Denmark and Germany have signed an agreement to build a 20km (12 mile) bridge between their two countries over a stretch of the Baltic Sea.
At the moment, traffic between Copenhagen and Hamburg has to use ferries to cross the Fehmarn strait.
Work on the 4.2bn euros (£3.4bn, $6.2bn) road and rail link should begin in 2012 and be finished by 2018.
However, German environmental groups and some local authorities are strongly opposed to the plan.
The bridge will stretch from Rodbyhavn, on the Danish island of Lolland, to Puttgarden on the German island of Fehmarn.

The project will be financed almost entirely by Denmark and the cost recouped through tolls. Germany will only pay for linking the bridge to its existing road and rail system.
The agreement was signed by German Transport Minister Wolfgang Tiefensee and his Danish counterpart Carina Christensen in Copenhagen on Wednesday.
"This is a good day for the strengthening of communication routes across Europe," Mr Tiefensee said.
"This is northern Europe's biggest construction project. When we expand Europe, we also have to build bridges."
A group of Germans opposed to the bridge staged a peaceful protest near where the signing took place.
Their spokesman, Juergen Boos, said the six-year construction would hurt Fehmarn's tourism industry and would be a threat to some 20 million birds along Fehmarn's coasts.

'Expensive project'
The German Nature Protection Federation has said it will exhaust all legal possibilities to try to stop the project.
Michael Cramer, a Green member of the European Parliament, said Denmark and Germany had made "a multi-billion-euro mistake".
The project "is among the most expensive single projects in the [European Union] Trans-European Networks plan and also one of the most dispensable," he said.
However, Carina Christensen dismissed the criticism saying the link would mean a reduction in greenhouse gases compared with the ferries that presently cross the strait.