the driver's own authority on an ETCS equipped line. The train's speed is supervised up to a ceiling speed.
Standby (SB) This is the default mode, automatically selected when opening or shutting down the driver's desk.
Unfitted (UN) This mode is selected when driving on lines not fitted with ETCS. The DMI will display no information other than the train's speed, in miles per hour, which is supervised up to a ceiling speed.
Trip (TR) This mode is automatically selected in the event of a movement authority being exceeded, until acknowledged by the driver. An emergency brake demand will occur.
Post trip (PT) This mode follows an emergency brake demand, once the driver has acknowledged the trip and the train has come to a stand.
- Sleeping (SL) Where a locomotive or unit has more than one set of ETCS equipment, only one set can be active at any time. The other sets will be in Sleeping mode.
System failure (SF) This mode is associated with failure of the ETCS system and is accompanied by an emergency brake demand.
- No power (NP) This mode is entered when no power is applied to the ETCS system. It is accompanied by an emergency brake demand.
- Isolation (IS) This mode applies when the driver has isolated the ETCS following a system failure.
Table 1: ETCS Operating Modes.

If the DMI display goes blank because of equipment failure, the train will automatically be braked to a stand.

ETCS on the Cambrian Lines

ETCS Level 2 cab signalling was provided on the Cambrian Lines in 2010/2011, replacing the life-expired RETB infrastructure. This 'early deployment scheme' (EDS) was the first use of ETCS in Britain.

The ETCS signalling centre for the Cambrian Lines is situated at Machynlleth. Signalmen set routes using VDU display systems in a similar manner to conventional signalling. The limits of a route are defined by 'route setting positions' (RSPs) rather than signals. RSPs, like signals, can be either 'controlled' or 'automatic'. A controlled RSP is always indicated at the lineside by a block marker, whereas there may be no physical lineside marker in the case of an automatic RSP.

As with conventional Track Circuit Block signalling, overlaps are provided in advance of the block markers. In some cases, the signalman can select either a 'normal' or 'extended' overlap, as appropriate for the type of train. The length of the overlap determines the 'release speed'. The ATP function will only supervise the train's speed until it has been reduced to below the release speed, so allowing the train to draw right up to the block marker. Selection of the wrong overlap does not compromise safety.

Figure 2 shows an example of a typical crossing loop.

Figure 2
Fig. 2: ETCS Level 2 Crossing Loop Layout.

Continuous train detection by axle counters is provided on all running lines. The points are controlled by conventional power operation. Block markers are provided at controlled RSPs. There are no distant boards, and neither AWS nor TPWS is provided. Shunt entry boards are installed as necessary to accommodate shunting movements. For example, the shunt entry boards shown in figure 2 facilitate shunting from one loop to the other, e.g. when running round a train. The block markers on the single line allow another train to approach while this is taking place. Balises are fitted at every block marker and shunt entry board and at other locations as required.