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Main Line ATO Becomes a Reality

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Much publicity has been given to the recent running of the first passenger train across the Thameslink central core in London using ETCS Level 2 with Automatic Train Operation (ATO) superimposed on to it.

Rightly considered as a significant event in the development of rail signalling, a search for a deeper explanation as to what is involved resulted in Rail Engineer being invited, along with the IRSE International Technical Committee, to see how the system was developed and to ride through in the cab so as to witness the ATO performance in real terms.

Map showing part of the 'Thameslink' route in 1914.
Map showing part of the ‘Thameslink’ route in 1914.

Early days

It is easy to think that Thameslink is a new north-south rail link across the capital in the same way that Crossrail (Elizabeth line) is for the east-west connection. This is far from true, since the Thameslink route was provided in Victorian times and had a passenger service up until the First World War.

Never a commercial success, mainly because its extremities were controlled by different railway companies, which did not have the vision for operating through trains, the route soldiered on as a cross-London freight artery until the 1970s.

When this ceased, the line closed and the track was lifted on the short section from Farringdon to Holborn Viaduct, leaving only the spur line to Moorgate with a peak hour passenger service from the Midland main line at St Pancras. Luckily the track bed remained undeveloped.

With the coming of the British Rail business sectors, and the creation of Network South East, the erstwhile BR Regional mentality was swept aside and the potential for a north-south link became apparent. With track relaid and signalling installed at minimum cost, the route reopened in the late 1980s and became an instant success.

However, with the difficult linkage at the southern end, primarily getting paths through London Bridge and the continuing commitment to provide services to Moorgate and Holborn Viaduct, capacity constraints were evident from day one. Something had to be done to provide even a half decent service.

Closure of Holborn Viaduct station, being replaced by the new City Thameslink station, which entailed putting the line underground south of Blackfriars and removing the overbridge on Ludgate Hill, improving the view of St Pauls Cathedral in the process, was a first step and enabled 15 eight-car trains per hour (tph) to be run in each direction.

These changes helped, but the line was never going to be capable of coping with the traffic potential. More drastic solutions were needed.

The Thameslink programme

Key elements were identified as necessary if Thameslink was ever going to be the railway that mirrored what Paris had achieved with the creation of the RER network. These were:

  • Lengthening platforms to accommodate 12-car trains;
  • Closure of the Moorgate spur and train service in 2009 to permit platform lengthening at Farringdon, also enabling additional trains to be run through the entire central core;
  • Sorting out the conflicting paths at the south end of Blackfriars station;
  • Remodelling the approaches to London Bridge station to eliminate as far as possible all flat junctions for Thameslink trains;
  • Provision of a new station at Kings Cross/St Pancras to cope with both domestic and international travellers;
  • Connecting the Thameslink route to the East Coast Main Line via the new Canal Tunnels;
  • Provide a signalling system that could cope with the 24 trains per hour (tph) goal.

An increase in capacity to 16tph was achieved by December 2011, and all but the last of the above elements have now been completed. Many articles reporting progress on these have appeared regularly in Rail Engineer, the completion of the huge London Bridge project being a major feature in issue 160 (February 2018).

In parallel, the challenge of providing ATO on main line railways was examined in issue 150 (April 2017). This is associated with the last point above and is the focus of this article.

Why ETCS and ATO?

Thameslink has a modern but conventional signalling system, so why is this not good enough?

Extensive analysis and modelling revealed that, to achieve the intended 24 tph, optimised braking and acceleration rates would be required with trains closing up to the shortest possible separation. Only with ATO can this be achieved, but this requires a signalling system that can support it.

A metro solution using CBTC (communications-based train control) would be possible, but Thameslink connects to main line railways including the ECML where ETCS is the intended solution for the signalling of that line. As such, it made no sense to equip the Thameslink fleet with two separate systems, one of which would only be in use for the short four-mile central core section. Thus, ETCS was the only real choice, but with the need to develop the ATO package superimposed upon it.

Much has been written about ETCS Level 2 within the overall ERTMS package. This provides a well-proven ATP (Automatic Train Protection) SIL4 (safety integrity level 4) system giving speed and ‘distance to go’ Movement Authority (MA) information to the driver by means of the GSM-R track-to-train radio link.

