Ambitious Railway Tunnel Beneath Vienna Reaches Pivotal Milestone
Vienna is no stranger to ambitious infrastructure projects, but few rival the sheer scale and strategic significance of the U2xU5 metro expansion. Heralded as the city’s most substantial climate protection initiative, this megaproject aims to transform urban mobility while slashing emissions. At the heart of this transformation is the southern extension of the U2 line, and it has just hit a major milestone: the successful completion of tunnel boring on Track 2.
This underground breakthrough, achieved at the Augustinplatz emergency exit, marks the halfway point of a meticulously coordinated project helmed by the STRABAG and PORR consortium. With one of the two parallel tunnels now in place, Vienna inches closer to a cleaner, faster, and more connected future.
A Machine Named Debohra
The driving force behind this engineering feat is a colossal tunnel boring machine (TBM) affectionately dubbed Debohra. Designed specifically for Vienna’s subterranean geology, Debohra stretches an impressive 127 metres and weighs in at 1,300 tonnes. She was built in Schwanau, Germany, by Herrenknecht and assembled from over 27,000 individual parts before being shipped in pieces to the Austrian capital.
After reassembly at Matzleinsdorfer Platz earlier this year, Debohra was lowered into position and fired up in the autumn. Since then, she has been carving her way through the dense Wiener Tegel earth using a technique reminiscent of keyhole surgery. Working almost invisibly beneath the surface, she has completed a roughly 2-kilometre stretch of tunnel connecting Matzleinsdorfer Platz to Augustinplatz.
What makes Debohra’s journey even more remarkable is the sustainability baked into the operation. Instead of hauling excavated earth by lorry through busy streets, material was extracted via a central shaft and removed offsite. This clever approach has saved an estimated 20,000 truck trips and prevented around 75 tonnes of CO2 from entering the atmosphere.
Engineering at its Finest
The project is being spearheaded by ARGE U2/17-21, a joint venture between construction giants STRABAG and PORR. For Gerhard Urschitz, Head of Tunnel Construction at STRABAG, the breakthrough is a testament to teamwork and precision: “A breakthrough always marks a critical turning point in tunnel construction – especially for a complex urban project like this one. It’s symbolic of what can be achieved when forces unite to create sustainable infrastructure that genuinely enhances city mobility. We’re immensely proud of this success – it’s teamwork at the highest level.”
PORR CEO Karl-Heinz Strauss echoed this sentiment, emphasising the importance of collaboration: “Milestones like this are only possible when everyone involved works with passion, precision, and in close alignment. The breakthrough at Augustinplatz shows how strong our partnership within the ARGE is – and what we can accomplish for the future of urban mobility. The U2xU5 expansion carries great responsibility, and we’re committed to it with full conviction.”
What Comes Next
With the first tunnel complete, attention now shifts to the second tube. This will involve partially disassembling Debohra and transporting the components back to Matzleinsdorfer Platz. Meanwhile, the trailing elements of the TBM will be pulled backwards through the completed tunnel, allowing for reassembly and another round of cutting through Vienna’s underground.
The twin tunnels will connect four brand-new U2 stations: Matzleinsdorfer Platz, Reinprechtsdorfer Straße, Pilgramgasse, and Neubaugasse. Each stop will play a crucial role in improving accessibility, shortening journey times, and reducing reliance on cars within the Austrian capital.
This phase of the build is due to continue through late 2025, by which time both tunnels should be ready for outfitting with the necessary infrastructure: tracks, ventilation, emergency exits, and digital signalling systems.
Meet the Giants Behind the Project
STRABAG SE is one of Europe’s most formidable players in the construction sector, renowned for its innovative strength and financial stability. With around 86,000 employees and an annual output of roughly €19 billion, STRABAG operates across the full value chain of the construction industry – from concept and design to operation, reuse, or even demolition. The firm is engaged in over 250 innovation and 400 sustainability projects, demonstrating its commitment to future-proofing the built environment.
PORR AG, meanwhile, brings 150 years of experience to the table. As one of Austria’s top construction groups, with 21,000 employees and revenues of €6.7 billion in 2024, PORR is active not just in its home country but across Germany, Switzerland, Poland, the Czech Republic, Slovakia, and Romania. It also delivers high-impact projects in select global markets, including Norway, the UK, and Qatar. The company’s shares are traded on the Vienna Stock Exchange.
Together, STRABAG and PORR embody what it means to build responsibly and ambitiously, aligning cutting-edge construction with climate-conscious methodologies.
A Model for Urban Transport Infrastructure
Beyond Vienna, the U2xU5 project is drawing international attention. It sets a powerful precedent for how cities can tackle mobility challenges while staying firmly aligned with environmental goals. By combining tunnel boring technologies, digital monitoring, emissions reduction, and multi-stakeholder collaboration, this initiative is a prime example of best practice in urban infrastructure development.
The city is also reaping economic benefits. Large infrastructure projects like this stimulate local employment, attract global engineering talent, and future-proof the region for growth in housing, commerce, and tourism.
Vienna’s Next Chapter
With one tunnel behind and another just beginning, Vienna’s journey toward a smarter, cleaner transport network is gaining traction. The U2xU5 expansion is not just about digging tunnels. It’s about building connections – between communities, careers, and a carbon-neutral tomorrow.
The collaborative energy driving the project is palpable. With every metre excavated, Vienna edges closer to a reality where hopping on the U-Bahn means leaving a lighter footprint. And that, in today’s climate-conscious world, is a journey worth celebrating.
