The Gotthard base rail tunnel, the world's longest, came a step closer to completion on Wednesday, as another two sections were joined up.
The tunnel boring machine broke through the last metres of rock between Erstfeld and Amsteg at the northern end.
The breakthrough occurred about half a year ahead of schedule. The machine took only 18 months to bore through 7.2 kilometres.
The tunnel contains two tubes. Wednesday's breakthrough was on the western tube; the eastern one was broken through in the middle of June, also six months early.
Nearly 91 per cent of the entire tunnel system has now been bored. The main breakthrough, between Sedrun and Faido at the southern end, is expected to take place at the end of 2010 or early in 2011.
The tunnel is due to come into operation at the end of 2017. It will be 57 km long from Erstfeld to Faido, but when the system of dual tunnels and access tunnels is taken into account, construction crews will have built a total length of nearly 152 km.
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