The ATO element is primarily to interpret the ETCS commands and interface these to the train traction and braking systems. Enhancement of the normal ETCS infrastructure is fairly minimal but does require additional balise groups to achieve the necessary accuracy to stop trains at the right station platform position. With safety being assured by the ATP system, ATO has only to be designed to a SIL2 category and the package has been adapted from metro ATO equipment used elsewhere.

The development has been a 10-year joint exercise between Network Rail, Siemens, supplier of both the Class 700 train fleet and the signalling system, and Govia Thameslink Railway (GTR), which developed the operational concept and will run the train service as well as take ultimate responsibility for the train-borne equipment. Network Rail is the system integrator on behalf of the Department for Transport.

An initial modelling of the core route from just north of St Pancras International to Blackfriars led to a system integration laboratory being set up with all the infrastructure and train-borne elements present to allow integration testing. Equipment used is mainly standard component parts proven in service elsewhere and includes:

  • A Westlock solid state interlocking;
  • A Radio Block Centre (RBC), as commonly used on ETCS projects;
  • A European Vital Computer (EVC), which is the intelligence on the train;
  • A dynamically programmable track balise to represent balises encountered on the simulated route sections;
  • An underfloor train antenna to read the track balises;
  • Three GSM-R base stations to provide a reference radio network;
  • Simulated train odometers to measure distance travelled with a speed probe unit to simulate wheels going round;
  • A Doppler radar to measure speed independent of wheel rotation and transmitters to simulate movement;
  • A Class 700 cab complete with ETCS DMI (driver-machine interface – the visual display), ATO indication and GSM-R radio.

This provides a simulation of the system performance with the ability to ‘drive’ trains through the core section using video images of the track layouts and routes. These test the interaction and integration between trackside and train-borne components in given operational scenarios.

Having designed and proven the system in laboratory conditions, a trial system was then set up at the ETCS National Integration Facility (ENIF) on the Hertford Loop using the Class 313 ERTMS test train, this taking place from 2015 onwards.

Also, in 2015, and once the whole ETCS concept had been verified, an important next stage was the transfer of control for the whole central core section onto new ETCS-capable work stations at Three Bridges ROC (Railway Operating Centre), as having a single control centre would be one less complication. This enabled initial testing of both ETCS and ATO to take place overnight on the central core using a Class 700 train.

In December 2017, the Canal Tunnel link, from St Pancras to the ECML just north of King’s Cross, was brought into use, thus completing all the routes that would make up the extended Thameslink service.

Enhancements to the GSM-R infrastructure have been made to give improved resilience in case of a base-station failure. Some problems with radio interference have been noticed, which are being investigated and potential solutions sought.

The 115-strong Class 700 train fleet all came fitted with ETCS and ATO equipment, with two units being used specifically for integration testing. This has allowed further ETCS and ATO testing to take place through the central core.

Although Siemens is the supplier of both ETCS infrastructure and train-borne equipment, the two come from different generations of design. The RBC emanates from the Invensys product, developed originally in Spain, and is at software version 2.3.0d, whereas the train kit comes from the Siemens Berlin factory and is at version 3.3.0 software, thus meeting the interoperability requirements. It is recognised that once the ECML ETCS goes live, both ETCS infrastructure and train borne equipment may require upgrading to whatever the latest software version is at the time.

The GSM-R radio infrastructure comes from Kapsch, with the train and cab radios being supplied by the Siemens facility in Poole, Dorset. For the present, the GSM-R connection between ground and train is circuit switched meaning a continuous connection between the control centre and the train once log-in has occurred. Again, the move to the packet switching GPRS standard may need to happen once the East Coast line ETCS goes live in order to ensure sufficient capacity within the GSM-R bandwidth allocation.

ATO operation

The Class 700 trains can operate in four possible modes:

  • Level 0, meaning no supervision with both ETCS and TPWS/AWS isolated – to be used only in an emergency situation should failures occur;
  • Level NTC (National Train Control), which is the normal UK standard for train operation employing both TPWS and AWS plus lineside signals;
  • Level 2, using ETCS for a line equipped with an RBC, Eurobalises and GSM-R radio;
  • ATO for trains equipped with both ETCS Level 2 and ATO equipment.

