Denmark and Germany now building the world's longest immersed tunnel
https://edition.cnn.com/travel/article/fehmarnbelt-longest-immersed-tunnel-cmd/index.html
It must be dramatic change for passengers moving between Copenhagen and Hamburg that traveling time will be 2 and half hours from the current 4 and half hours. So, airplanes connecting the 2 cities will suffer from passengers reduction, because many passengers will take trains or ride cars.
