Yellow Line metro extension - Future - proofing Stockholm’s transport network

The Yellow Line is one of Sweden’s most ambitious infrastructure investments - a transformative metro extension designed to support Stockholm’s long-term goals for sustainable growth, improved connectivity, and urban resilience.

Connecting Fridhemsplan in central Stockholm to Älvsjö in the south, the new line will add over 8 km of twin tunnels and six new underground stations to the city’s expanding metro network. The fully automated, driverless line is expected to serve up to 75,000 passengers daily and unlock development for tens of thousands of homes.

Mikael Thorsell, Project Manager for Ramboll, says, “This isn’t just about building a metro - it’s about delivering a foundation for future growth in one of Europe’s most dynamic capital regions. The scale, the collaboration, and the urban impact make it a standout reference for us.”

Ramboll, in a joint venture with TYPSA, is responsible for the design and engineering of two major packages (BH1 and BH3). The scope includes:

• Detailed design of tunnels and underground stations, including rock mechanics, concrete structures, and fire safety systems
• Drainage and dewatering systems tailored to dense urban conditions
• Track and depot design for fully automated GoA4 operations
• Model-based documentation and digital coordination across disciplines
• Contract packaging and delivery planning for both AB04 and design-build phases

The Yellow Line is one of the few metro projects in Sweden to use tunnel boring machines (TBMs) - chosen to reduce disruption in dense urban areas while addressing complex spatial and geotechnical challenges. The project’s technical scope also includes multi-phase planning, model-based documentation, and coordination across several contract formats.

Crucially, it also supports Stockholm’s long-term carbon and climate goals. The design targets a 50% reduction in lifecycle emissions, achieved through early-stage carbon modelling, material-efficient structures, and integrated resilience measures including tunnel waterproofing and flood protection.

Beyond its engineering complexity, the Yellow Line supports Stockholm’s broader urban and social ambitions. It improves mobility across underserved districts, enhances labour market access, and eases pressure on existing transport infrastructure. By enabling high-capacity, low-emission travel, the project makes a long-term contribution to inclusive urban development and regional connectivity.

It also positions Stockholm’s metro system to meet future demands - both in terms of population growth and climate resilience - setting a new benchmark for next-generation public transport infrastructure.

The Yellow Line stands as a powerful example of how infrastructure can deliver on multiple fronts: scale, sustainability, and long-term social impact. It reflects what’s possible when urban transport is treated not just as a system but as a catalyst for shaping the future of cities.