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A guide to the key vocabulary of the Lyon-Turin project: engineering terms, names and acronyms of the public bodies involved and extraordinary administrative arrangements. Each key word introduces a topic to be explored in order to deepen the understanding of the project and its implications.

Access adit

Carriageway tunnel connecting the twin-tube to the outside. The Lyon-Turin base tunnel has four of them, one in Italy and three in France, with three functions:

  • Geognostic survey to discover the characteristics of the rock before starting the tunnel excavation works
  • Logistic access route for the boring machine during the excavation of the twin-tube
  • Emergency safety exit and access route for maintenance vehicles once the base tunnel becomes operational


This acronym stands for Agence de Financement des Infrastructures de Transport de France, a French public administration body whose mission is to finance national transport projects. It allocates funds on an annual basis for the cross-border section of the Lyon-Turin railway line, according to French law.

Base tunnel

This is the twin tunnel through which the trains travel. It is referred to as the “base” tunnel because it is excavated at the base of the mountain, almost without a slope (around 12 per thousand), to distinguish it from the existing tunnels, built at the end of the 19th century at the top of the mountain so that the excavated stretches were shorter. In the case of the Lyon-Turin, the base tunnel passes under the Moncenisio, it is 57.5 km long and consists of two parallel tunnels (twin tunnel), one for each direction of travel, in accordance with modern rail safety standards.


They are small connecting tunnels between the two parallel galleries that are the structure of the twin-tube. They are used to facilitate any safety evacuations required. Along the 57.5 km of the Lyon-Turin base tunnel, there will be 204 safety by-passes, one every 333 meters.


This acronym stands for Connecting Europe Facility, also known as the European Interconnection Mechanism (EIM). It is a seven-year funding program for EU infrastructure investments in transport, energy and digital projects aimed at achieving increased connectivity between Member States. This is the European funding framework for the cross-border section of the Lyon-Turin railway line.


This acronym stands for Climate, Infrastructure and Environment Executive Agency, a European Commission body for the financing of the TEN-T network, which aims to implement the efficiency of the technical and financial management of the projects.


‘French-Italian Intergovernmental Commission for the Lyon-Turin railway link’.
This is a body set up by the French and Italian governments following the Treaty signed on 15 January 1996 in Paris for ‘the construction of the new Lyon-Turin railway line’. Its task is to preside over the activities necessary for the definition, realisation and management of the Lyon-Turin railway line, exercising, on behalf of the states, firstly functions of direction, study, in-depth study and elaboration, then, with the institution of the Public Promoter, of supervision and control over its activities in the project preparation phase, the execution of the preliminary works and now in the phase of contracting and realisation of the work.


This acronym stands for the Interministerial Committee for Economic Planning and Sustainable Development, a collective body of the Italian Government that completes the authorisation procedure and gives the green light to the financing of projects on the list of “priority public works” (formerly the Objective Law), including the Lyon-Turin tunnel, that has approved the definitive project of the cross-border section and the construction site variant.

Conveyor belt

This is a device used for the automatic transport of the excavated materials from the excavation face to the outside storage and sorting sites. It runs on electricity and makes it possible to replace the use of trucks both inside and outside the tunnel, with obvious advantages in relation to safety and the environment.

Cross-border section

The cross-border section of the Lyon-Turin is the route between Susa (in Italy) and Saint Jean de Maurienne (in France) for which the public promoter TELT is responsible. It is 65 km long and 89% travels through tunnels. It connects the two national side of the entire route, the Italian side (between Bussoleno and the Turin node) under the responsibility of RFI and the French side (between Saint Jean de Maurienne and Lyon) under the responsibility of SNCF.

Cut-and-cover tunnel

This is the artificial gallery that will be the French entrance to the base tunnel. It is a concrete “box”, which allows trains to pass under the A43 motorway and the RD1006 road, and then enter the mountain.

Démarche Grand Chantier

This is an exceptional initiative of the French State granted to the Lyon-Turin construction site in France, following the decision of the Comité Interministériel d’Aménagement et de Développement du Territoire in December 2003. It has two objectives: to prepare and accompany the construction site before, during and after the work process, allowing the integration of local and external companies and employees; to root the project in the Maurienne area, so as to involve the territory and promote positive effects.


Excavated of spoil/ excavated materials

This refers to the waste material after excavation, which is loaded into muck cars that travel on a conveyor belt, the composition of which is immediately identified for waste classification purposes. In the case of the Turin-Lyon, the waste is subject to several checks, in order to verify and select the materials that can be reused, for example to make reinforced concrete or similar products (at least 50%). The material that cannot be reused for the project is still, however, assessed for the purposes of environmental recovery of disused quarries, or stored in repository areas identified in the project. Unsuitable residual materials are classified as waste and stored in authorised landfills.

Exploratory tunnel

This is a pilot excavation that gives rise to in-depth analysis of the soil and/or the mountain in order to obtain information of its composition at a geological level.


Grant Agreement (GA) 

This is the contract between the European Union, Italy and France that allocates and regulates the provision of EU financing tranches to the cross-border section of Lyon-Turin. It is signed by the States within the scope of the Connecting Europe Facility (CEF) program.


Historic line

This is the line currently operational connecting Italy and France and along the route it includes the Fréjus tunnel, a 13 km tunnel which is 1,300 metres above sea level and was inaugurated in 1871. An important technological innovation at that time, witnessing the first ever mechanised excavation of a railway tunnel that no longer meets international transport standards and therefore needs to be replaced by the base tunnel.


Interchange niches 

These are service areas excavated along the sides of the La Maddalena tunnel in Chiomonte, Italy’s largest Lyon-Turin construction site. There are 23 niches (3 m deep and 30 to 40 m long) which are designed to facilitate the transit and reversing of construction vehicles working on the excavation of the base tunnel. The La Maddalena tunnel, created for geognostic purposes, will subsequently be turned into an access adit and ventilation shaft for the base tunnel.

