I wonder what the relationship is between the word engineering in the sense used here and software engineering?

I am amazed how bad software engineering has become with constant updates of software because of “improvements” or because there has to be constant release cycle else the software is unmaintained or bad.

While this kind of engineering is designed to be untouched for the next 15 to 30 years. Minimal maintenance is needed and certainly the concrete doesn’t need updating every second week because concrete has suddenly “improved” or there was a bug in it.

It’s become the norm to release bad software and fix it later, I hope this norm does not make it to real engineering.

Do you have a source for how little maintenance this will need? I imagine there will be teams of people continually employed for regular maintenance and operations. Concrete does develop “bugs” in the form of cracks, chips, or other damage that needs to be repaired.

While software engineering certainly deals with different constraints, I don’t think this is a fair comparison. When stakes are low (as they are for most software engineering), different precautions are appropriate. The aerospace or financial software engineering worlds might be more comparable here, and the engineering for those systems looks quite different as a result.

See also: https://www.jerf.org/iri/post/2026/programming_is_engineerin...

Definitely I am making a broad assumption with many specifies where one can say "but what about X,Y,Z". Certainly, there are buildings that fall down and bridges collapse but what is the trend? Is software engineering getting better or worse?

From the linked article:

> And I would say that the success of AI coding agents has proved once and for all that we had successfully built an engineering discipline so strong that we are also the first discipline that has been able to successfully run AI at large scale within our discipline.

Yet we have no real clue how AI works or how to debug it, it's a brute force solution to everyday problems. Daily there are new examples of AI "escaping" its enforced cage. Why? Why doesn't AI "just work"? Because we don't truly understand AI.

I think AI is exactly the opposite to "true" engineering where one understands the system and can reproduce it. After all, retraining the AI will probably give you a completely different AI even if the training data was the same.

Software is super complex and cheap to update. Engineering like this, however difficult, is not that complex and it's very expensive and difficult to update.

We take advantage of the situation. If we invented some way of e.g. "growing" structures that turned out to be much cheaper we'd probably adapt our attitude to changing them.

Software isn't inherently complex, it becomes complex. Because it is iterative. Because we keep making demands of it that weren't planned.

Imagining building a bridge and then in the middle someone comes along and says it should also be a tunnel. I think therein lies a main difference to engineering and software engineering: planning and sticking to a plan.

Another thing are incentives: real engineering has real incentives to do it right, else you will get sued - by the families of those that died. Software engineering does not have this incentive to get it right.

When you say Engineering is not that complex, have you taken into account corrosive sea water, pressure, currents, what it means to make repairs and maintainance down there etc? It is difficult, because it deals with a very complex world full of physics, chemistry and even biology in a way that does not allow errors.

Engineering doesn't seem complex because there are centuries of learnings behind it. Those learnings become rules and suddenly it appears "simple" because no one debates whether to use wood or concrete when building an undersea tunnel!

That horrible website overrides web page scrolling and disables pinch zoom. Bad!

First it gives you a popup saying i'm not in the US and would I like to visit the global site?

In my experience that means they send me to the other site that doesn't even have the article i clicked to, or even if it has it they can't redirect me to it.

Very much depends on the site - certainly there's plenty that are annoying in the way you describe, but there's also plenty (I wouldn't be surprised if either side were the majority) that will take you to the exact same content on the more local version of the site.

Very nice video explainer https://public.skyfish.com/p/sundogbaelt/2675422/70675433?pr...

Here's a similar video for BART's Transbay Tube, which was built in a similar way.[1] The major differences come from building in an earthquake zone. The Transbay Tube is mostly steel, rather than concrete, for flexibility. There are expansion joints. And the Transbay Tube sits on a gravel and sand base rather than hard rock, on purpose.

The Transbay Tube sections were built in the Bethlehem Steel shipyards in San Francisco. A museum opens this month to commemorate that shipyard. It's in Dogpatch in SF, if you know the area. The shipyard still has a submersible drydock, but it hasn't worked in ten years and will be demolished soon, hopefully before it sinks.

The SF Bay Area once had far more heavy industry than most people realize.

[1] https://www.youtube.com/watch?v=247JT7ctQ_I

[2] https://bethlehemshipyardmuseum.org/

It's not in an earthquake zone, but isn't the Scandinavian continent still rising at a surprisingly fast rate? I wonder if that could affect the engineering of the Fehmarnbelt tunnel, in an "in x years one end of the tunnel will have risen n centimeters compared to the other end" way. It's probably such a small amount it's well within levels where regular maintance will cover it anyway, but I'm still curious.

Today I learned the Transbay Tube is the longest immersed tube in the world. Given that it opened in 1974, it presumably has held that record for 52 years!

Can anyone from the region comment on the status of plans for the landside linkup on the German side? Last time it made the press it was because the project was at risk of seeing the Danish tunnel finished before Germany could tell not even when but if a linkup would ever make it across bureaucratic hurdles. Almost like a Darien Gap made exclusively of red tape.

It's not really clear, the German part was going slower than the tunnel, but now that the tunnel is also delayed by at least 2 years, who knows maybe they are in sync again ;). The road link seems to be going much faster than the rail link on the German sinde, which won't be done before 2032.

You mean like the Brenner Base [Rail] Tunnel which will connect Austria and Italy?

