Mark Hünermund Jensen

Dig deep: Copenhagen Metro

Today, we'll take the "dig deep" a little more literal, as we travel under Copenhagen's surface. We'll ask questions like: Why did Copenhagen build metro in a what was pretty much wasteland? How were tunnels dug out under a city which is a millenium old? And what makes Copenhagen Metro so special?

The political process

First, let's stay a few minutes above ground to discover how the metro even came to be.

In 1947 the so-called "Finger Plan" was introduced, as a strategy for the development of public transport in Copenhagen and the capital region. The key idea was that the commuter train network, known locally as the "S-trains", stretched out in five main lines (five "fingers").

Copenhagen primarily resides on the island of Sjælland (eng. Zealand), but also the northern part of Amager. If you look at the image to the right, Amager island begins where the palm of the hand is. At the time, Amager had a very poor infrastructure, and was for that reason not even meant to take part in the Finger Plan (as seen in the image).

But with gracious help from a bridge to Sweden (Øresundsbroen) and Copenhagen Airport; both Amager "residents" and both of very high importance to the infrastructure, Amager developed more wealth and infrastructure through the following decades.

In the early 1990ies Copenhagen turned its attention to the Ørestad district on Amager. At the time Ørestad wasn't much more than grass and hills, grasshoppers and hillbillies.

In 1993 the Ørestad Development Corporation was founded, and they had no plan to leave the bare land the way it was. Instead they would apply two concepts as the seeds to grow new city: Transport oriented development (TOD) and new town development. The idea is, to put it simple, to construct the transport system first, and let that act as the corridor and motivator to attract residents, companies, etc.

In the mid-90ies it was decided to kick-start this urban development, by building a metro. ØDC intended to finanse the metro by selling off lands, whose value was expected to increase with the growing importance of Amager, and of course from future ticket revenues. A "small loan" was taken, and expected to be paid back over 30 years.

Brief Construction Timeline

Construction began in 1996, and in October 2002 the first line from Nørreport to Vestamager (green line on the map) and Lergravsparken opened. Through 2002, 2003 and 2004 more stations and line segments opened as they became ready.

In 2007 the line to Copenhagen Airport was completed (yellow line).

Of the first 22 stations, 9 are underground. The remainder of the network is light rail tracks.

In December 2005, plans for the City Circle Line (blue and red lines) were finally agreed on, but construction will not complete until 2019. The price tag on this baby is estimated to around 13 billion DKK. The red segment of The City Circle is entirely underground. The blue line will be expanded into the sustainable building area Nordhavn (North Harbour), and later into Sydhavn (South Harbour).

The City Cirle is largest construction project in Copenhagen in 400 years, where Christianshavn was developed. When the two stages currently in development opens in 2019, the map of the Copenhagen Metro is as seen on the image above. As of 2016, the green and the yellow lines are active.

Station shafts

The first thing that happens, when new stations are built, is that archaeologists are invited to the site. This has led to a few interesting finds, including old city gates9, dating back 1,000 years. And not surprisingly, everyday items from the late Viking age have also found.

But another task looms before stations can get dugged out. Relocating kilometer's worth of pipes and cables, from the milimeter thin to the meter thick, anything from internet cables to water pipes. The total cost of the cable/pipe relocation is around 1 billion DKK for the City Circle.

The next stage is the actual excavation of the station shaft. CMT (Copenhagen Metro Tean) utilizies a method called Cut & Cover.

Per the method, the team initially drills out what becomes the walls of the station. This is an essential first step to assure that ground water doesn't leak into the construction. The walls are then reinforced with concrete and steel.

When a square of meter thick wall is dugged out and filled up, a "lid" (the roof of the station) is created to hold the walls in place, and an additional bonus is that it reduces the noise of the construction, as the machines start digging out the actual shaft.

As the digging progresses, beams are installed to further strengthen the construction, and hold the installed walls in place.

Once the station box is dug out the construction is put to a temporary halt, until the tunnelling teams pass by.

