Crossing the Alps in Central Europe has been a challenge for centuries and no more so than for the early railway pioneers. In 1882, after a 10 year construction, the first rail tunnel through the Saint Gotthard Massif opened, being 15km long and connecting Gőschenen with Airolo in Switzerland. It provided a route from Zurich through to Italy. Originally powered by steam traction, it was electrified in 1921 and has been a main route for nearly a century.

With increasing traffic levels and the need to eliminate the gradients to the tunnel approaches, the Swiss embarked on the building of a new deeper and longer tunnel. Alp Transit Gotthard (ATG), the company formed to construct this new Gotthard Base Tunnel, began work in 1999 – final break through happened in 2010.

Commencing with the boring of access shafts and construction of work site galleries to accommodate the boring machines, the tunnel consists of two single-track bores with two crossover points, at 1/3 and 2/3 distance, plus cross passages at 325 metre intervals to house electronic equipment cabinets. These also provide access for track workers and escape routes for passenger use in an emergency.

The maximum depth is 2.3km and temperatures would reach 46oC if forced ventilation were not provided.

The tunnel is 57km long (35.4 miles) and is the longest rail tunnel in the world. It connects the towns of Erstfeld in the north with Bodio in the south and shortens the route by 40km compared to the old tunnel, reducing the transit time from Zurich to Milan and Lugano by around 40 minutes. Electrified at 15kV 162/3 Hz, it will permit passenger trains to run at 250km/h and freight trains at between 100-120km/h.

Commissioned for trial running on 1 June 2016, the new tunnel will be in full commercial service by the end of this year.

A project of this size was never going to be cheap and expenditure of SFr12.8 billion (around US$9 billion) has been incurred. These figures are based on 1998 prices excluding inflation, value added tax and construction interest.

As stated above, construction has been the responsibility of ATG, a wholly owned subsidiary of SBB CFF FFS, the Swiss national railway company.

Signalling the tunnel

The Swiss, despite not being members of the EU, have been strong advocates of ERTMS and have led the way in the development of ETCS. Most lines are now equipped with ETCS Level 1 Limited Supervision (LS), which is a non-continuous train supervision system that protects the train should the driver not react correctly to the lineside signal.

Higher speed corridors, such as the Berne- Zurich and the Loetschberg Tunnel routes, are equipped with ETCS Level 2, giving continuous train supervision via the GSM-R radio link. It was a natural choice, therefore, that the new tunnel should be equipped with similar technology.

Whilst the application of ETCS Level 2 is now reasonably well established for conventional main lines with ‘normal’ tunnels, would the deployment of a system be different in a tunnel of this length? And should any special measures be made to ensure continuity of service?

ETCS Level 2 remains a fixed block system with the block sections being marked by ETCS marker boards. With its GSM-R radio bearer, there is no need for conventional line side signals providing all trains are fitted with the on-board equipment. After a competitive tendering process, Thales was selected to design and supply the ETCS system, including all the signalling peripherals, with a contract that was let in 2008 with a current value of SFr190 million.

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Designing the system

Many decisions had to be made before detailed design work could commence. Spacing of the block sections, and the relationship of these to the issue of Movement Authorities, needed to be determined so as to maximise the anticipated traffic flows. All of this was modelled on a simulation programme devised jointly by Thales and SBB engineers. The result was to have balises spaced at a typical distance of 800 metres inside the tunnel and between 200-400 metres on the approach tracks at each end. This gives an improved safety separation inside the tunnel.

ETCS marker boards (along with Swiss national rail boards) are provided at the balise locations. Movement Authorities can be granted up to a length of 32km but are limited to only a few block sections if trains are running in close headway. Normally freight trains will operate with a 5km separation, rising to 9km (about 10 block sections) for passenger trains owing to their higher speeds. Only one Radio Block Centre (RBC) is provided for the tunnel operation, this being housed at Bodio. Other RBCs are being installed for the whole Gotthard Base Line route and, indeed, for other rail routes in the surrounding area.

