Despite speculation to the contrary, SNCF Réseau and its contractors are continuing to roll out the NExTEO communications-based train control system which will manage the extended RER Line E in Paris, as project manager Jérôme Lefebvre explains to Jérémie Anne.

Later this year, infrastructure manager SNCF Réseau expects to start dynamic trials and commissioning of the NExTEO communications-based train control system being developed for use on Paris RER lines E, B and D. Project Director Jérôme Lefebvre reports that installation of the lineside equipment has recently started, building on the output of a long research and development programme.

The Paris project teams are tackling the same technological challenge as London’s Crossrail project and the deployment of CBTC on the København S-bane, both of which were significantly delayed by the complexity of the signalling and train control interfaces. Lefebvre emphatically refutes the suggestions circulating in local media last year that the NExTEO project had been abandoned, confirming that the technology is now in the testing phase, including the first trials of automatic train operation on the national rail network.

The region around the capital is by far the busiest part of the French rail network, with 40% of all trains and 70% of the passengers being carried on just 10% of the total route length. Lefebvre explains that this unique concentration was why the SNCF group opted to develop bespoke equipment and systems for this densely trafficked area.

In addition to dedicated operational rules, SNCF initiated a programme to look at operating suburban and cross-city trains using tools and technologies specifically adapted to the challenges of mass transit. This began life in 2010 as the so-called Next project, which became NExTEO in 2014.

Designed to support attended automatic train operation to GoA2, NExTEO is similar to other CBTC systems, incorporating ATP with moving block functionality and automatic traffic supervision as well as ATO.


Photos: Jérémie Anne

The RER Line B starting signal at Chatelet, looking towards Paris Nord. This section of route will be equipped with NExTEO as part of the roll-out on the core of lines B and D.

From metro to heavy rail

Lefebvre points out that there are many challenges in transferring CBTC technology from a metro environment to the more demanding heavy rail network. Most metro lines operate as a closed system, with trains that are typically around 75 m long and weighing 200 tonnes, carrying up to 800 passengers at a maximum speed of 80 km/h.

By contrast, the double-deck RER NG trains, which will be the only type equipped to operate on Line E, are 112 m long and can run at up to 120 km/h. They will be capable of operating in multiple, with a full 225 m train carrying a crush load of up to 3 000 passengers weighing no less than 900 tonnes. As such, the traction and braking characteristics for automated operation will be very different from a metro train.

The implementation conditions are also very different, as many RER services operate over shared routes that have to be kept open for other rail traffic. This is unlike a metro, where it may be possible to suspend the service for periods to facilitate the resignalling work.

The NExTEO concept was initially conceived within SNCF Réseau, in consultation with Paris metro operator RATP and various signalling suppliers. In 2016 a contract was awarded to a consortium of Siemens Mobility and Atos for the technical development and industrialisation, along with deployment on the central section of RER Line E from Pantin to Nanterre-La-Folie. The objective of this initial project is to support a high traffic flow through the central section of the line, with a minimum headway of 108 sec between trains, and a maximum speed of 120km/h between Porte Maillot and Haussmann-Saint-Lazare.

Lefebvre says the implementation of NExTEO represents a step change from the signalling systems used on existing lines, adding that deploying the equipment in an open environment ‘is a real challenge’.

Additional complexity is introduced by the fact that RER Line E trains will not originate in the central section, but will arrive in the cross-city core from suburbs on both sides of the greater Paris metropolitan area. On their approaches, they operate on sections of the rail network that carry a wide mix of traffic, including freight, high speed and regional passenger trains.

Lefebvre emphasises that SNCF Réseau is keen to ensure that Line E services arrive in the right order to pass through the Pantin – Nanterre core, even in the event of operational disruption. So in addition to NExTEO, the project will see the installation of an ATS+ traffic supervision system on certain sections of Line E that will not be equipped with CBTC, notably from Pantin to Val-de-Fontenay and Le Raincy in the east. These sections cover 700 signals and 640 point ends. This is also being supplied by the Siemens Mobility-Atos consortium.

Once deployed, the ATS+ will oversee all the trains running in the area: RER Line E services and high speed trains to and from Paris Est, Transilien route P suburban services, long-distance TERs serving the Grand Est region and freight trains.

The traffic management system will initially work with the existing KVB automatic train protection system on the surface tracks to the east, but an enhanced version designated KVB-p will be used on the western extension. In the longer term, SNCF Réseau envisages that both would be replaced by interoperable ETCS.

Lefebvre explains that the RER trains’ transition from the conventional signalling and traffic management system to NExTEO as they approach the core ‘will be fully automatic’. The trains will make a dynamic transition to CBTC on the approaches to Nanterre-la-Folie in the west and Pantin station in the east. To facilitate the eventual migration from KVB to ETCS, the NExTEO onboard system is based around an ERTMS-compliant EVC, using Specific Transmission Modules for both the CBTC and KVB.


The RER NG double-deck EMUs are the first trains to be fitted with NExTEO onboard equipment.