Protecting landmarks

When you dig, even with cut & cover, you have to take extremely good care to the surroundings. For instance, while building the station near Marmorkirken (The Marble Church), it was decided to abandon the traditional station design, and instead build a station with two floors4. Additionally, this makes it the deepest of all stations, with a depth of nearly 40 meters.

Marmorkirken became centerstage for controversy in 2009, following a collapse in Köln, Germany. Metroselskabet, who manages the construction and operation of the metro in Copenhagen, were alledegly aware of the immediate risk to cause cracks in the church, but insistingly still chose the location for a station between Østerbro and Kongens Nytorv.

But to make matters worse, some claim the location of the station doesn't even comply with the design principles laid out by Metroselskabet. The rule of thumb is that there should never be more than 600 meters between stations. But Marmorkirken is 900 meters from Østerport station. So people asked: Why is Marmorkirken even a point of interest? Why is Metroselskabet running the risk?

It should be noted tha houses and buildings were damaged during construction of the first metro lines in Christianshavn.


Copenhagen didn't intend to build the first tunnelless metro, so they brought in the heavy machinery: Enourmous machines called Tunnel Boring Machines, or TBM for short. Beasts that're around 140 meters long and weigh over 600 tons.

On the front TBMs are equipped with a cutterhead, and the remainder is basically a small factory in itself, with mechanics that can transport the dirt away, construct tunnel and supply itself with water, electricity and other goods required in the deep.

TBMs are by far a new invention. The first one was introduced in 1825. But they have, like most other technologies, evolved quite advanced.

The Copenhagen underground consists primarily of calcite, which is a quite stable material. The calcite layer originates from the Danien time period (coincidentally named after the Latin name for Denmark) which is from around the time the dinosaurs went extinct.

A TBM's cutterhead crushes the material ahead of it. The crushed material is transported away on a conveyor belt (also part of the TBM), and delivers it to smaller transport vehicles, driving it out of the tunnel.

The dirt is transported to Nordhavn, where it's used to expand the artificial island. The City Ring project alone will provide around 3,100,000 tons of dirt, after having dug out aroun 15 kilometers of twin tunnel and 17 station boxes.

Reinforced conrete segments are built above ground and then transported underground to the TBM. These segments are fed to the TBM, who will position the segments to form a ring - and ta-da: A little more tunnel is built. Each ring consists of six segments with an out diameter of around 6 meters. So, you might be pumping lots of iron in the gym, but a TBM lifts massive concrete blocks, and puts them together with milimeter precision. Also, it eats children for protein.

The TBM then moves on and repeats this process. It travels 15 to 20 meters per day and is operated 24/7 by a team of 10 to 15 people.

In Copenhagen's metro, the tunnels vary from 25 to 33 meters depth. Stations are always located on a "hill". This is to let the train drive downwards during acceleration, which saves energy. Ah, the ever so politically correct, environmental friendly Denmark, am I right?

Bonus fact: The trains are washed in collected rain water, which only adds to the aforementioned greenness of the metro.

Every TBM is controlled by a pilot. TBMs manage milimeter precision underground navigation, not by GPS, but by using the already excavated and reinforced tunnel as reference. Combined with laser reference points, gyroscopes and more, it knows exactly where it's headed. Station boxes are already dug out when a TBM reaches it, so for that very reason it's of high importance that angle and level are completely on point, as the TBM breaches into a station box, and hence completes the segment of tunnel.

When the TBM has left the tunnel and it has been properly reinforced, the rails are added the tracks.

Wrapping up

One of the most celebratory moments are when TBMs breach into station boxes.

This is the point where a new leg of tunnelling starts, and the point where the construction teams can complete the station, by adding actual wall, station floor and interior. This includes installing the escalators, elevators, ticket machines, etc.

Watch as the TBMs breach into the station shaft at Copenhagen Central Station (Audio in Danish):

The stations of the original two lines are with full intention very similar in layout and style, to ease navigation for passengers between stations.

The layouts were chosen based on advanced computer simulations, of how passengers move through stations.

