Good to knonw
The RhB winds its way uphill
A masterpiece of pioneering railway
Harmoniously embedded in its natural surroundings, the Albula Line is an outstanding example of railway engineering at its best – which is also why it is ranked among the UNESCO World Heritage "Rhaetian Railway in the Albula / Bernina Landscapes". Opened in 1904, the entire track between Thusis and St. Moritz took just five years to build and is today regarded as a masterpiece of railway engineering and routing. Of particular note is the section between Bergün and Preda, as this proved exceptionally challenging for the engineers building the mountain railway.
Helical and spiral tunnels replace rack railway
Between Bergün and Preda, engineers were faced with the drawback of a 416-metre difference in height across a valley measuring only approx. six kilometres in length. As a result, they were reluctant to install a section of rack railway. In order to keep to the specified maximum gradient of 35 per cent yet still overcome the huge difference in height, the track had to be twice the length of the valley. The railway pioneers achieved this using helical and spiral tunnels: with two helical tunnels, three spiral tunnels and four bridges, the railway climbs from 1,373 metres in Bergün to 1,789 metres above sea level in Preda.
Helical and spiral tunnels differ in that the tracks in a helical tunnel form a semicircle so that the train runs in the opposite direction on exiting the tunnel. If such a turn leads into open terrain, this is known as a loop line. However, if the railway line makes a 360-degree turn in the mountain while spiralling upwards, this is called a spiral tunnel. Pegging out these helical and spiral tunnels proved particularly challenging during the course of construction. However, using fixed points outside of the tunnel and angle measurements with theodolites – special instruments for measuring angles – maximum precision could easily be achieved: any variations in length and direction were just a few centimetres.
The angle measurements between the fixed points were conveyed and specified at each stage while taking into account the required circular arcs. The red trains of the RhB thus continue to run through the two helical tunnels Plaz and God plus the three spiral tunnels Rugnux, Toua and Zuondra from Bergün to Preda.
The history of the RhB
For more on the development of the spiral and helical tunnels plus many other fascinating stories from 125 years of RhB, see our multimedia anniversary book. An inspiring kaleidoscope of magazine, book and DVD.