The tunnel, which forms part of an expansion to the country's 300km West Coast Line between Gothenburg and Lund, will run under the coastal town of Varberg. It will accommodate the West Coast Line's expansion to a double-track railway, which will increase capacity and reduce travel times for passenger and freight services.
Atkins - alongside a number of other consultants - has already completed the phase 1 design of the project, which included the development of the implementation plan.
The next stage involves detailed planning for the construction phase of the new tunnel under a time and materials contract worth an initial £13m.
The expansion of the railway has been under way since 2015 and approximately 85% of the line has been upgraded. The project, which is being led by the Swedish Transport Administration and Swiss construction company Implenia, is expected to be completed in 2025.
Atkins Sweden CEO Johannes Erlandsson said: “The Varberg tunnel and the line expansion will benefit the entire west coast of Sweden by connecting towns, cities, businesses and communities. Having been involved since its early stages, we now look forward to working with our partners to deliver this complex and transformative project.”