It's a wrap!

The journey from 1992 to 2016 has brought many ups and downs for the metro, which with its young age still impresses on an international stage - and the journey has only just begun, with plans that span all the way into the 2030ies.

Now, when all is said and done, let's take a look at the final product. Here's the basic design for the underground stations:

And even though we havn't really covered them in greater detail, here's some photos of the beautiful overground stations:

In the first two metro lines 9 stations are underground, and the remaining are overground. All underground stations are in the city center. The City Ring will itself consist entirely of underground stations, however, as the branches that derive from the City Ring will head back above the surface.

Driverless trains

One of the most notable and impressive features of the Copenhagen Metro is the automated, driverless trains. The Copenhagen Metro is a so-called GoA 4 (Grade of Automation 4) system, which is the highest grade in existance. Basically, it means that both operation of doors, signaling and driving the train itself is fully automated.

The automated trains will not be covered in further depth, but if you're unable to actually try the Copenhagen metro, you can enjoy it from the seats in a YouTube video (the last 1 minute is particularly nice, where you get to see how Ørestad has developed):

Accidents, incidents and drama

In spring 2014 concrete elements exploded out of the metro construction site in the heart of Copenhagen, Rådhuspladsen (the city square). The concrete elements struck several cars parked in the street Vestergade. No people were harmed.6

Pictured is what the the Rådhuspladsen metro station will look like, when it's not busy blowing stuff up.

On a more sad and dark node, the underground metro stations have been the stage of suicides, a couple of times. Most were carried out by jumping from the top floor, which has a huge open hole leading down to the bottom floor. This jump is around 10 meters.7

I personally remember riding the metro, many years ago, where we were about to stop at Kongens Nytorv station, but the train drove past it. It turned out that a woman had just killed herself - also by jumping from the top floor.

Also the overground stations have seen suicides and suicide attempts. In 2011 a person jumped in front of a train, and was killed. This is particularly brutal, since the trains are driverless, and passengers look directly at what's ahead of them; Meaning that the people in front have seen the person strike the train and die, right in front of them8.

Trainsurfing is when you jump onto a train and hold on while it's driving. The Copenhagen Metro company is aware of a few situations, but I haven't been able to find news regarding any deaths. Since there's both underground and overground stations, it's actually possible for daredevils to jump onto a train from a relatively unprotected overground station, and drive with it into the tunnels. Allegedly there's only around 20 to 25 centimeters space between the train and the tunnel walls10.

When you race the tube, you try to run from one metro station to another faster than the train gets there. It has probably deen done several times, but a guy chose to document it with a GoPro from Fasanvej St. to Frederiksberg St. Watch it happen.

Future Lines

In 2013 it was decided to expand the City Circle to accomodate the Nordhavn (Northern Habour) district.

In 2015 the expansion to Sydhavn (South Harbour) was finalized, with a budget of 8.6 billion DKK and completion in 20232.

Plans to expand towards Brønshøj and Gladsaxe were scrapped. However, other projects reaching into suburbs of Greater Copenhagen are still alive, including a line to Brøndbyøster.

There has also been talks about expanding to Malmö in Sweden. "But don't you already have a bridge?". Yes, we do. But it may not sustain the demand for more capacity. But these plans are far into the future, and currently it's most likely not reality before the 2030ies1. But let's wait and see if we'll really need a metro, and just travel to Malmö by jetpack or teleportation.

The stations on the first two lines are extremely similar in layout and design. This move was made to make it easier for passengers to navigate the stations, but it also made the metro very sterile.

This is something Metroselskabet chose to change with the City Ring, which introduces more colorful stations, and every station has a unique theme and coloring.

Final Remarks

I've been fascinated with the Copenhagen Metro ever since I rode it the first time. Back then, I got very interested in how it was built, the political process and all that. Then there has been a sort of "radio silence" on that interest for a long while. Many years. It sparked again recently, and that's when I decided to write this post. Now, it's probably out of my system ;-)

I really hoped you enjoyed this read, and I hope you learned something interesting!