Environmental and safety arguments favour an immersed tunnel

The recommendation was based on a number of investigations into the environment, soil conditions and navigational safety. Technical surveys of different solutions for both a bridge and a tunnel were also carried out.

In the treaty between Germany and Denmark of September 2008, the preferred technical solution was a cable-stayed bridge with an immersed tunnel as the preferred alternative.

New, thorough studies
This was based on a feasibility study from 1999 which also revealed that other alternatives such as a bored tunnel and a suspension bridge would involve a number of technical and environmental problems.

On this basis, Femern A/S, in the spring of 2009, asked two groups of consultants to prepare conceptual designs for an immersed tunnel and a cable-stayed bridge.

Following the completion of the conceptual designs, Femern A/S, in November 2010, resolved that an immersed tunnel would involve fewer risks than a cable-stayed bridge during both the construction and operational phases.

The evaluation attached particular importance to the environment, navigational safety, technical risks and the project’s economy.

The environment
One important parameter in the choice of technical solution was the project’s impact on the environment.

A cable-stayed bridge and an immersed tunnel will both impact on the Fehmarnbelt environment. The current view is that a bridge would have a slightly greater and more lasting environmental impact than an immersed tunnel although not to an extent that, from an environmental perspective, would exclude a bridge solution.

A number of the environmental effects that a fixed link would bring about would impact on Natura 2000 areas. In such cases, EU legislation stipulates that the least intrusive solution must be chosen.

Navigational safety
From the perspective of navigational safety, it is clear that a tunnel would involve fewer risks than a bridge. With 47.000 ship passages per year (2006), including a large number of tankers, the Fehmarnbelt is already very busy. Moreover, it is expected that the volume of shipping will increase significantly over the years ahead - to around 90.000 passages by 2030.

The risk analysis for a bridge, however, also shows that, from a shipping perspective, navigational safety can be improved compared to a scenario with no bridge and with continuing ferry services. This assumes the construction of a cable-stayed bridge with two passage spans of at least 724 m and the installation of a permanent radar-based vessel monitoring system in the form of a VTS system (Vessel Traffic Service), covering the area from southern Storebælt to Kadetrenden.

Technical risks
A cable-stayed bridge across the Fehmarnbelt with two free spans of 724 m each would be the largest structure ever built for road and rail traffic. Together with heavy shipping traffic in the area, this would involve significant risks during the construction phase in terms of increased costs, delays and work-related accidents.

An immersed tunnel would also be a significant engineering challenge during the construction phase, e.g. as a result of the high volume of shipping in the Fehmarnbelt. An immersed tunnel, however, would not present as many extreme engineering challenges as a bridge.

Finance
Financially, there is little difference between the two projects. The conceptual designs from 2010 estimate the cost of an immersed tunnel to be approx. DKK 37.9 billion and DKK 38.5 billion for a bridge (2008 prices).

A general estimate of the financial implications of the two projects must include construction time and operational and maintenance costs. The construction period for the tunnel is estimated at six and a half years and atsix years for a bridge. Operational and maintenance costs are somewhat higher for a tunnel than a bridge.

By and large, the repayment period for the two projects is identical. This implies that from an economic perspective, the projects should be assumed to be equal.