SINCE December 11 2022 passengers have been able to travel along the scenic Golden Pass route between Interlaken and Montreux without changing trains at Zweisimmen, where the standard-gauge Bern-Lötschberg-Simplon Railway (BLS) hands over to the metre-gauge Montreux-Oberland Bernois Railway (MOB). Overcoming this break of gauge has relieved a serious bottleneck on this route, which is vital to the further development of tourist traffic.
Regauging the MOB from metre to standard or laying a third rail for metre-gauge trains on BLS track were never viable alternatives due to the high investment cost. Construction of new infrastructure such as concrete bridges would have also increased CO2 emissions, so the choice of gauge-changing rolling stock is both sustainable and helps to meet climate change goals.
There are two main technologies employed to enable rolling stock to change gauge. One involves the wheels moving on a stub axle, as in the Talgo system first used at the border between Spain and France, while the other is based on moving the two halves of a split bogie frame sideways.
At first glance, this system seems more complex, but offers two distinct advantages. Adapting the height of the vehicle floor to the height of the platform and blocking the lateral movement of the bogie frame halves becomes simple and safe. Trains can use both the BLS platforms which are 550mm-high and the lower 350mm-high platforms of MOB, while lateral movement of the wheels is passively prevented when the train is moving, enhancing safety.
The innovative split-frame concept was developed by former MOB technical director, Mr Jean-Marc Forclaz, and endorsed by former MOB director general, Mr Richard Kummrow, who had a profound understanding of train operation on both metre and standard gauge. It was clear to them that complexity had to be kept to a minimum, and for this reason they chose locomotive-hauled coaches as the solution, hauled by MOB and BLS locomotives on their respective networks.
This avoided the need to install traction, signalling and automatic train protection (ATP) equipment compatible with both railways, but requires the gauge-changing rolling stock to meet the standards and specifications of both MOB and BLS as regards braking systems, couplers, auxiliary power supply, floor height, distance between the internal wheel faces and wheel profile.
For the bogie, compatibility with the two track gauges is ensured by moving sideways the bogie halves with the wheels mounted on them, and by raising the air spring mounted on the bogie cross member from the low to high platform height. For the train, a standard-gauge interface coach coupled to the locomotive is equipped with two coupler types at different heights, and provides connections for braking and auxiliary power supply.
The BLS locomotive hauls the interface coach, a driving trailer, intermediate coach and another driving trailer to Zweisimmen, with the interface coach providing additional seating capacity on this more densely populated section of the Golden Pass route. At Zweisimmen, the interface coach is detached before the three other coaches pass through the stationary gauge-changing facility and the train is then propelled by an MOB locomotive to Montreux. In the reverse direction the train is hauled to Zweisimmen, which is why a driving trailer equipped with a driver’s cab is required at each end of the train.
Construction of new infrastructure such as concrete bridges would have also increased CO2 emissions, so the choice of gauge-changing rolling stock is both sustainable and helps to meet climate change goals.
At the end of 2008 Prose began work to develop a prototype bogie based on MOB’s concepts, while the two companies worked together on a protype gauge-changing facility. Two prototype bogies of welded construction were produced, with the first test runs conducted in 2010 on metre gauge. The focus was on vehicle dynamics as the bogie has only one spring stage and no axles but individual wheels, and ride comfort was found to be good. Testing of the gauge-changing facility proved that the new system worked.
In 2016 Alstom began to develop the bogie for series production, while Prose continued work on the gauge-changing facility. System testing with a gauge-changing train and the stationary facility at Zweisimmen began in 2019, with further optimisation work carried out on the facility in 2021.
Revenue service began in December 2022 with two trains. By this spring, a total of 23 coaches will be delivered in stages, so that three trains can be used in revenue service and one held as a spare. From the end of this year one low-floor vehicle will be added to each train.
