Authorities in Schleswig-Holstein have officially approved the German part of the Femern link so work can now start on constructing a rail and road tunnel between Germany and Denmark.
It will be an immersed tunnel - the longest in the world of this type - with the sections constructed at a new production site with dry docks on the Danish side and they will then towed out by tug and lowered into a trench across the sea bed that will be up to 60 metres wide and 16 metres deep.
This is an amazing engineering project - the largest undertaken in Denmark - and I would recommend watching the video animation on the Femern A/S site to see how the sections of tunnel will be made and taken out to the trench.
This is also, of course, a major design project that requires expertise in road planning and for the design of infrastructure at each end and there will be an important design project for the operation stage for signage, marketing, branding and so on.
With completion planned for 2028, the tunnel will be 18 kilometres long and will link Puttgarden on the German island of Fehmarn to Rødbyhavn, on the south coast of the Danish island of Lolland, and the journey through the tunnel will take 10 minutes in a car and 7 minutes for the train.
Many make the trip across now by using the regular ferry service but for heavy freight traffic - now taken up through Jylland/Jutland and across the bridges linking to Fyn and then on to Sjælland - the tunnel will shorten the journey by 160 kilometres.
This may mean more tourists will arrive in Copenhagen by car but the real impact will be for commercial traffic and therefore, of course, for the development of the region of eastern Denmark and the south part of Sweden.
Already on the agenda is the construction of a new metro line to Malmö to run through a tunnel parallel to the Øresund bridge. For anyone commuting between the two cities, this would not make journey time shorter than the current rail journey over the bridge but the new Femern link between Germany and Denmark will mean many more freight trains crossing to and from Sweden so a metro link would relieve some of the pressure on the bridge and planners and governments are also considering a fixed link further north up the sound between Helsingør on the Danish side and Helsingborg in Sweden.