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This train line is part of a wider transport corridor between the Black Sea and the Mediterranean.; This train line is part of a wider transport corridor between the Black Sea and the Mediterranean.;

Modernisation of Samsun – Kalin Railway, Samsun - Sivas

Samsun-Kalin rail line upgrade strengthens Türkiye's Black Sea to Mediterranean transport link

Strengthening a country’s railway connectivity can speed up journey times and improve reliability across the transport network, helping drive sustainable economic growth – but how do you upgrade existing infrastructure in a speedy, cost-efficient manner?

Türkiye's Samsun-Kalın railway line, which links the port of Samsun to Kalın in Anatolia, has been comprehensively overhauled so local residents can benefit from upgraded service standards that will significantly increase passenger and freight capacity and confort while cutting down travel times.


The modernisation of this heritage railway, one of the first built by the Republic of Türkiye, comprises the entire 378 km-long stretch of single-track, non-electrified line, and will allow for faster – and heavier – trains on the track. Average train speeds will increase as a result, significantly reducing overall travel times by about 50% down to 5 hours from an initial estimate of about 9 hours.


As a bridge between East and West, Türkiye's railway infrastructure plays a strategically important role for Europe, Asia and the Middle East. This train line is part of a wider transport corridor between the Black Sea and the Mediterranean through Kalın, and is among a series of initiatives backed by the EU to link Türkiye with the European railway network.

Arup was appointed by a Joint Venture including Çelikler-Gülermak-AZD to provide multidisciplinary engineering for both the preliminary and detailed construction design among others.

Project Summary

50% reduction in journey times (from 9h to 5h)

90%increase in rail passenger traffic

54trainsper day total capacity vs 21 prevoiusly

Planning for the future: upgrading a historical railway connection

The Samsun–Kalın railway was completed in 1932 as an unelectrified, unsignalled, standard gauge single-track line. Before the modernisation works, the outdated infrastructure meant the route was subject to frequent, costly maintenance with flooding and railway track settlements causing derailments.


Arup has provided multidisciplinary engineering design services for both the preliminary and detailed construction design, including civil engineering, geotechnics, structures and bridge assessment and strengthening, restoration of historical bridges, permanent way/track, drainage, tunnelling, as well as Traffic Control Center Building (architectural, structural, mechanical and electrical) design services.

Digital tools help optimise the design process

Upgrading an existing rail link throws up significant challenges. Cutting through the Pontic mountains, the line’s geographic conditions rendered the topographic site surveys difficult, while the high gradients and tight curves of the line itself made soil investigation and improvement works similarly challenging.


The assessment and strengthening of historical protected bridges was a key aspect of the project. The work includes 38 new bridges, as well as infrastructure and superstructure upgrade works on 41 historical bridges that have been assessed for increased axle load and combined seismic events.

The 3D point cloud scanning of existing historical bridges and for some tunnels provided highly accurate data sets, which allowed the project to progress seamlessly to the next phases. The whole project was designed in less than 36 months, with works underway simultaneously across the line, allowing for a speedier project delivery that helped keep budget under control.

Our multi-disciplinary approach to problem-solving means our engineers have managed to solve the many challenges involved in upgrading existing railway infrastructure like historical bridges and tunnels in a speedy, cost-effective manner while preserving it’s historic value. ” Ali Sengoz Ali Sengoz Associate Director

The historical design constraints of the existing infrastructure also made remediation and upgrade works a complex task. The historical tunnel’s steam-era cross section had to be adjusted to accommodate changes to the superstructure including increasing loading gauges, as well as securing the height clearance required to fit electric installations.

With 47 tunnels including 8 avalanche tunnels, the line includes about 7,790 m of tunnels throughout, with the longest tunnel alone measuring 586 m.

Other structure upgrades in the project include the retrofitting of 29 station and stabling yards to make them universally accessible to pedestrians including under- and overpasses. In addition, a total of 1,253 hydraulic structures were designed for this project, a key element for this region that receives heavy rainfall throughout the year.

Taken together, all these different measures have
significantly increased the line’s daily capacity to 54 train journeys from around 21 before, allowing for better transport flows and resulting in fewer delays.

The infrastructure upgrade was 80% funded by the European Union, one of the largest projects ever sponsored in terms of budget outside the EU. The project had a complex structure in terms of funding and contractors, so optimal stakeholder management was vital. The operator, Turkish State Railways, is looking to serve the public, fulfilling the country’s ambition for a modern railway network.