Fehmarnbelt Crossing promoter Femern yesterday confirmed it would recommend the tunnelled option over the bridge proposal, despite recently lauding the benefits of the latter.
It said that an immersed tunnel would entail fewer risks in both the construction and operational phases than a cable-stayed bridge, despite the bridge being called “iconic” by the firm.
The technical risks of executing the two projects - surrounding environmental impact, navigation safety and construction cost - were the key factors in opting for the tunnel. But the decision remains provisional pending an Environmental Impact Assessment (EIA).
A final political decision on which of the two will be selected will be made in early 2011. It is anticipated that the preferred solution will form the basis for the project application to be submitted to the German authorities.
A specially enacted construction act will then be formed in Denmark and subject to approval by the German authorities.
Contracts for the construction work are not expected to be signed until 2014. It will be up to the contracting firms to organise the work, including the location of the large production sites for manufacturing bridge or tunnel components.
Femern said it had assumed that a large proportion of the steel structures for a bridge would be constructed in the Far East (possibly China) while tunnel components would be produced locally owing to their great weight. On account of the risks entailed by sea transportation of such large components, Femern said that production of concrete components should ideally be sited up to 120km from the route corridor. A more distant siting may also be considered if the contracting firms conclude that this would be more financially competitive overall.
A cable-stayed bridge across the Fehmarnbelt, with two free spans of 724m each, would be the largest spans ever constructed for either road or rail traffic. Compounded by the high shipping traffic in the area, this would pose significant risks in the construction phase in terms of cost overruns, delays and industrial accidents.
An immersed tunnel will also present considerable technical challenges during the construction phase, as a result of the intensive shipping traffic in the Fehmarnbelt. However, unlike a bridge, an immersed tunnel will not entail as many technical operations which push the limits of what has been done before. Essentially, the procedure will be the same as it was for construction of the Øresund Fixed Link’s immersed tunnel under the Drogden Channel, only many more times over and at far greater depths, such as up to 30m to 40m in the Fehmarnbelt against approximately 10m in the Øresund. The Fehmarnbelt tunnel will be just under 18km long, while the Øresund Tunnel is around 4 km long.
Both a cable-stayed bridge and an immersed tunnel would impact the marine environment in the Fehmarnbelt. The preliminary conclusion is that a bridge would have slightly more significant permanent environmental impacts than an immersed tunnel. However, the nature of these impacts does not, from a purely environmental perspective, preclude a bridge.
A number of the environmental impacts of a fixed link would be on Natura 2000 sites. In such instances, EU legislation prescribes that the least intrusive alternative must be selected.
In the interests of navigation safety, a tunnel clearly poses fewer risks than a bridge. The Fehmarnbelt is a heavily trafficked stretch of water with 47,000 vessel transits per annum (2006), including many tank vessels. In the coming years, shipping traffic in the Fehmarnbelt is expected to increase substantially to approximately 90,000 vessel transits in 2030.
However, risk analyses for a bridge show that, from a vessel perspective, navigation safety would be improved in relation to a situation with no bridge and continued ferry crossings. This would require a cable-stayed bridge with two navigational spans of at least 724m each, and the implementation of permanent, radar-based vessel monitoring in the form of a Vessel Traffic Service (VTS) system covering a range from the south end of the Great Belt to the Cadet Channel.
In financial terms, there is very little difference between the two projects. The construction estimate (2008 price level) for an immersed tunnel is €5.1bn (£4.27bn) and for a cable-stayed bridge £4.35bn.
But assessment of the overall cost of each of the two projectswould take into account the construction time and the cost of operation and maintenance. The construction time for the tunnel is estimated at six and a half years, and for the bridge, six years. The cost of operation and maintenance is slightly higher for a tunnel than for a bridge.
The payback time for the two projects would be essentially the sam - approximately 30 years for the coast-to-coast project. This means that, from an overall financial perspective, there is no difference between bridge and tunnel.