The longest tunnels ever constructed in Spain are located in the Sierra of Guadarrama with a length of over 28 km and they represent an unprecedented project in this country. The expansion of the high-speed railway network in Europe, in particular in Spain, is causing an increase in the number of tunnels and in their length. As a consequence of the serious accidents in recent years, there has been growing concern about the safety of railway users, this has become one of the main considerations in the functional design of tunnels.