____________________________________________

Examples

Presented next are three couples of examples of multiple (underground) land-use, one for each of the application area previously discussed. Each couple consists of a case situated in the Randstad and a case situated in Berlin. Berlin serves here as an point of reference. Urban planning policies in Berlin are mainly based on the multiple land-use. For instance, 90% of the 400 000 new homes needed in the German metropolis till the year 2015 will be built within the city's existing envelope, while only 40 000 homes are to be constructed by means of urban extension. There seem to be no best or worst case scenarios in both cities but, placed next to each other, the cases offer a good scoop of what can be achieved and what might be missed.

Tunnelling through a large and a small green heart
In the Netherlands, recent interest around the use of underground space sprang up in connection to the proposed construction of several large scale infrastructure projects, among them the `HSL': the high speed train link between the Randstad (Amsterdam, Schiphol Airport and Rotterdam) and Paris.
The project is considered essential for the economic strength of the Dutch metropolitan area, but at the same time spill over most of its negative consequences (like noise and spatial fragmentation) to the open countryside within and outside the Randstad. Public opinion forced a serious look to be taken at large scale underground alternatives.
In response, the Dutch government put aside 900 million Dutch guilders, or 60 billion Japanese yen, for the construction of a 9 kilometre long tunnel that will preserve the spatial integrity of the Green Heart. This decision serves as a major precedent, already having its effect on the planning of other parts of the track and also on similar heavy infrastructure projects. It is expected to do so for many years to come.
The tunnel will be constructed by the use of tunnel building machines, a technique relatively new to the soft soils in Holland. By gaining the much needed experience in a mainly agricultural area, the risks normally involved in densely built-up areas are dramatically reduced. But, exactly because of these rural building site characteristics, critics argue that the investment in underground space is misdirected here. They argue that the money would be better spent on the construction of underground mass transit in the one of the core urban areas of the Randstad.

In this respect it is interesting to take a look at the `Tiergarten', the main park in the heart of the German capital, many times smaller than the Green Heart of the Randstad, but just as important for the identity of the city as a whole. Since the downtown of Berlin regained its centrality after the re-unification of the two Germany's, the edges of the park have become the focus of frantic building activities, preparing for the relocation of the German government from Bonn to Berlin and compensating for the substandard quality of existing buildings in East Berlin.
In this same line of events it was felt that the main node for train services should be brought to this centre by constructing a new central station, north of the Tiergarten, the Lerther Bahnhof. To do so, it became necessary to restructure the urban rail system. In elevated position, the new railway tracks would erect a wall of infrastructure in the downtown of Berlin, right at the location of the infamous Berlin Wall, slicing off a vital part of the Tiergarten and splitting the city centre in two halves again. To prevent this from happening both the federal and the city government decided from the beginning to combine the railroads with two other infrastructure projects in the area (an urban motorway and a additional subway line), and construct them underground.

Here, interestingly, critics complain about too much emphasis on the city centre, favouring a more decentralised urban structure. In their argument there is also some resentment towards the relocation of the German government ,which it is feared will cause increasing congestion and a higher cost of living in the city. In this respect the project is mockingly called the Kanzlerbahn, the railroad of the prime minister, whose office will indeed lie directly above the tunnel system. Although there is truth in the reasoning, the critics do not mention that the government aims at a 80% share for public transport in the traffic movements in the centre and a high quality of public urban space. Both goals are rarely reached at more peripheral locations.

Underground stations: focus of urban development ór architectural design?
If we take a closer look at the underground traffic projects in the centre of Berlin, it will become clear that the underground infrastructure not only spares the city forest. The tunnel also serves the reconstruction of the central business district around the Potsdammerplatz which will accommodate about 20 000 workers and many more visitors, customers and business partners. To make sure most of them travel by mass transit, a four-track regional train station and a two-track subway station are under construction. These will be added to the double rapid-transit station and single subway station already in place. This makes up a impressive amount of underground space for mass transport. The multiple land-use in the close vicinity of the station, ranging from four basements down towards 21 storeys up, is even more remarkable. In comparison the architectural features of the underground station clearly lag behind. It seems like as though no attention at all has been paid to the relationship between the station underground and the city surface, to daylight entry and the identity of the station in its surroundings.

If we place the already constructed railway station Blaak in the heart of Rotterdam next to Potsdammerplatz, it may become clear what chances could be missed. Station Blaak is positioned along the four-track `Willemspoortunnel' that replaced a technically outdated and capacity-insufficient elevated railway that carved up the centre of Rotterdam for more over than a century and bridged the river Rhine2. The train station is connected underground to a subway line and aboveground to tram services.
To overcome the usual negative associations with underground stations resulting from the experience of poor underground spatial design, this time neither money nor effort has been spared. A massive void has been created that gives both entrance to the station and brings direct sunlight to the platforms 16 metres down below. A circular glass roof uplifted by a giant arc gives dramatic expression to the presence of the station in its surrounding. Although the station itself stands out as a fine example of well-designed multiple underground land-use, the focus of urban development shifted away from the station area before the completion of the tunnel. Municipal politics forced the development of the other riverbank3 to be taken up first.

Underground shopping: losing or gaining liveability in the centre
Comprising 200 000 m2 gross floor area, the Berlin `Friedrichstadt Passagen' stands out as a massive example of innovative use of partly underground building. It is built out of three dense city blocks (each 8 stories), placed upon 4 commonly shared basements. The 1st basement contains storerooms and building services. The 2nd basement houses shops, arcades and other public areas. The 3rd and 4th basement serves as car park.
While the basements don't contain inner courts and spread under the streets, the ratio between aboveground and underground floor area is 1:1, despite the 2:1 ratio between the aboveground stocks and basements. Unfortunately, because the public areas are placed on the second sub-level. No visual relation is possible with the city's surface. The internal urban space is automatically turned into closed privatised space at the expense of the liveliness in the streets above.

In this respect, the recent reconstruction of the Beursplein in Rotterdam might offer a more favourable concept. The shops and public areas are positioned on the first sub-level directly connecting to the city's main subway station. The public space is just only partly covered by glass, keeping full contact with daylight and the urban space aboveground . The liveliness underground adds clearly up to the public realm of the whole centre.