Anyone who has travelled the railways of Switzerland will know that tunnels abound in the alpine regions. Most date back from the late 1800s or early 1900s and were marvellous feats of engineering for that period of time. Provided primarily on north-south routes that connected the country across the Alps, they were often spirals inside mountains in order to gain height before the final crossing near to the summit. As such, the rail routes were circuitous and journey times were lengthy.
The Swiss authorities decided at the start of the twenty-first century that a faster means of crossing the Alps was required and that this entailed building new tunnels much deeper down inside the mountains. So emerged the ‘Base Tunnel’ projects, to both shorten the route and to allow much higher speeds. Beginning with the 34.7km long Lötschberg tunnel that opened in 2007, a bigger challenge emerged with the Gotthard base tunnel that would be longer and needed to carry high levels of traffic.
An article on the control and communications systems in this tunnel appeared in issue 146 (December 2016), just prior to the tunnel opening, but managing the total tunnel operations involves much more than controlling train movements. Running from Erstfeld in the north to Biasca in the south, it is the longest rail tunnel in the world at 57km in length and carefully thought-through processes have to be in place to ensure the best possible safety arrangements with evacuation procedures that are fit for purpose in the event of any emergency.
The IRSE (Institution of Railway Signal Engineers) convention in May 2018 was based initially in Lugano, from where descriptions of the technologies and site visits to the tunnel were provided. The result was a fascinating insight into the factors that make up modern day tunnel management.
Gotthard base tunnel traffic
The route from Zurich to Lugano is part of the main freight artery from northern Europe, including the important ports of Antwerp, Rotterdam and Zeebrugge, through to Italy and its main industrial centres. Getting more capacity on the route with reduced journey times has become vital.
The old Gotthard tunnel, with its circuitous and steep gradients on both the south and north approaches, had become a bottleneck on traffic throughput, hence the need to build and operate the new tunnel.
The specification required the route to accommodate six freight and two passenger trains every hour in each direction, speeds for the freight trains being 150km/h and 250km/h for passenger trains. Achieving this with ETCS Level 2 is nowadays straightforward, hence the provision of this system with its associated GSM-R radio bearer supported on the associated radiating cables.
Driving trains at the maximum permitted speed is part of the traffic planning activity so as to allow extra train paths to be inserted if need be. Not only are the trains more frequent and faster but also longer, enabling greater loads to be transported.
Managing the tunnel
The Gotthard base tunnel is in fact two single bores of generous dimensions to allow for a walkway at train door level for use by maintenance personnel, also for train crew and passengers should any evacuation need to happen. Two intermediate ‘Safety Stations’ at one-third and two-thirds the distance from the portals are provided at locations known as Sedrun and Faido. These accommodate rail crossovers to allow trains to cross to the opposite tunnel if any single line working is needed, an arrangement that is similar to the Channel Tunnel. The stations are, however, much more than just a rail transition.
Each has a separate access tunnel bored into it (around 2km in length) from the outside of the mountain, equipped with an independent ventilation system. This permits access (or egress) to the tunnel independent of the end portals. In addition, cross passages link the two running tunnels at 325 metre intervals to allow escape from one tunnel to the other in an emergency as well as providing space for housing equipment.
The biggest risk is fire, both on passenger and freight trains, particularly the latter if they are carrying dangerous goods, and the safety stations and cross passages are all aimed at evacuating people safely and in the fastest possible time. However, fire precaution measures come first in the planning activities and these include:
- A high level of automation of all tunnel systems including signalling;
- Minimising the amount of ‘active’ equipment in the tunnels, for signalling there are only balises and axle counters;
- Backed-up power systems in a ring formation to ensure continuing equipment operation;
- Sophisticated telecommunication networks to give fixed-line and radio communication, the latter comprising both GSM-R and public 3G and 4G services, all served by resilient fibre optic and IP transmission bearers, plus radiating cable for the various radio systems;
- All trains to be checked before entering the tunnel;
- Monitoring of train speed against planned and possible speeds;
- Keeping a defined distance between trains;
- Containment of smoke and blowing smoke away from evacuation areas;
- Provision of portable rail-mounted tunnel ‘doors’, to further segregate people from any incident and minimise smoke drift.
The evacuation of passenger trains is the most challenging, as this may have to occur in either direction and may involve the reversing of a train. The plans foresee a maximum time of 90 minutes to complete an evacuation, so fire containment has to be designed around this target.
Tunnel control and traffic management
Resilience of the equipment is key to continued operation and safety management. The main control centre for the Gotthard tunnel is located at Biasca, close to the south portal, and is a purpose-built modern secure building. A similar centre exists at the north portal, to ensure the appropriate level of redundancy.
