Longest road and rail tunnel is being built under the Baltic Sea
30 comments
·March 10, 2025kryptiskt
L3viathan
> more people have an intuitive sense for how heavy a ton is compared to elephants
Yeah, I think most elephants don't have a good sense of _any_ man-made unit.
usrusr
There used to be train service on that ferry as well. Fond memories, in particular from the time when it was operated with the ICE-TD pseudo HSR (a diesel train, because German railroad is embarrassingly allergic to investment into any parts of the network that might be involved with crossing borders). Train goes into the ship, passengers disembark the train to stroll around the ship, just enough time passes for two cans of Tuborg out in the wind (benefits of not driving) and then it's back to the train again.
robin_reala
I take the Copenhagen <-> Hamburg train a few times a year, and this will make a pretty major difference on the Skåne / Germany journey. Though next time I’m taking Snälltåget over night, so maybe that’s easier still?
IsTom
What's the mass of an unladen elephant? An Indian elephant or an African elephant?
yread
This is a better article with a map
https://www.geoengineer.org/news/casting-of-fehmarnbelt-tunn...
vintagedave
> The Fehmarnbelt tunnel is going to be placed on a dredged tunnel trench, more than 90% of which has already been completed.
This is fascinating. I had thought underwater tunnels were always creating by boring, like the Chunnel was. But this looks like they're dredging a trench, placing cast concrete segments in it, and then filling in over the top. In order words, much like how the first subway tunnels were built a century ago on dry land, but now underwater.
I wonder how it's reliably kept waterproofed (on the span of decades or centuries)? How are the segments joined and sealed?
m4rtink
It is now done quite often for tunnels crossing rivers - just build the tunnel in a bay next to the river, then fllod it, float the tunnel in place and sink it to the trench, then cover with ballast and cover the trench. One of the Metro river crossings in Prague is done like that.
As for longevity - it is not that different from normal tunnels. Those also need to be often heavily waterproofed due to groundwater (under quite some pressure if you are tunneling under a lot of mountains!) and various underground springs you might tunnel into. So even "regular" tunnels that are blasted or bored often first have to fill the stabilized cavity with hydro-izolation and then actually build the actual hermeticaly sealed tunnel tube inside that out of concrete.
euroderf
So the segments are allowed to fill with water, and then at the end it is all pumped out ? Or is each segment wrapped in plastic when it is dropped into place, and then they are somehow linked together without the plastic causing problems ?
billpg
Thank you. I read that the tunnel "will link Denmark and Germany" and I had to check a map to confirm that yes, they are already linked. By land. By a lot of land. You're not experiencing memory loss.
keiferski
If this is the route I think it is (Copenhagen to Hamburg), I rode a train on that route about ~8 years ago. It was memorable for the fact that the train itself pulled onto a ferry boat. Pretty cool as a tourist, but I can obviously see how a tunnel would save a ton of time.
robin_reala
The ferry was cancelled a few years ago: the train route is now east all the way across Denmark to Kolding, then south all the way down to Hamburg.
null
Mashimo
2 year old 30 minutes documentary about it: https://www.youtube.com/watch?v=QiYvXKQksgI
Regular official small update videos: https://www.youtube.com/@FemernAS/videos
It's interesting how they build the concrete parts and then "just" sink them :D
lolc
I was wondering why they stopped publishing videos in 2024. They haven't, they switched to Vimeo: https://vimeo.com/1053667887 Here's the last video I could find, showing the first full-length elements floating in the basin before the factory: https://vimeo.com/1053667887
r3ctilinear
I hope it's not vulnerable to anchor drag 'accidents'.
hagbard_c
Of course it isn't, it is a tunnel not a cable. That said it could be vulnerable to 'Nord Stream 2' type actions given that it is built using prefab tunnel sections which are sunk down and connected. It would not take that much of a breach to flood the tunnel and make it unusable.
m4rtink
Afaik unlike Nord stream the tunnel sections will be burried in a trench, under a lot of both rock ballast (so they don't float back up) and soil. Not impossible to breach of course, but requiring either a lot of some very serious military grade explosives (earthquake bombs, just underwater, somehow) or a very auspicious drilling rig.
lexicality
Slightly more info with pictures on the official site: https://femern.com/the-construction/building-the-tunnel/
dinkblam
> […] is one of Europe’s largest infrastructure projects, with a construction budget of over 7 billion euros ($7.1 billion).
the berlin airport was more costly
AlecSwanky
"... one of..."
dvh
> World’s longest road and rail tunnel is being built under the Baltic Sea
> The tunnel, which will be 18 kilometers long
> By way of comparison, the 50-kilometer Channel Tunnel linking England and France, completed in 1993...
Am I missing something? 50 > 18
docdeek
Channel Tunnel is rail only; 'road and rail' probably used here to mean both means of transport.
librasteve
yeah - iirc the concern was that car drivers would be too unpredictable / bored driving 21 miles in a tunnel - so you just drive your car onto a train
wkat4242
Also, it could cause messy accidents that are hard to reach. I think it was a good choice, if you see what happened in other long road tunnels: https://www.theguardian.com/world/2001/oct/26/jonhenley1
The Chunnel had a train fire once but it was not as bad.
lukaslalinsky
I've been through the Austrian Arlberg Road Tunnel a couple of times, which is just 13km and I was super tired from the hyper focus, as I was leaving it. Can't really imagine doing it for 50km.
wkat4242
And said train is a tunnel too, you can just drive though it. Even has two levels in the car segment (not the truck one obviously). It's really cool.
jamwaffles
I suppose they're being pedantic in that the Channel Tunnel only carries rail traffic.
voidfunc
The Chunnel is rail only.
null
I live in southern Sweden and while stopping at Bordershop and waiting for the ferry is not the worst thing in the world if you're going by car, this will be a huge improvement for traveling to Germany by train.
"Weighing in at 73,000 metric tons each, they will be as heavy as more than 13,000 elephants."
I'm pretty sure more people have an intuitive sense for how heavy a ton is compared to elephants.