A key part of ongoing construction work to complete the new metro station at København H - the metro station at the central railway station in Copenhagen - has opened with access to a wide tunnel under the platforms of the train station so that passengers can go directly from the metro trains to the platforms for suburban and national and international trains.

Until this tunnel opened, passengers from the metro had to go up to street level and then cross over a road and go up a flight of steps to get to the main station concourse before then going back down to the train platforms that, at the central station, are below street level.

Now, as you come up the escalators from the metro platforms, there is a large circulation area just below street level and, from that lower circulation level, you can walk straight ahead into the tunnel where there are steps and lifts up to each of the train platforms.

I’m not sure what to call this lower part of the metro station. The lower concourse?

When the first underground stations on the original metro line opened nearly twenty years ago it was the area where passengers bought tickets and where there were maps and information panels so it seemed reasonable then to call it a ticket hall.

Now, almost twenty years later, virtually everyone has an app on their phone and even the rejsepas - the plastic travel card - seems old fashioned so fewer and fewer people are buying printed tickets.

As long as you check information about which platform you want for which suburban train service, it’s a quick and easy way to avoid the people milling around on the busy station concourse and, the other way round, if you arrive in Copenhagen on a train then now there is a quick way down to the metro.

If people wonder about the general process of planning and designing then most would surely think about what happens out at street level - the part they can see - but this example shows just how much thought and work and money goes into threading together the new and the old parts of the infrastructure of a densely built and busy city.