Four interlockings are required for the two crossover locations in the tunnel and for crossovers on the approach tracks. The interlockings provide the safety intelligence of the signalling system as well as the safe route setting. The RBC can only allow a Movement Authority if the interlocking has safely set and locked the necessary route.

Thales ELEKTRA 2 interlockings are installed in the equipment buildings at Erstfeld and Bodio. This electronic interlocking design has been in service for around 15 years and has a proven track record. It has full hardware redundancy and operates using two separate data channels, each separately programmed by two teams, from which comparisons are made before the final data configuration is agreed (diverse programming).

Element controllers are installed in the tunnel locations. Whilst train position data is transmitted every 6 seconds via the GSM-R link, independent position information is derived from axle counters, the Alcatel AzLM type being used. Thales absorbed the Alcatel rail signalling interests in 2007, so it was a natural choice. The axle counters are located adjacent to the balises but separated by a minimum distance of 1.2 metres, to avoid any unwanted mutual interference.

The two crossovers within the tunnel are equipped with Hydrostar point machines supplied by Linz-based Voestalpine, allowing a 110km/h turn out speed.

The entire tunnel is provided with a no-break power system based primarily on batteries and invertors and designed to be fully resilient. Similarly, the signalling transmission system is designed as a dual ring (red and green) fibre cable using SDH transmission to give continuous connection and guard against both equipment failure and cable cuts. Thales designed the fibre configuration, with the actual fibre rings being supplied by the Swiss company Alpiq, part of the Transtec consortium alongside Thales.

The operational control centre for the tunnel is located at Pollegio, near to the southern portal of the tunnel. The train control system there is a Siemens-supplied system that will eventually control the whole of the region.

Train fitment

Many trains in Switzerland are already equipped with either ETCS Level 1 LS or Level 2, as well as GSM-R radio. Only those fitted with an ETCS Level 2 capability are permitted to operate through the tunnel.

The ETCS train-borne equipment is supplied by either Alstom, Siemens or Bombardier, and all trains will be retro-fitted with Level 2 equipment.

A new fleet of 250km/h trains, to be supplied by Stadler Rail, will come fitted with Level 2 at the factory.

Since the tunnel is required to facilitate public mobile communications (see below), the trains have to be fitted with repeater equipment to enhance the signal within the carriages. This repeater is manufactured by Commscope, a global leader in infrastructure solutions for communications networks, which is supplying the ‘In Train Com’ company as part of a joint venture with the public mobile operators to work with SBB and the train build companies.

Telecommunications

A tunnel of this importance inevitably has a comprehensive telecom network supporting both rail operations and public requirements. The fully resilient fibre optic cable network was supplied as part of the power provision contract of the tunnel construction consortium (TTG), which specified the cable parameters using various specialist companies to assist with the task.

Once installed, the provision of the associated transmission was entrusted to Nokia as the system integrator using IP/MPLS Multiprotocol Label Switching telecommunications technology. Nokia, also a member of the Transtec consortium, was already involved in supplying GSM-R equipment to SBB prior to the Gotthard Tunnel project so was well known to the client.

Photo: SBB.

Photo: SBB.

Telecom requirements come in three parts. The fixed line, data and servers networks using multi service Ethernet over IP/MPLS technology, support the tunnel communication requirements. These include IP phones, emergency call points, video surveillance and a public access system including loudspeakers. The latter led to a problem with reverberations in the long thin ‘tubes’ in the two multifunction stations Sedrun and Faido – only overcome by adhering sound absorbing material to the tunnel wall.

Connections of the 19 sub-control systems to the SCADA-based tunnel control systems provide for alarm gathering, network management, power supervision remote monitoring and many others. During simulations, it became evident that there would be over 150,000 datapoints with sensors even being able to trace loose connections. Every door, light and air vent is supervised from the control centres in Erstfeld and Pollegio. The comprehensive system is designed to cope with all scenarios including emergency situations and was supplied by Siemens as a sub-contract to Nokia.