Another feature, known as L2 Inhibit, will allow trains to be driven in the ETCS area in NTC mode, using lineside signals and TPWS/AWS, for drivers not trained on ETCS operation.

ATO operation can itself exist in three classifications:

  • Standalone – acceleration and speed are maximised and station dwell time is minimised;
  • Timetable-based – the ATO drives to the timetable;
  • Trackside-driven – the ATO receives updated trip time and dwell time commands as the train journey progresses.

The Thameslink central core ETCS operation commences just south of Kentish Town on the Midland line, at the entrance to the Canal Tunnel on the ECML through to Elephant & Castle on the line down to Herne Hill and to just east of London Bridge Thameslink platforms.

At the start of ETCS capability, the train passes over a four-balise group that triggers GSM-R registration and session management to establish secure communication between the RBC and the train EVC equipment. The train identity is established with the location to allow transmission of the initial MA. Drivers have to acknowledge Level 2 supervision after which they will drive the train to the limits of the MA. If the driver fails to acknowledge ETCS L2, the train will stop.

Once in ETCS L2 full-supervision mode, ATO operation can commence, this being offered by a flashing yellow button on the driver’s console that, when pressed, starts the ATO mode with the yellow light on continuously. The train then proceeds ‘hands off’ and will continue until the next station stop with the acceleration, speed and braking controlled by the train equipment in accordance with the ETCS MA. A double set of balises and the train odometry equipment will ensure a stopping accuracy of ±0.5 metres.

When the train has stopped at the station, the ATO drops out and the doors are released automatically. With station duties completed, the driver closes the doors and re-presses the ATO yellow button, whence the train will move off and proceed to the next scheduled stopping point.

At full operational capacity, it is likely that a train following closely behind the preceding one will be stopped at a signal or ETCS block marker before the station stop. If this happens, the ATO remains active and the train will move again once the MA is extended.

It must be emphasised that the core section has (and will continue to have) lineside signals. Both the MAs associated with ETCS and ATO operation are commensurate with these signals and the system does not permit trains in ATO mode to pass a red signal. An MA will not be given from the RBC until the signal aspect changes. This is to avoid driver unease and contrasts with some systems on the European mainland where ETCS operation can allow red signals to be passed in order to get capacity benefits.

As part of the learning curve, ATO is not mandatory and it is perfectly possible for trains to transit the central core by manual driving to ETCS MA limits. It is likely that, on Sundays and late evenings when the traffic density is lower, drivers will use this method to keep abreast of ETCS operation. In the daytime, and especially peak hours, drivers will be expected to use ATO.

Another decision taken to optimise familiarity is the process of accepting ETCS supervision before commencing ATO – both could happen simultaneously but introducing them sequentially is judged a safer option. The driver can disengage ATO at any time by pressing the ATO yellow button, moving the Power Brake Controller (PBC) or pressing the emergency stop button.

Driving ATO

From the cab ride, ATO appears little different to manual driving, but all movements are optimised. The acceleration rate is identical to normal driving and the braking rate is only 80 per cent of the full service brake application. The ATO is underpinned by an electronic representation of the infrastructure known as the track data base (TDB). This information will need to be updated to take account of any permanent way alterations or changes to the route’s speed profile and will eventually be downloaded to the entire fleet via an ATO server.

Adhesion issues are duly considered and low adhesion conditions can be implemented – the Class 700 trains have automatic sanders, which were witnessed in operation when accelerating from Blackfriars. The core section contains some steep gradients in the City Thameslink station area.

Currently, eight drivers are fully trained in ATO and they, in turn, are training the driver managers. When complete, all of the drivers employed by GTR will be trained, this consisting of one day in a classroom, one day on a simulator and then out on a test train with an instructor alongside.

The training simulators are located at Hornsey and Three Bridges, the main depots for the Class 700 fleet.

