The old tunnel is nowadays used as an emergency exit and since July 2011, also as a lane used by trucks which carry flammable or other types of hazardous loads.
[1] Before the 20th century, the Aran valley was not easily accessible from the rest of Spain, especially during the winter snow season, when the Vielha mountain pass, at a height of 2,450 m above sea level, was frequently closed by snowfall.
Construction finally started in 1926 and lasted 22 years, including the Spanish Civil War period from 1936 to 1939.
Curved concrete walls were built at both ends to avoid excessive air flow.
[3] Construction of the new tunnel began in January 2002 and the work was temporarily stopped in winter 2005–2006 because the project had to be adjusted due to new safety laws.