Sunday, August 10, 2008

Øresund Link

The ambitious project to construct a fixed rail and road link across the 65-mile (105-kilometer) Øresund Strait was agreed to by the Danish and Swedish governments in March 1991. The resulting 10-mile (16-kilometer) combination of submarine tunnel, artificial island, and bridge, carrying a double-track electrified railroad and four lanes of freeway between Kastrup, Denmark, and Lernacken, Sweden, was officially opened on 1 July 2000. Responding to complex social, cultural, economic, ecological, geological, and technological constraints, the transoceanic international highway is a major achievement of design and logistical skill, demonstrating that high technology and environmental sustainability are compatible.

Each country was responsible for extending its transport system to connect with the link. A/S Øresund built the Danish land works, while Svensk-Danska Broförbindelsen constructed those in Sweden. The government-backed companies continue to be equal partners in the Øresund Consortium, initially charged with financing and building the link. Since completion, the consortium owns and operates it, funded by tolls charged to cover maintenance costs and to finance loan repayments.

It is reasonable to describe the link in a logical way, crossing from west to east. The Danish land works include about 11 miles (18 kilometers) of railroad from Copenhagen Central Station to the coast and 2.5 miles (4 kilometers) of track exclusively for freight trains. Work was completed in fall 1998, about a year after the Danish freeway system was extended to run beside the railroad. Where it passes through built-up areas, the wide transportation corridor is 23 feet (7 meters) below grade to reduce noise; it is even roofed over in places. Extensive planting—over 350,000 trees and shrubs—makes it less visually intrusive while dampening the traffic noise.

The coast-to-coast link begins with a 470-yard-long (430-meter) artificial peninsula at Kastrup on the Danish shore, built of dredged material from the Øresund seabed. It is the site of the entrance/exit of the 2.5-mile-long (4-kilometer) tunnel that joins Kastrup and an artificial island (also built of dredged material) across the Drogden Channel. The tunnel, the longest immersed tube for both road and rail in the world, is constructed from twenty prefabricated concrete elements, some weighing as much as 61,600 tons (56,000 tonnes). It contains separate well-lit, fire-resistant tubes for each direction of the freeway and the railroad; that is, four in all, as well as a central gallery for maintenance access and emergency evacuation. The components were cast at Copenhagen North Harbor, floated, and towed by four tugs to the tunnel trench about 8 miles (12 kilometers) away. When each element was lowered into place and secured, the trench was refilled around it. The top of the tunnel is about 35 feet (11 meters) below sea level.

Eastbound traffic emerges from the tunnel on a narrow, 2.7-mile-long (4.3-kilometer) artificial island that has been named Peberholm, over which the open highway and the railroad make the transition to the spectacular 4.9-mile-long (7.85-kilometer) Øresund Bridge, which gracefully curves across the sea, soaring to a clear height of 186 feet (57 meters) above the Flintrännan navigation channel between the Strait of Kattegatt and the Baltic. The two-level—freeway above, railroad below—cable-stayed High Bridge is supported by four pylon legs. It is 3,570 feet (1,092 meters) long, with a 1,600-foot (490-meter) main span. The High Bridge is connected to Peberholm Island and the Swedish coast by approach bridges, 2.34 and 1.88 miles (3.74 and 3.01 kilometers) long, respectively, carried on a total of 51 reinforced concrete piers. Many of the bridge components—caissons, piers, road decks, and superstructure—were fabricated in Karlskrona and Malmö, Sweden, others in Cadiz, Spain. They were lifted into place by the 9,500-ton capacity (8,600-tonne) floating crane Svanen using a satellite navigation system to achieve the necessary precision.

Land works in Sweden include a 4.7-mile (7.5-kilometer) extension of the existing Continental line, connecting the Øresund Link near the coastal town of Lernacken to Malmö Central Station and beyond. That stage of the work was finished in 1999. A new 6-mile (10-kilometer) freeway links Lernacken to the Outer Ring Road east of Malmö. The 2.6-mile (4.2-kilometer) City Tunnel, scheduled for completion by 2007, is planned to connect Malmö Central with the Øresund rail link. New tracks have been built for freight traffic. Freight trains are limited to speeds of 75 mph (120 kph), but the track is designed for highspeed passenger trains traveling at 125 mph (200 kph). The 34-mile (55-kilometer) international commuter journey between Sweden and Denmark takes just 30 minutes.

Environmental awareness characterized the entire project. The link was not allowed to affect water flow in Øresund, so the seabed, was partly excavated to offset the impact of the peninsula, the artificial island, and the bridge pylons. Waste from the construction works was strictly monitored, and more than 7.82 million tons (7.11 million tonnes) of spoil from boring, dredging, and digging was used to create the artificial peninsula and the island. Moreover, the work was organized to avoid disruption of natural patterns, such as the seasonal growth of seaweed, the use of wetlands by birds, and the migration of schools of herring.

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