With the improvement of construction techniques and urban development, tunnels are now built under our cities.

That means mainly lack of surface place which is now the case not only in mega cities but in nearly all town and cities around the world.

Since the end of the 19th century underground tunnels have been used for mass transit transportation in the cities.

The most well known network of pedestrian tunnels has been developed by the city of Montreal. This underground network has been created to allow inhabitants to circulate in the city during the winter.

Another use of the underground space in cities can be the transport of goods getting in and out of the city.

Increased traffic in cities during the last decades has caused a quick congestion of surface parking. Therefore, new solutions were required.

Underground railway stations or mass transit stations are of the most importance as they are the main part of underground structures seen by the public.

Interurban road tunnels have been built for centuries to enable vehicles crossing mountains and topographical accidents.

Railway tunnels are nearly as old as railways. The first one was built in 1826 on the line between Liverpool and Manchester. Later on, the development of railways in the late 1880's led to a dramatic development of railway tunnels.

As navigation canals have to be built as horizontal as possible, as soon as topographical accidents appear the construction of tunnels is needed.

Some other structures need the construction of tunnels. For instance, tunnels have been built on ski resorts such the ones built in Tignes.