Immersed tunnel vs. bored tunnel
While the comparison between the immersed tunnel and the bridge alternatives –the suspension bridge being less favourable than the cable-stayed bridge –did not reveal any new findings, the bored tunnel alternative was further investigated.
Based on technical, financial and environmental data, the direct comparison between both tunnel alternatives still confirmed the priority of the immersed tunnel:
- While the construction of the bored tunnel would require a larger construction siteon Fehmarn, its effects on Lolland would be less severe compared to those of the immersed tunnel. It would also avoid a direct impact on the Fehmarnbelt’s marine environment. However, the immersed tunnel’s impact would be predominantly temporary in that it would be confined to the construction phase.
- The overall technical challenge associated with the construction of a bored tunnel is much higher than for an immersed tunnel. On one hand, the dredging and immersion process for the immersed tunnel relies on proven technology that would almost not be affected by the complex geological conditions of the Fehmarnbelt. On the other, these same conditions would pose a significant challenge to the tunnel boring machines, and it would be necessary to construct the world’s absolutetly biggest boring machines.
- The estimated construction costs for the immersed tunnel are EUR 5.5 billion, while the bored tunnel would cost EUR 6.8 billion. It would not only take a bitlonger to construct the bored tunnel (8 years compared to 6.5 years for the immersed tunnel) but also the financing would prove longer to repay, which would effectively render the project uneconomical.