Traffic Management

To ensure the best possible train regulation and adherence to the working timetable, in parallel with ETCS and ATO provision, a Traffic Management System is being supplied by Hitachi and will cover the majority of the future Thameslink routes. The timetable will be downloaded into the TMS at the start of each day, whereupon the TMS constantly reviews train movements against the timetable with the intended ability to transmit revised trip and dwell times out to each train before entering the central core ATO area.

TMS will detect timetable conflicts and late running to then offer the optimum pathing plan to the signallers so that potential disruption is kept to a minimum. Once a new or revised train plan is agreed, the routes can be set either by the signaller or automatically, with the TMS interfaced with the ETCS/ATO. The latter will require the integrity of the data to be guaranteed before being contemplated.

So far, timetable data for a few days ahead has been compiled from Luton to Crystal Palace and is being tested within the TMS for conflicts and errors. TMS will become a subject for further articles in due course.

Approaching Blackfriars on the ATO test train.
Approaching Blackfriars on the ATO test train.

Proud to be first

The Thameslink ATO project is not going to solve the challenge of providing ATO on main line railways, since it has only a single type of train (the Class 700) with all trains having the same stopping pattern through the central core. It does, however, give a useful insight into the application of ATO on the main line and the interfaces needed between conventional signalling and ETCS/ATO operation.

ATO will permit 24tph operation when the final Thameslink timetable becomes live in late 2019. From May 2018, an enhanced Thameslink timetable of 18tph will be implemented, giving new route destinations.

Driver training for ETCS and ATO will start this year with routine ETCS and ATO usage beginning in early 2019. Eyes from across the world will be watching to see how effective the ATO will be. The project is a UK-first, and one to be proud of.

Thanks to David Thomas, Philip Powley, Jim Doughty and David Harris from the Thameslink Programme team and to Scott Wilson and Selina Clarke from Network Rail for explaining the technical features and enabling the visit to take place.

Read more: Getting electrification right


Clive Kessell
Clive Kessellhttp://therailengineer.com
SPECIALIST AREAS Signalling and telecommunications, traffic management, digital railway Clive Kessell joined British Rail as an Engineering Student in 1961 and graduated via a thin sandwich course in Electrical Engineering from City University, London. He has been involved in railway telecommunications and signalling for his whole working life. He made telecommunications his primary expertise and became responsible for the roll out of Cab Secure Radio and the National Radio Network during the 1970s. He became Telecommunications Engineer for the Southern Region in 1979 and for all of BR in 1984. Appointed Director, Engineering of BR Telecommunications in 1990, Clive moved to Racal in 1995 with privatisation and became Director, Engineering Services for Racal Fieldforce in 1999. He left mainstream employment in 2001 but still offers consultancy services to the rail industry through Centuria Comrail Ltd. Clive has also been heavily involved with various railway industry bodies. He was President of the Institution of Railway Signal Engineers (IRSE) in 1999/2000 and Chairman of the Railway Engineers Forum (REF) from 2003 to 2007. He continues as a member of the IRSE International Technical Committee and is also a Liveryman of the Worshipful Company of Information Technologists. A chartered engineer, Clive has presented many technical papers over the past 30 years and his wide experience has allowed him to write on a wide range of topics for Rail Engineer since 2007.


  1. Good to see Thameslink adding to it’s list of “Firsts”
    * First Driver Only Operation
    * First operational Cab Radio system
    * First AC/DC Dual traction stock (I think)
    & now First ATO in an ETCS environment

    With a bit of effort and luck they may get the First ETCS L2 packet switched system!

    • Unfortunately Thameslink was not the first service to receive AC/DC Dual Traction stock, the first was the Class 313 running on the Northern City Line

  2. Thanks James.
    You are correct and I should have remembered that as I was on the ER when it all happened. Just that it was further back in the memory banks.

  3. Why does the ATO need a track data base (TDB) for the route’s speed profile? The route’s speed profile is part of the ERTMS Movement Authority, isn’t it?

  4. Hi
    reading this article reminds me of a problem I saw in one of ATOs signaling system once. It was “miss balise” and I wonder if you can suggest the cause. Could it be because of electromagnetic noise? and anyhow how could we test the exictence of EM noise? or what are the other possible causes could be?


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