The plaintiff is a city consisting of several districts including the island of Fehmarn. The plaintiff appeals against the expansion of the local jurisdiction of its authorities to include part of the fixed link to Denmark across the Fehmarn Belt. According to the Treaty between the Federal Republic of Germany and the Kingdom of Denmark on a fixed link across the Fehmarn Belt dated 3 September 2008 (Federal Law Gazette II 2009 p 800) (the Treaty), which came into force for Germany on 14 January 2010 according to the notice dated 29 April 2010 ( BGBl II p 479), a fixed combined road and rail link is to be created between the district of Puttgarden on Fehmarn and Rødby on the Danish island of Lolland in the approximately 18 km-wide Fehmarn Belt. Article 1 of the Treaty provides that the Kingdom of Denmark will build and operate the link and will bear the costs. The contracting States are responsible for the costs of the hinterland connection for their own sovereign territories. The technical design as a bridge or tunnel remained open in the Treaty, whereby the States assumed in the Preamble that 'according to knowledge acquired so far, a cable-stayed bridge would particularly promote achievement of the common goals'.

The Treaty provides that Denmark will establish a company to undertake the tasks of preparation, planning, drafting, obtaining permits, awarding contracts, setting up, financing and operating and maintaining the link. Denmark followed suit with the establishment of Femern A/S, which is wholly owned by the Danish State. The Danish law on the creation and operation of a fixed link over the Fehmarnbelt with the associated hinterland connection in Denmark of 4 May 2015 (Lov nr 575 af 4.5.2015 om anlæg og drift af en fast forbindelse over Femern Bælt med tilhørende landanlæg i Danmark - anlægslov, available at https://www.retsinformation.dk) contains numerous authorisations for the construction and operation of the link. This is now to be created in the seabed as an underwater tunnel. A two-lane railway line and a four-lane trunk road (Europastraße 47) will run through the tunnel.

The law on the expansion of administrative districts to include the fixed link across the Fehmarnbelt (District Expansion Law) of 13 February 2019 (GVOBl p 42) provides that: 'The districts of the authorities of the state, the Ostholstein district and the city of Fehmarn as well as other public administration bodies whose districts encompass the area of the state, the Ostholstein district or the city of Fehmarn, also extend to the area of the fixed link across the Fehmarn Belt, as far as it is located in the German territorial sea and in the German exclusive economic zone'. The declared aim of the law is to enable police, rescue workers, regulatory authorities and other public administration authorities to take action right from the start of the construction of the tunnel.

The plaintiff commissioned an expert to assess the efficiency of the fire services in the city of Fehmarn, taking into account the expansion of the area of responsibility to include the link. In his report of 9 September 2019, the expert concluded, among other things, that a main station with professional firefighters had to be set up under the direction of the Fehmarn volunteer fire brigade. In addition, the number of emergency services should be increased and the equipment of the fire brigade expanded. The expert also quantified the personnel costs and the costs of additional equipment likely to be required to ensure fire protection in the sea tunnel.

The plaintiff appealed to the State Constitutional Court on 5 November 2019. It was of the opinion, amongst other things, that the contested provisions violate the constitution of the State of Schleswig-Holstein on the basis that the State of Schleswig-Holstein has no sovereign powers in the exclusive economic zone (EEZ) of Germany, in which part of the planned sea tunnel is located. According to UNCLOS, which entered into force for Germany on 16 November 1994 according to the announcement of 15 May 1995 ( BGBl II p 602), the EEZ, and the continental shelf as an integral part of it, are not part of the national territory of the respective coastal State. Even if limited sovereign rights of the coastal State in this maritime zone result from UNCLOS, the Convention does not assign them to any individual federal States. There is no agreement between Schleswig-Holstein and Mecklenburg-Western Pomerania that determines who is responsible in the Baltic Sea. It is not regulated which federal State may exercise competencies in the EEZ. The Treaty would at most result in joint public law jurisdiction of the Federation and the States for matters of public safety and order.

The Treaty does not contain the necessary extension of national law to include the EEZ. The fixed link across the Fehmarn Belt is subject to the provisions of arts 56 and 60 of UNCLOS on the establishment and use of artificial islands, installations and structures. In order for national safety and regulatory law to be applied to the crossing structure, express extension clauses are required, which cannot be found either in the Treaty or in national law. Even if the Treaty regulates the responsibility of the security and regulatory authorities of Schleswig-Holstein for the area of the tunnel located in the EEZ, the legislature has, by extending the responsibilities of all authorities of the State, the Ostholstein district and the city Fehmarn to the EEZ, by far exceeded the scope of regulation allocated under international law, as this also made authorities responsible that were not entrusted with tasks of public safety and order.

