The section Armiñón - La Puebla de Arganzón is part of the high speed line MADRID-PAÍS VASCO/FRENCH BORDER. It’s an electrified double-track high speed line (300-350 Km/h), with international gauge, for passengers and freights transportation. It has a total length of 7.5 Km, 3.4 Km out of them running in tunnel.
The section Armiñón – La Puebla de Arganzón runs through an undulating terrain that requires the construction of a 3,412 meters long tunnel to save the San Formerio’s Mountain. The presence of an aquifer at the same level of the projected tunnel, entails the construction of a singular section for the tunnel with a reinforced coating and circular in shape, in order to achieve the sealing of the section. On the other hand, the construction of three viaducts of 31, 65 and 320 meters long is also necessary, as well as three underpasses and two overpasses for the rural roads replacement.