The 675-meter Castellana tunnel, now nearing completion beneath one of Madrid’s basic thoroughfares, is poised to become a benchmark for smart urban infrastructure. Excavation is finished, and daylight is visible at both ends of the tunnel. The project remains on track to open to traffic in December 2026, as scheduled by the city council.
The roadworks form part of a broader surface redevelopment between calle Sinesio Delgado and the Nudo Norte of the M-30. The landscaped corridor is approximately 90 meters wide and will create about 70,000 square meters of public space above the tunnel. Reporting by El Debate on October 20 described the project as entering its final phase, with the pergola taking shape and solar panels expected to be installed next.
Unlike previous projects, the Castellana tunnel is designed with two levels to minimize disruption to existing trees and preserve as much green space as possible. The basic section will have three lanes in each direction, alongside additional access points and exits. A future extension is planned to connect the tunnel with Madrid Nuevo Norte and the Begoña neighborhood, further linking the city’s transport network.
AI-Powered Traffic Management
The tunnel’s technology sets it apart. It will use artificial intelligence systems to detect incidents in real time and identify vehicles. The systems will also monitor speeds and air quality. They will automatically adjust ventilation and other parameters to improve safety and efficiency, offering a impressive upgrade over older tunnels such as those beneath Madrid Río.
Information from 20 Minutos, the AI will also analyze traffic patterns and emissions, allowing dynamic management of the underground roadway. The approach is expected to reduce congestion and improve response times to incidents, while supporting the city’s environmental goals.
Madrid is also completing a separate underground-road project on the A-5. Telemadrid has reported that excavation and civil works there are complete, with crews installing ventilation and lighting ahead of a connection to the M-30 expected between November and December 2026. The A-5 tunnel is about three kilometers long, with three lanes in each direction. Those specifications apply to that project, not the shorter Castellana tunnel.
Transforming Urban Space
Above ground, the Castellana project is reshaping the area with gardens and a large fountain, while pergolas are also taking shape. The roughly 70,000-square-meter public space is intended to connect La Paz hospital, the city’s five towers, the historic San Cristóbal neighborhood, and the future Madrid Nuevo Norte business district. Once the tunnel opens, only public transport and local traffic will use the surface roads, freeing up space for pedestrians and green areas.
The redevelopment is intended to create a more continuous public-space link across land previously dominated by traffic. The Castellana tunnel is also intended to anchor the northern end of the city’s basic north-south axis, reinforcing Madrid’s urban structure and supporting future development in the area.
Context and Outlook
Madrid’s investment in underground roads paired with surface parks reflects a wider effort to combine transport infrastructure with public-space improvements. For comparison, the A-5 project is expected to provide about 80,000 square meters of parks and gardens, according to remarks by Madrid mobility delegate Borja Carabante reported by Europa Press. The schemes are separate, but both show the city’s approach: moving major traffic corridors underground while reclaiming the space above.
AI is expected to become more common in traffic management as cities seek to balance growth with environmental and quality-of-life concerns. If the Castellana tunnel meets its aims, it could become a model for similar projects across Spain and beyond.