The Schleswig-Holstein State government countered that the plaintiff's statements regarding the State's lack of regulatory competence for the part of the tunnel in the area of the EEZ were incorrect. It follows from art 85 of UNCLOS that the functional restrictions beyond the territorial sea should not affect the coastal State's unlimited right to build and use tunnels. Therefore, there is no need under international law to assign sovereign powers for tunnels in the area of the EEZ. In addition, the exercise of State powers according to the division of powers of the Basic Law [the German Constitution] is basically a matter for the States, which thus also have sovereign powers in the area of the German EEZ, unless, in exceptional cases, an allocation to the Federal government exists. The horizontal division of competencies between Schleswig-Holstein and Mecklenburg-Western Pomerania in the area of the EEZ is based on the principle of equidistance, from which it follows that Schleswig-Holstein is responsible.

Held: Constitutional complaint dismissed.

The Court held that the State of Schleswig-Holstein has legislative competence for the section of the fixed link across the Fehmarn Belt which lies in the German territorial sea. The same applies to the section of the link that is to be built in Germany's EEZ. Since Femern A/S will not carry out the sea crossing as a bridge, as originally intended, but as a tunnel structure, the rules on the use of the EEZ (arts 55-75 UNCLOS) are not relevant. According to art 85 UNCLOS the coastal State has exclusive competence for the construction of tunnels in the continental shelf.

The territorial sea is a strip of sea that connects to the coastline or the internal waters of a State. In principle, Germany takes the width of 12 nautical miles for its territorial sea. In the Fehmarn Belt, the distance between the German and Danish coasts, as in large parts of the western Baltic Sea, is less than 24 nautical miles. In addition, a 'High Sea Corridor' was set up, which international shipping is to use as a transit sea route. There the territorial sea is further limited by the fact that the German and Danish territorial seas leave a strip of about two nautical miles wide on either side of the centre line as a State-free body of water, which is designated as the EEZ of Germany and Denmark, respectively. (See proclamation of the Federal Republic of Germany on the establishment of an exclusive economic zone in the North Sea and the Baltic Sea of 25 November 1994, Federal Law Gazette II p 3770, with effect from 1 January 1995; Bekendtgørelse nr 584 af 24 June 1996 om Danmarks eksclusive økonomiske zone with effect from 1 July 1996, available at https://www.retsinformation.dk).

The coastal State has sovereignty over the territorial sea according to art 2.1 UNCLOS and thus full territorial sovereignty; the territorial sea is part of the national territory. Since the Basic Law does not recognise any non-Federal or Federal-direct areas, the national distribution of competences that applies to the mainland must also be related to the territorial sea. Regardless of the fact that the exact course of the State border between Schleswig-Holstein and Mecklenburg-Western Pomerania in the territorial sea is disputed due to the lack of a federal stipulation or an international treaty regulation, the area of the fixed Fehmarn Belt link in the territorial sea is subject to the local jurisdiction of the State of Schleswig-Holstein. As far as it takes into account the interests of individual federal States, the Treaty only mentions the State of Schleswig-Holstein. In the aftermath of the Treaty, the State of Mecklenburg-Western Pomerania also made it clear that it does not claim any sovereign or functional sovereignty in the area in which the tunnel will be located.

Contrary to the plaintiff's submission, the question of jurisdiction in the area of the fixed link across the Fehmarn Belt is irrelevant to the coastal State's sovereign powers in the EEZ, which are only functional under maritime law. The planned sea tunnel is a structure on the continental shelf. Article 85 UNCLOS defines an exception for tunnels in the continental shelf. This provision recognises the right to build sea tunnels under customary law. An exception provision identical to art 85 UNCLOS was already contained in art 7 of the Convention on the Continental Shelf 1958, which came into force on 10 June 1964, when the current UNCLOS classification of marine zones did not yet exist. The adoption of the untouched formula from the Convention on the Continental Shelf in the new art 85 UNCLOS would have been superfluous if sea tunnels had been placed under the regime of the EEZ when UNCLOS came into force.

The term 'exploitation' ['Ausbeutung'] in art 85 UNCLOS - the official English text speaks of 'the right of the coastal State to exploit the subsoil by means of tunneling', so that the German translation 'to use' ['zu nutzen'] is imprecise - indicates that the status of the seabed is not affected by the construction of the tunnel. Taking possession of the seabed through the construction of the tunnel does not result in an occupation in the sense of territorial title under international law. The tunnel is a structure in the continental shelf. The area in question remains part of the continental shelf and does not become the sovereign territory of the coastal State. This does not exclude, but on the contrary entails, that the coastal State exercises the necessary sovereign powers to regulate all affairs regarding the tunnel and in the tunnel in its continental shelf. These sovereign powers, which are functionally restricted to the construction and operation of the tunnel, including legislative competence, result from the right of the coastal State to construct it.

An express extension of national substantive law to the area of the fixed link across the Fehmarn Belt is not required. In the case of a marine tunnel, Article 85 UNCLOS allows the coastal State to exercise all sovereign rights required for tunnel operation under customary law. This implies that its national law applies ipso iure there, be it material security and regulatory law or organisational law, such as regulations regarding the competence of authorities.