THE TUNNEL The tunnel is a a passageway through or under something, usually underground. Before cars and trains, the tunnels carried only water. These were created by the Roman engineers. Today, the mountain or the ocean is not an obstacle for a tunnel. The tunnel boring machines can be used to automate the entire tunneling process. The biggest tunnel boring machine built was operated to drill the tunnel as part of the High Speed Raillink South in the Netherlands. Its diameter is 14.85 m.

Tunnel boring machine

LONGEST TUNNELS The longest rail tunnel in the world is Seikan Tunnel, at 53.9 km (33.4 miles), of which 23.3 km (14.5 miles) is under the sea. The longest road tunnel in the world is Laerdal Tunnel in Norway at 24.5 km (15.2 miles).

Laerdal Tunnel, Norway

OUR FAVORITE Our favorite tunnel is The Channel Tunnel. The Channel Tunnel is the second-longest rail tunnel in the world, with a total length of 50 km (31 miles), of which 39 km (24 miles) is under the sea. The Channel Tunnel connect France and England and consists of three parallel tunnels: two rail tunnels and one service tunnel between them. Digging the tunnel beneath the English Channel took 15,000 workers over seven years; it was completed in 1994. The Channel Tunnel is operated by Eurotunell.

The Channel Tunnel