Germany seems to be stuck at the "studying" stage before they improve the relevant rail links on the Grafing–Rosenheim–Kufstein route.

https://en.wikipedia.org/wiki/Brenner_Base_Tunnel

> The Fehmarnbelt Tunnel will complete the high-speed rail connection between Stockholm and Hamburg.

Not really, mostly cause Sweden don't want to build high speed rail, even when EU would have paid for a big share of it.

I'm amazed that engineers can make submerged tunnels work and that leaks don't (literally) sink the whole plan.

The Transbay Tube carrying BART across the bay is immersed tube. The sections were welded together by divers. The sections were filled with water and then pumped out.

Fehmarnbelt tunnel sections are concrete. I couldn't find how they are connected by concrete would make sense.

A video posted in another thread says the segments are sealed with bulkheads, floated into position, submerged by allowing water into a ballast section, dropped into place , aligned with pins, drawn to the next segment with hydraulic jacks, and sealed to it with rubber gaskets. Then the bulkheads can be removed. The gaskets also allow for some thermal expansion.

I'm curious what the lifetime of those gaskets might be and how you might maintain them.

They are GINA gaskets[0], they were supposed to last 120 years[1], but it has recently been shown that they may deteriorate faster than previously expected due to being under constant compression[2][3]

[0] https://www.trelleborg.com/en/marine-and-infrastructure/medi...

[1] https://www.trelleborg.com/marine-and-infrastructure/-/media...

[2] https://www.sciencedirect.com/science/article/abs/pii/S08867...

[3] https://dailygalaxy.com/2026/03/rubber-used-in-undersea-tunn...

The "ballast sections" may act as bilges, so that any leaks will accumulate there and can be pumped out. 100% water-tightness is not essential. Occasional re-grouting/caulking of the joints may be good enough.

I figure once you join them, you could also apply waterproofing to the outside as well, no?

Maybe. What would that look like, adding more gaskets on the outside? That sounds even harder to maintain since the only way to get access is diving.

Some kind of goop that would get very slowly squeezed into gaps by water pressure ?

Sealing is really not that difficult if you have access to the high pressure side. The hard part is identifying the location of the leak. In sum, this means that they have to absolutely nail it, on the first attempt, for the bottom part that is resting on the sea floor. If they can to that, the rest of the circumference will also be so good they don't have to even think about fixability.

Here’s a fun video about how one sunken tunnel was built in Vancouver back in the 50s. https://youtu.be/A1igKk8eK0M

There's no need to write "are you drunk?". Anyone can write a typo, or simply be mistaken. Treat people respectfully.

Agreed, I got carried away

"Immersed". The channel tunnel was bored below the sea floor.

52.6B krone for 18 km

8B USD for 11 miles

CACHSR IOS 36B USD for 171 miles.

The Merced to Bakersfield IOS looks like a bargain on a distance basis. I have no idea of the carbon offset or passenger time saving versus flying of course

The building of this tunnel will likely create way more CO2, than can be saved by providing a more direct route and avoiding ferries

(german source ... and very critical of the project)

https://www.nabu.de/umwelt-und-ressourcen/verkehr/verkehrsin...

Personally I like the concept of having a more direct access to scandinavia and see lots of other positive long term effects.

From a Danish perspective I don't really see any positive long, or short, term gains from the Fehmarn tunnel, but I also live in the wrong part of the country.

This is a tunnel for Sweden, Norway and Copenhagen, it's moving the center of everything in Denmark closer and closer to the center of Copenhagen, completely disconnecting the rest of the country. A few days ago a new train start running Copenhagen to Oslo, a seven hour trip. That's the same time it takes me to get to Copenhagen by train within Denmark. Everyone is happy that you can "Get on the train and just pop to Hamburg, Berlin or Prag", but you can't, only if you happen to live in a few select spots does that work. It's a multi-day journey with a layover within the country if I want to leave by rail.

Internationally this is a great project, internally in Denmark, it's going to make international train travel worse for the majority of the country.

I really hate how German environmental activists resort to hyperbole and alarmist language by default when voicing concerns. This only makes it harder for me to take them seriously.

And then there is this tried and true tradition of commissioning studies with the sole intent to support a predefined viewpoint rather than taking an unbiased approach. This makes it so hard to trust any information when political arguments become heated.

To make the connection back to the tunnel: it consumes a huge amount of concrete and that releases the associated amount of CO2. Thisnpart is fairly easy to estimate. But estimating the impact on traffic emissions is fraught with issues. There are so many assumptions about lifetime, amount of traffic, types of vehicles that I can easily imagine the error bars to stack up to the point where a little tuning of model parameters gives just about any desired result.

Agreed to that, but they are right with stating, that digging up so much ocean soil in a direct line might disrupt entire maritime ecosystems.

They are not really comparable are they. One is a rail connection over land and the other is a 130ft deep tunnel for rail and road traffic.

Well, if we’re comparing CA infra costs, for a more 1-1 comparison you can look at the $9.7B Los Angeles is spending on building out a long-awaited subway line (phase 1 of 3 opened Friday!) and see how tunneling underwater looks like a bargain in comparison.

https://www.latimes.com/california/story/2026-05-07/los-ange...

1USD = 6,35 DKK