The operating floor looks like most others, with its multitude of display screens, but these are focussed primarily on monitoring and controlling the various tunnel electrical and electromechanical systems, primarily ventilation, power, light and communication, as well as providing the necessary information for the maintenance of these systems.
‘Tunnel Safety’ sits above the normal command and communication systems needed to operate a railway and is structured in a layered approach that can drill down directly to the sub systems if need be. At the highest level is an Emergency Response System, brought into use should any incident occur when it would become the tool of the incident commander in such circumstances. Needless to say, the control centre is staffed on a 24/7 basis.
Traffic management sits alongside the ETCS signalling (the interlockings and radio block centres) and provides an additional set of rules to prevent the signaller from taking any action that would contravene tunnel safety requirements for train movements.
An additional interface known as TAG sits between the TMS and the signalling movement control to continually supervise train traffic. This has the intelligence to recognise an irregular emerging occurrence, followed by an alert to the operator and to finally suggest measures that should be taken to prevent any escalation of the problem. The process is focussed on: prevention –> early detection –> risk containment –> event management –> return to normal. That sounds good, but it is acknowledged that the exact source of a problem is not always known. An example would be a train proceeding at a slower speed than expected, which may or may not indicate a potential problem.
Wayside Train Monitoring System (WTMS)
Mention has been made of checking trains before they enter the tunnel for any dangerous conditions and to provide an appropriate intervention. This is not as onerous as it sounds. The process has taken 10 years to develop and is not solely for the Gotthard tunnel but is (or will be) installed at all the base tunnel locations. The one at Erstfeld, to the north side of the Gotthard tunnel, is typical.
The checks take place at line speed, up to 250km/h for passenger trains, and around 10,000 pieces of rolling stock pass the monitoring system every day resulting in 25,000 measurements from which, typically, 25 alarms are generated. The system checks on:
- Hot axle boxes;
- Wheel load checks including any axle overloads;
- Fire and explosive gas detection;
- Train profile and antenna detection, looking for out-of-gauge loads or loose cladding;
- Dragging equipment;
- RFID – radio frequency identification.
Many of these tests involve proprietary equipment that has been available for years, such as hot axle box detectors, which have four sensors, two outside the running rail and two inside.
Others are less commonplace. Strain gauges attached to the rail will detect wheel flats and incorrectly loaded wagons. Three-dimensional images taken of the train will ascertain any out of gauge obstruction, these being coded red = severe and train to stop immediately and green = safe to proceed but examine train when next it stops. Ideally, the checks should take place sufficiently far away from the portals for a train to be stopped before entering the tunnel
If an alarm is raised, an analysis of the condition is generated to determine the severity of the condition and a message is sent to the train over the GSM-R radio. The control centre operator will decide whether to stop the train, instruct it to reduce speed, or take no action. Any speed reduction requirement should be advised before the train is in the tunnel, this being done by both a verbal message and a change to the ETCS Movement Authority. If the train has entered the tunnel with an alarm raised, then the main consideration is to keep the train moving at reduced speed so as to exit the tunnel.
The alarm system itself must be reliable, with 97 per cent currently being achieved and with a high priority response to rectify any failure. SBB has designed and built the WTMS equipment in-house using commercial equipment for the various components.
Completing the route – the Ceneri base tunnel
The Gotthard Massif is not the only alpine range on the Zurich – Lugano route. There also exists Monte Ceneri to the south of Gotthard, the rail line also having a high altitude tunnel with limited-speed approach routes. Not as dramatic or circuitous as the old Gotthard route, it is nonetheless a limitation and the building of a new Ceneri Base Tunnel is well under way. This will be two 16km single bores, one ‘Safety Station’ midway, the latter not including a rail crossover, and regular cross passages between the two running tunnels.
The tunnelling ‘break through’ was achieved in 2016 and work is proceeding to equip the tunnels with track, power supplies, the overhead catenary, telecommunications and safety systems including the ETCS signalling. Installation work will be completed by mid 2019, allowing rigorous testing to take place during 2020 with an end of year opening.
The project is more than just the new tunnel – the new approach routes at both ends have required the construction of impressive concrete viaducts, major undertakings in their own right. Once completed, a journey time of three hours from Zurich to Milan will be possible, together with a considerable increase in capacity.
In summary, congratulations must be given to the Swiss rail and government authorities for having the vision, commitment and determination to see these projects through to a conclusion. Comparisons with the Channel tunnel will be made, where safety processes also have to be rigorous. Tunnelling under a mountain does not require a service tunnel to be provided but the intermediate ‘safety stations’ fulfil a similar role.