The tunnel under the Estuary, the most significant infrastructure project to be built in Bizkaia over the next five years, has just cleared its final administrative hurdle before construction begins. The Provincial Council has awarded two of the four contracts into which the project will be divided due to its high complexity.

Work is set to commence this summer on the Right Bank, focusing on the Artaza entrance and the gallery that will extend from the roundabout to the Lamiako plain. Both phases of work are projected to last 60 months – five years – and will require a combined investment of 277 million euros, plus VAT.

The Artaza entrance will be executed by the UTE comprising Ferrovial, Construcciones Mariezcurrena, and Cycasa, while the section of the subfluvial tunnel reaching the Estuary will be undertaken by Nortúnel, Geotunel, and Tunelan. Future contracts will be awarded for the Left Bank, including the Ballonti access and the tunnel connecting Portugalete and Lamiako, which involves drilling beneath the riverbed. Initial estimates place the total cost at around 540 million euros.

Nearly 30 years have passed since the first discussions about finding an alternative to connect the two banks of the Estuary and alleviate congestion on Rontegi, which currently handles 175,000 vehicles daily and is by far the most congested road in Bizkaia. The subfluvial tunnel is expected to divert 74,000 cars, easing traffic in the area, La Avanzada, and the A-8.

Construction will begin at the Artaza junction, identified as one of the project's most sensitive areas. This location has the highest density of housing and public facilities, including a school and a high school, and is where machinery must first reach the Lamiako plain. This operation will involve over 80 micro-blasts and the excavation of a significant portion of the Artaza park, situated between Leioa and Getxo. Due to the proximity of residential areas, the Provincial Council has decided that open-air work will be conducted during office hours, while drilling within the gallery will proceed 24 hours a day.

The tunnel under the Estuary will span 3.2 kilometers and consist of two distinct 'tubes,' one for each direction of traffic. The construction challenge is considerable because, in addition to the constraints at Artaza, it must navigate the sandy area of Lamiako and drill 45 meters below the riverbed. The Ballonti access is, a priori, the least problematic, which is why its construction will start later. The aim is to synchronize the completion of all sections.

The Provincial Council's current forecast suggests the subfluvial tunnel could be completed around 2032. In global terms, the tunnel's construction will involve excavating 1.8 million cubic meters of earth and using 21,235 tons of steel. Daily, 170 trucks will remove excavated material from the subfluvial site, with 90 from the Artaza entrance and 80 from Ballonti. This material will be transported to the facilities of the Port of Bilbao, where it will be used for dike infill.