In the shadow of central Europe’s highest mountain, The Mont Blanc Express line is a narrow-gauge single railway line winding its way just over 55km between Saint Gervais-les-Bains in the French Alps to the Swiss town of Martigny.
Way back when the journey between Geneva and Chamonix took seven and a half hours by cart, the Freycinet Act was passed (1879) to expand the French railway network and build branch lines. The Paris-Lyon- Méditerranée (PLM) railway company was granted the concession to build and run the La Roche-sur-Foron to Chamonix line. The first section, La Roche- sur-Foron to Cluses, opened in 1890 and, after being unable to find a solution to circumnavigate the Prarion mountain, the line was extended only to Saint Gervais.
Rather than the ambitious tunnel initially planned through Mount Prarion, the PLM looked to follow the course of the River Arve around the mountain. Due to the constraints of constructing a line along a narrow mountain valley, the PLM took the decision to build a separate line using metre gauge. This in turn offered the ability to construct curves of tight radii, 150 metres in the French section and as tight as 60 metres in Switzerland.
The new line gave the PLM the chance to test out a pioneering method of electric traction via a third rail. The power was provided by two specially constructed hydroelectric power stations located on the River Arve adjacent to the track and supplied directly to the track at 580V. It proved successful and was introduced on the Saint Gervais to Chamonix section that opened to the public in 1901. To this day it remains one of only two third-rail electrified lines on the entire French network.
On the Swiss side of the border, work on the Martigny to Châtelard line through the Trient Valley commenced in 1902.
This sector was arguably more challenging than the French one. With even steeper gradients of up to 200mm/metre, a 2.5km section of rack and pinion was required to assist vehicles both up and down the slope. The track was laid on steep embankments and specially constructed ledges and through a number of tunnels. In urban areas of the Swiss line, electric traction was provided via a catenary wire. Initially, engineers feared that a build up of ice on the catenary wires would prevent a good contact. Trains did not run throughout the winter until tests proved that the winter weather did not cause the previously envisaged issues. This 19.1km section of the route opened in 1906.
Incorporating the 1883-metre long tunnel under Col des Montets – incidentally the highest part of the route at just short of 1396 metres altitude
– and taking the line right to the French Swiss border, it was another two years until the Chamonix to Châtelard section was completed. This final section thus connected Saint Gervais through to Martigny. The drilling of the tunnel caused a number of engineering headaches, mainly due to fissures and moraines in the rock allowing the passage of large volumes of water. A footpath was provided alongside the track giving pedestrian access through the tunnel. necessary as the two valleys were often cut off from one another after heavy snowfall due to the high risk of avalanches. A feeder wire from one of the existing power stations to sub-stations near Argentière and Vallorcine provided the additional electric supply.
The footpath was removed in the Col des Montets tunnel in 1980, and the track was embedded in concrete to convert it to mixed use. This provides access to freight traffic during periods of avalanche risk when the road over the Col des Montets is closed.
After renewal and re-railing work in the 1950s and 1980s, a project to upgrade the French part of the line was approved during the middle of last decade. Work started in April 2012 with the aim of doubling the current capacity of one train/hr in each direction. It consisted of partial track renewals, 14km of plain line and seven units of S&C, resignalling, electrification improvements, renovation of the Col des Montets tunnel, a bridge renewal and a bridge reinforcement.
Alpine weather conditions constrained some of the construction work to certain times of the year – winter 2012/13 saw a total of four metres of snowfall. The track renewals incorporated formation work during which time new drains were installed. Signalling fibre-optic cables were also laid in preparation for the main resignalling work next year, and the track was re-ballasted and re-railed on new steel sleepers. Throughout the plain line sections, the standard rail section used is 36kg/metre flat-bottom rail. The 18 metre long rails are welded in-situ to create CWR (continuously welded rail) which, owing to the gauge, the rail profile and local rail temperatures, is stressed to 20 ̊C as opposed to the UK standard of 27o.
The S&C is constructed in 50kg/ metre rail. Transition between the plain line and S&C is achieved by installing an intermediate rail of 46kg/metre and placing transition welds at each rail interface. Breather switches are not used between the CWR and the jointed S&C, instead three flexible joints are created allowing longitudinal rail movement.
Plain line renewals, with the exception of small sections between S&C, are predominantly laid on steel sleepers. One sleeper in every five is elongated to include a ceramic support for the third rail. The ‘new’ third rail is reclaimed running rail from the re-railed sections and replaces the former bullhead one at a voltage of 800V.
In tight curves with radii less than 130 metres, ‘Y’ steel sleepers are installed which offer a greater lateral resistance. As the name suggests, these sleepers are Y-shaped with two rail fixings under one rail, and a single chair under the opposite rail. They are constructed of two I-beam cross-section and are interlaced in alternating directions.
At Le Fayet, a new bridge replaced the previous four metre wide brick arch and 72 metres of embankment with a metal and concrete structure. The former was located above what had become a busy road junction and the removal of the narrow underbridge has allowed the remodelling of a safer road layout. The concrete supports were constructed for the bridge and the deck was constructed off site and rolled into position in June 2013.
The line has been totally or partially blocked since April 2012. Work on the renovation of the Col des Montets tunnel should be complete by Christmas. The automatic block signalling is the final tranche of work and is expected to be finished in spring 2014.
Contrary to the name of the line, the journey may not be considered by most as ‘Express’, the 55km will take approximately 1hour 20 minutes. Tucked away in a corner of the Northern Alps crossing the French Swiss border, the history is fascinating and the methods used are interesting. The scenery is without doubt breathtaking, so why rush? Perhaps 80 minutes isn’t quite long enough!
Report by Jane Kenyon