An employee of AlpTransit Gotthard Ltd and a visitor stand at the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

Workers use finishing trowels to plane fresh concrete on the track bed of the rails in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

A worker adjusts a laser measuring gauge during the installation of the railway tracks in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

Workers use torque wrenches to fix screw nuts during the installation of the railway tracks in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

Guests waves at a train that has crossed the tunnel during the opening ceremony of the NEAT Gotthard Base Tunnel, the world's longest and deepest rail tunnel, near the town of Erstfeld, Switzerland June 1, 2016. The 57.1-km (35.5 mile)-long Gotthard Base Tunnel, 17 years under construction and designed to last a century, is part of a 23 billion Swiss franc (23.1 billion USD) infrastructure project to speed passengers and cargo by rail below the Alps, as much as 2.3 km (1.7 miles) under the mountain chain, that divides Europe's north and south. REUTERS/Arnd Wiegmann - RTX2F4E5

Image used for illustrative purpose. A worker stands on the special train 'Helvetia' in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. The train, which is 481 metres (1578 ft) long and weighs 787 tons, is constructed to produce concrete for the installation of the railway tracks in the tunnel. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles ) REUTERS/Arnd Wiegmann

Image used for illustrative purpose. Workers drive on a special vehicle during the installation of the railway tracks in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

Image used for illustrative purpose. Workers use torque wrenches to fix screw nuts during the installation of the railway tracks in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012.

A worker use torque wrench to fix screw nuts during the installation of the railway tracks in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

Journalists stand on a platform at a multifunction and emergency stop station of the NEAT Gotthard Base Tunnel during a media visit near the town of Sedrun, Switzerland March 10, 2016. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016, consisting of two parallel single track tunnels, each of a length of 57 km (35 miles). REUTERS/Arnd Wiegmann - RTSA67U

An employee looks at monitors to control the mixture of concrete on the special train 'Helvetia' in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. The train, which is 481 metres (1578 ft) long and weighs 787 tons, is constructed to produce concrete for the installation of the railway tracks in the tunnel. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

Workers cycle past the northern entrances of the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

Image used for illustrative purpose. A worker stands on the special train 'Helvetia' in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. The train, which is 481 metres (1578 ft) long and weighs 787 tons, is constructed to produce concrete for the installation of the railway tracks in the tunnel. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles ) REUTERS/Arnd Wiegmann

Image used for illustrative purpose. Workers joke during a break beside the special train 'Helvetia' in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. The train, which is 481 metres (1578 ft) long and weighs 787 tons, is constructed to produce concrete for the installation of the railway tracks in the tunnel. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

Image used for illustrative purpose. A worker prepares tools and material during the installation of the railway tracks in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

(L-R) France's President Francois Hollande, Germany's Chancellor Angela Merkel and Switzerland's President Johann Schneider-Ammann look on after travelling through the Gotthard Rail Tunnel, the longest tunnel in the world, on its opening day, at the southern portal in Pollegio, Switzerland, June 1, 2016. REUTERS/Peter Klauzner/Pool - RTX2F5PP

Workers sitting on the special train 'Helvetia' distribute fresh concrete on the track bed of the rails in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. The train, which is 481 metres (1578 ft) long and weighs 787 tons, is constructed to produce concrete for the installation of the railway tracks in the tunnel. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles ) REUTERS/Arnd Wiegmann

Image used for illustrative purpose. A worker stands beside mobile maschinery during the installation of the railway tracks in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

A worker uses a measuring gauge during the installation of the railway tracks in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

An engineer sits on the special train 'Helvetia' in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. The train, which is 481 metres (1578 ft) long and weighs 787 tons, is constructed to produce concrete for the installation of the railway tracks in the tunnel. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

A worker uses a hammer during the installation of the railway tracks in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

An Austrian and a German national flag fly on mobile machinery during the installation of the railway tracks in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann

Image used for illustrative purpose. A worker places parts during the installation of the railway tracks in the NEAT Gotthard Base tunnel near Faido May 12, 2014. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles).

Image used for illustrative purpose. A worker receives instructions from an engineer during the installation of the railway tracks in the NEAT Gotthard Base tunnel near Erstfeld May 7, 2012. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles) REUTERS/Arnd Wiegmann