Project management

As NExTEO is a major innovation, Lefebvre insists that it is both a technological and human challenge. To this end, he says SNCF Réseau has adopted an innovative project management approach. Progress is punctuated by a number of gateways, all of which have to be passed before the equipment is put into service. As long as a stage has not been mastered by the SNCF teams and those of Siemens-Atos, the project does not move on to the next. It is only when each gateway has been fully completed that the project will move forward.

All of the safety assurances need to be put in place, particularly those related to moving block operation, before the NExTEO system can be put into commercial service. Lefebvre notes that Crossrail adopted much the same project management approach.

‘All of the safety assurances need to be put in place, particularly those related to moving block operation, before the NExTEO system can be put into commercial service’

As an initial step, the infrastructure manager deployed a digital simulator that reproduces the NExTEO-equipped section of the RER E with a high degree of precision. This enabled a large number of tests to be carried out while the system was being developed, to ensure that it would meet the operational requirements.

The next step was to develop a dedicated NExTEO test centre at Gagny, which Lefebvre says has been ‘very precious’. It has been in operation since the end of 2021, with two dedicated RER NG trains operating over sections of track that have been reconstructed to provide a faithful representation of a section of line equipped with NExTEO. The test programme has now reached the stage of automated driving, which Lefebvre says was the first practical trial of GoA2 on the French national rail network.

With testing well advanced, he reports that installation of the lineside equipment on the core of Line E is now getting underway. The first of about 150 radio antennas that will be needed to cover the Pantin – Nanterre core have recently been installed, while work has also started on the installation of 900 balises, along with the related cabling and connections to the local interlockings. Balise readers are being fitted to the trains, which will augment the onboard odometry system to provide accurate position location.

While much of the development work has been undertaken at Gagny, Lefebvre explains that the final testing will have to be carried out in situ and it will be necessary to undertake some ‘hand-stitching for the periods when we need to go onto the tracks or into the signalboxes’. He points out that ‘access to the infrastructure is a scarce resource, as more than 1 500 trains circulate in this sector every day’.

Services on Line E will be interrupted at night and at weekends in order to carry out testing and final commissioning. The whole Pantin – Nanterre section will be closed for several weekends in order to undertake complete dry runs of the NExTEO equipment. This work is due to be completed in the summer of 2023, with dynamic testing starting after that.

Overlapping services

While construction and fitting out of the LineE extension from Haussmann St-Lazare to Nanterre is well advanced under the EOLE scheme, Lefebvre explains that NExTEO is not essential for the commissioning of this section. When the extension opens, the trains currently terminating at Haussmann will be extended to Nanterre, with a maximum of 16 trains/h at peak times.

The critical deadline for NExTEO will be the opening of the second phase of EOLE from Nanterre to Mantes-la-Jolie. This will see the number of trains running through the core increasing to a maximum of 22 trains/h in each direction. The 16 trains to and from the east, which turn back at Nanterre, will be augmented by a further six trains per hour serving the western suburbs, running to and from Mantes-La-Jolie and terminating at Rosa Parks.

Under the so-called ‘overlap’ service, the two traffic flows will be superimposed to provide a more intensive operation in the central tunnel, which will by then need to be equipped with NExTEO. Lefebvre says the system has been specified to handle up to 28 trains/h in each direction at a later stage.

The whole of RER Line E from Mantes-La-Jolie to Chelles-Gournay and Tournan-en-Brie will be controlled from the so-called Unified Command Centre at Pantin, which was put into service in February 2022. This brings together in a single location all the functions relating to the provision of services on Line E. Describing the CCU as a ‘jewel of technology’, Lefebvre comments that this east-west control centre for the Paris region will control 3 000 trains per day when it is fully commissioned, of which 700 will be Line E services. This equates to approximately 20% of all French rail traffic. By comparison, he notes that the Elizabeth Line service through London’s Crossrail core is regulated from three different locations.


The driving cab of an RER NG trainset.

Lines B and D next

According to Lefebvre, the introduction of NExTEO on Line E represents ‘the showcase of know-how in mass transit’. A successful deployment will pave the way for the technology to be introduced on other parts of the Paris suburban network, notably RER lines B and D.

This project will be ‘a second first’, he says, explaining that it will be undertaken as a partnership between SNCF Réseau, SNCF Voyageurs and RATP. The aim is to improve throughput in the core north-south tunnel between Paris Nord and Chatelet-les-Halles, which is shared by the two lines, and is already one of the busiest railway tunnels in the world. The objective is to accommodate 32 trains/h in each direction at peak times: 20 for Line B trains and 12 for Line D.

NExTEO is to be deployed on Line B from Saint-Rémy-lès-Chevreuse and Robinson in the south to Sevran-Livry and Sevran-Beaudottes in the north. Line D trains will use the system between Villeneuve-Saint-Georges and Stade-de-France-Saint-Denis. One of the challenges of this project will be to manage the co-ordination of the two lines as the services approach the tunnel. Lefebvre explains that this is why NExTEO is expected to be deployed over a wider section than just the Chatelet – Nord core.

Although last year’s press rumours suggested that this second project would also be abandoned, Lefebvre insists that this is not the case. He confirms that tendering for the scheme is now underway, but no more precise details can be given at this stage for reasons of confidentiality.