International station

This is the end of the Lyon-Turin cross-border section: in Italy the station is in Susa, in France it is in Saint-Jean-de-Maurienne. There will be two multimodal stations, also used by the existing train line and buses, and there will be parking for bicycles and motorcycles. The stations will be the hub on which sustainable mobility solutions for summer and winter tourism of the two Valleys will converge. 


Knock-on effects 

Within the context of the Lyon-Turin project, specific reference is made to the “economic knock-on effects”, i.e. the indirect effects of the work which support the development of the economy. In Italy, €1 spent on the realisation produces a knock-on effect of €3.77 on GDP (source: Clas Group)


Mechanised excavation

This refers to one of the excavation modes of the Lyon-Turin tunnel. It foresees the use of a TBM.

Mediterranean Corridor

It is one of the nine priority axes of the trans-European transport network (TEN-T). Its route between Budapest (Hungary) and Algeciras (Spain) covers a distance of 3,000 km connecting, from east to west, 7 EU corridors, passing through six European countries (Spain, France, Italy, Slovenia, Croatia and Hungary).


Open-air works

The final works on the cross-border section of the Lyon-Turin railway line are partly carried out in the tunnel and partly in the open air. Open air works mainly refer to the entire complex of works for international stations, the railway interconnections of the base tunnel with the historic line and all works in the Susa valley in Italy (including the transfer of the airport) and in St-Jean-de Maurienne in France.


Pact for the territory

This is a program aimed at turning the Lyon-Turin construction sites into a development driver for the economy of the territories affected by the construction of the infrastructure. Signed in 2018 between Piedmont Region, the public promoter TELT and the Lyon-Turin Government Commissioner, it imposes the objectives of the Démarche Grand Chantier to be included within the Italian regulatory framework. Within the scope of this project, TELT undertakes to include a social clause in all its calls for tenders as a criterion for the selection of tenders, which relates to the recruitment of disadvantaged and very disadvantaged workers. Rewards are also granted to companies that offer workers logistical solutions that encourage the reduction of environmental impact (in terms of air and noise quality). To conclude, full information on the construction sites and works and total transparency concerning companies and tender contracts are also guaranteed.


Refuge Chamber

This is a container-type structure that plays a fundamental role for the safety of underground construction sites: providing protection to people in dangerous situations in tunnels, in particular when it is impossible for them to reach the outside. They are located every 300 m along the tunnel under excavation (also on the TBM), and equipped with oxygen cylinders and signalling devices; it has a maximum capacity of 18 people.



These elements are made of concrete and used for lining the tunnels excavated with TBM. In the case of the Lyon-Turin railway line, they are produced in special sites using aggregates obtained from the excavation of the tunnel. All suitable excavation materials are transformed into concrete and then into segments. They are positioned directly by the TBM by means of suction cups. The segment factory is the industrial production site for prefabricated concrete tunnel lining elements. These segments are produced using good quality aggregates obtained from the excavation of the tunnel.

(Geognostic) Surveys

In layman’s language, soil or rock samples are taken to verify their composition and structure. They can be carried out to define the geological profile of the mountain, or even during the excavation advancement phase to confirm the forecasts.



This acronym means High-Speed Train (Treno ad alta Velocità) It is also used to refer to lines and infrastructures (tunnels and stations) that allow passenger trains to reach a speed of 250 km/h. in Europe. The AV (HS) lines can accommodate freight trains, for this reason it is also referred to as AC (HC), i.e. high capacity.

TBM / Boring machine

This is the machine used for mechanised excavation in the tunnel; the so-called “head” of the boring machine, which works by means of rotating cutters that erode the mountain rock, performs the excavation. It is commissioned ad hoc depending on the type of excavation to be carried out (lengths, rock, etc.) and, in addition to drilling the rock, it also conducts geognostic surveys during work in progress to verify the composition of the mountain rock as it advances. It also loads and positions the tunnel lining segments, and houses the small “workshops” of workers and craftsmen.

It is a tradition in the underground works industry to give the TBM a female name. In the case of the Lyon-Turin tunnel, a total of 9 boring machine are being used.

Technical observatory for the Lyon-Turin

This is a body established by the Presidency of the Council of Ministers in December 2006, to accompany the entire process of defining, sharing and performing the interventions required to adapt the Lyon-Turin Railway Axis. In particular, it carried out the works which led to the shared drafting of the definitive plan and continues its consultation with the territories during the work in progress with the task of managing any impact within the territory.

TEN-T Network

This is the network of trans-European transport infrastructures established by the European Union to promote the seamless movement of persons and goods. It consists of 9 Corridors: Baltic-Adriatic Sea, North-Baltic Sea, Mediterranean, Orient/East Mediterranean, Scandinavian-Mediterranean, Rhine-Alps, Atlantic, North-Mediterranean Sea, Rhine-Danube. They connect the different areas of Europe horizontally and vertically in a single integrated, multimodal transport network: the completion of the Core Network is planned for 2030.

Traditional excavation

This refers to one of the excavation modes of the Turin-Lyon tunnel. It foresees the use of explosives or wrecking ball, with subsequent reinforced concrete cladding, and is used in areas with particular geological characteristics (e.g. unstable rocky masses) or for the connection branches between the twin tunnels.

Tunnel access

This is the access point to the tunnel that will be used by trains; on the Italian side it is located in San Giuliano di Susa; on the French side in Saint-Julien-Mont-Denis. 


The Lyon-Turin base tunnel consists of two parallel tunnels, one for each travel direction of the trains; hence, the term twin-tube used in the technical field.

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