The tunnel radio system, based on radiating cable (leaky feeder) in both tunnels, has a length of 120km and is sectioned into 900-metre lengths. This is a backbone for all radio services with SBB doing the functional specification and Commscope providing much of the hardware as a subcontractor to Nokia.

The provision of public internet access is achieved by ATG/SBB in conjunction with the three Swiss mobile operators – SALT (pre Orange), Sunrise and Swiss Com. SBB is contracted to provide the infrastructure for the mobile operators who then provide the 3G and 4G services. These operate on the 900Mhz, 1.8GHz and 2.1 GHz bands.

GSM-R

The radio bearer for ETCS, GSM-R, is a vital part of the communications network. SBB took on the responsibility for the provision of GSM-R and achieved this with a contract awarded to Nokia.

The GSM-R radio system is borne upon the same radiating cable as that which carries the public cellular services. The system is split into 900-metre sections, meaning that 32 base stations (BTS) are needed.

The initial design was built and configured in an SBB test laboratory with two base station controllers and three BTS. This tested out the dual redundancy arrangements and the handover scenarios in simulated tunnel conditions as well as the Radio Block Centre connection and the functionality for ETCS.

With both Nokia and SBB satisfied, installation commenced in the two tunnels with the system progressively commissioned ready for the opening in mid 2016.

Currently controlled over the SBB SDH (Synchronous Digital Hierarchy) transmission network, the GSM-R system will migrate to the IP data network also being provided by Nokia in due course.

The approximate value of the telecom element of the control and communications contract is less than 10 per cent of the whole railway technology delivery contract from Transtec Gotthard.

Degraded mode operation

Whilst the signalling and communications systems have been designed for maximum reliability and availability, there could always be the odd occasion when the systems fail.

With the near certainty of trains being in the tunnel should this happen, measures have to be in place to ensure train movements can still be made. This is known as Staff Responsible Mode whereby trains can be driven, not under the supervision of the RBC, at a maximum speed of 40kph.

In extreme conditions, trains are permitted to be driven ‘on sight’ even if the communication path is also failed.

Should the failure be a train breakdown, then operational procedures are prepared for a rescue locomotive to be signalled into the tunnel to assist the failed train.

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Safety verification and system testing

In 2010, the main system components were assembled in the Thales laboratory in Zurich so as to prove the integrity of the design.

Installation could then begin and, in 2013, field tests were commenced which included the GSM-R communication link. Thales, the tunnel construction consortium (TTG) and the client (ATG) were involved with this, later to be joined by SBB technical staff who performed their own separate tests as well.

As with all modern day safety requirements, a verification and validation exercise of the system was necessary, this being carried out by Thales. An assessment of the Safety Case requirements covering the four separate elements – RBC, Interlocking, Train Control and Whole System – was contracted to a specialist assessment company in Vienna.

Completing the route

The Gotthard Base Tunnel is not the only major upgrade on the new route from Switzerland into Italy. South of the Gotthard tunnel is the Monte Ceneri, another mountain crossed by an old high-level tunnel. The 15.4km twin-bore Ceneri Base Tunnel is currently under construction, with breakthrough being achieved in January 2016.

The control and communications systems are expected to be broadly similar to those in the Gotthard tunnel but the technology for this engineering of the project is being provided in four separate elements – track and logistics, electrification and telecommunications, the tunnel control system and signalling. Installation and fitting out has begun, with completion expected in December 2020.

The Ceneri Base Tunnel will run from Camorino to Vezio near Lugano and, like the Gotthard, it will shorten the route as well as allowing much longer and faster trains to operate, reducing the transit time by a further 20 minutes.

The renaissance of rail during the last 20 years has resulted in a number of major infrastructure projects to increase capacity and line speed. These have created new engineering challenges, including within the control and communications sector. The Gotthard Base Tunnel is within the ‘big league’ of these and, once the full service is introduced, many eyes will be watching to see if the technologies are able to deliver the predicted business improvements.

Written by Clive Kessell