There is finally light at the end of the world’s longest rail tunnel, which is set to open next week after almost seven decades in the planning. The 35-mile Gotthard Base Tunnel (GBT), which runs under the Alps in Switzerland has finally been completed. Staff confirmed the transport link is due to open officially on June 1. But the idea to build it was born 69 years ago – Swiss engineer Carl Eduard Gruner first came up with the concept in 1947. Carl Eduard Gruner predicted the visionary project could be finished by the start of the 21st century – and he turned out to be off by just 16 years. His paper was called “Journey through the Gotthard Base Tunnel (GBT) in the year 2000” – and this week his idea will be realised when the tunnel is unveiled. The GBT aims to transform travel through the heart of Europe. When it officially opens on Wednesday, it will overtake Japan’s 53.9km Seikan tunnel as the world’s longest train tunnel and bump the 50.5km Channel Tunnel linking England and France into third place. Some 2,400 workers constructed the 57km GBT, which cost just over 12 billion Swiss francs More than 28 million tonnes of rock had to be excavated from the mountain near the Gotthard pass. The tunnel runs from Erstfeld in the central Swiss canton of Uri, to Bodio in southern Ticino canton. It will shave the train journey from Zurich to Milan in northern Italy down to two hours and 40 minutes, about an hour less than it currently takes. The new route also aims to make rail freight more efficient – it will support heavier cargo and should reduce the number of diesel-guzzling lorries on the roads. The number of daily rail passengers is also set to rise from the current rate of 9,000 people to 15,000 by 2020. It is hoped that the new tunnel will also lead to a growth in day-trip tourism and higher property values in nearby areas thanks to increased accessibility. German Chancellor Angela Merkel, French President Francois Hollande and Italian Prime Minister Matteo Renzi, along with Swiss officials, are due to attend Wednesday’s grand opening. Full service starts in December. The GBT has been viewed as a trailblazer for a high-speed rail link between Turin in northern Italy and the French city of Lyon, which has faced delays and opposition from environmental groups.