Adif completes 4.7 km T4 tunnel

Adif said on May 20 it had completed the track works on the rail connection between Madrid Chamartín station and Barajas Terminal 4, advancing a long-running project intended to bring high-speed rail to the airport before 2030. Spanish media reports said the work moves the scheme into its final phase after the laying of track on the airport branch. The link is one of the most constrained rail jobs in Madrid because part of the alignment runs under active airport infrastructure. (azierta.es) The project itself is not new. The Chamartín-T4 connection is an 8.8-km rail link whose underground section measures 4.7 km, according to project descriptions published by engineering and construction firms that worked on the original airport access. (azierta.es) Those descriptions say the line was designed with multigauge capability so commuter and high-speed trains could use the corridor. ### Why does a track milestone matter if the tunnel has existed for years? The May 20 announcement concerns the completion of track works, not the first excavation of the tunnel itself. Earlier project material from Azvi and Azierta shows the underground section and associated stations were built in the 2007-2011 period as part of the original rail access to Terminal 4. (larazon.es) What is new is the adaptation of that corridor for the airport's future AVE service from Chamartín. That distinction matters because the current phase is about fitting the route for the service Adif and transport authorities now want to run. (azierta.es) The existing infrastructure was conceived as a mixed system, with a three-rail arrangement and power systems intended to accommodate both Iberian-gauge commuter traffic and standard-gauge high-speed operations, according to the published project descriptions. ### What exactly makes the Barajas section difficult? Barajas airport is the constraint. The underground section passes beneath the airport environment, including runway areas, which limits access, construction windows and acceptable disruption. (azierta.es) Spanish media reports on the latest works described the package as part of a complex interface between rail construction and live airport operations. The 4.7-km underground stretch was built using more than one construction method. Azvi says 2.9 km was excavated as mined tunnel and 1.8 km was executed as cut-and-cover between diaphragm walls. (azierta.es) The company says the mined section used the so-called Belgian method, also known in Madrid as the traditional method, with excavation in short advances and immediate support. ### Was this corridor always meant for both Cercanías and AVE? The original design says yes. Azierta says the tunnel system installed on the airport access included a three-rail arrangement so commuter services using Iberian gauge and high-speed trains using international gauge could share a single corridor. (larazon.es) Azvi likewise describes the route as a multigauge link between Chamartín and T4. That helps explain why the latest works are being presented as a final-phase step rather than a wholly new line. The civil structure and mixed-gauge concept were already in place; the current effort is about completing the railway systems and track configuration needed for direct high-speed access. (azvi.es) ### What comes next before passengers see AVE trains at T4? Spanish media reports said the goal is to bring high-speed rail to Terminal 4 before 2030. Neither of the accessible source pages reviewed here set out a full commissioning timetable, but the reports frame the completed track works as a step toward the final delivery of the airport AVE access. (azierta.es) The next visible milestones are likely to come from Adif and Spain's transport ministry as they complete the remaining systems, testing and service-readiness work required to open the Chamartín-T4 high-speed connection. (azierta.es) The route's published specifications include mixed-gauge track, dual-voltage electrification and tunnel safety systems, all of which point to additional integration work before operations begin. (merca2.es)