How the system works
The gauge-changing facility must perform several functions as the train passes through it, including keeping the bogie position symmetrical to the track centre. The wheels are then unloaded to allow lateral movement with a small force, exerted by pins which are dragged along four groves in the baseplate, which taper in a chevron-like pattern from standard to metre gauge. The fixed wheel distance for the respective track gauge is unlocked allowing the wheels to move laterally. The wheels are then guided along the facility at 15km/h and the wheel distance locked once gauge-changing has been completed.
Conventional metre and standard-gauge vehicles must be able to pass unhindered through the gauge-changing facility, which must also be resistant to frost in a climate where freezing and thawing may occur several times a day. Gauge-changing has to be undertaken correctly with differing wheel diameters and flange thicknesses due to wear, requiring great accuracy in operation and small manufacturing tolerances.
A number of elements move within the bogie during gauge changing. In the first phase, two cantilevers attached to the side of the bogie are folded out, and two pins are lowered for later engagement with the baseplate. The cantilevers are pulled up on ramps by the forward movement of the train. This lifts up one end of the coach and the upper part of the bogie, comprising the transverse beam, anti-roll bar and air spring system. At the same time, locking pins disengage and allow lateral movement of the bogie frame halves.
Once the summit of the ramp is reached, the two bogie frame halves are fully disengaged, and the wheels move along the baseplate on their flanges from one gauge to the other. Lateral movement of the wheels is enabled by the pins engaged in the baseplate. The baseplate exerts lateral force on the pins mounted on the frame halves which push them laterally. Passive and active check rails keep the bogie in the proper position before and during the gauge-changing operation.
In the second phase the cantilevers run down the ramps, the upper part of the bogie is placed on the lower part and the locking pins engage once more. In the locked position, the weight of the coach body prevents vertical movement of the pins which prevents unlocking during normal operation.
The ramps can be folded away to enable wider standard vehicles to pass through the gauge-changing facility. Two pre-tensioned steel strips in the baseplate are pressed down by the wheel flanges that allow standard gauge-vehicles to pass through the facility on their wheel treads rather than on their flanges.
The only moving parts in the system are the cantilevers mounted on the bogie, and the foldable ramps and the active check rails that form part of the stationary gauge-changing facility.
The number of active moving elements was kept low in order to simplify the task of demonstrating the safety of the new system. While the cantilevers are controlled by a system onboard the train, other elements are controlled from the lineside by a system that communicates directly with the railway control centre. There are three modes of operation: automatic, manual and maintenance. In automatic mode, the railway control centre sets the position of the ramps and active check rails.
A particularly challenging aspect of this project was obtaining authorisation to place the new Golden Pass Express fleet into service and approval for the new infrastructure. Existing authorisation procedures in Switzerland are tailored to new vehicles running on existing infrastructure or new infrastructure for existing vehicles. The new gauge-changing system involves innovation in both rolling stock and infrastructure, potentially introducing new hazards. Consequently, the focus during the approval process was on identifying hazards and categorising risks into those which could be assessed against existing standards and those which required specific assessment in order to obtain safety approval. Prose provided assistance to BLS and MOB to obtain permission to introduce this innovative new technology.
MOB has invested SFr 89m ($US 96.9m) in its new Golden Pass Express fleet of 23 coaches built by Stadler Rail and their 58 bogies with gauge-changing capability built and developed by Alstom as well as the stationary facility that was developed by Prose. The railway is not in a position to provide a figure for the increase in passenger traffic that the new through service is expected to generate, saying that the state of the tourist market in the current geopolitical climate and following the Covid-19 pandemic makes forecasting too uncertain.
However, MOB does say that overcoming the break of gauge at Zweisimmen has fulfilled a century-old dream to create a seamless link between the major tourist centres of Montreux, Gstaad and Interlaken, and that a through service without the need to change trains is a “sine qua non” for tour groups.MOB is convinced that it is now well-placed to offer passengers the opportunity to enjoy in comfort some of the best scenery that Switzerland has to offer.