The 21st Century will be either the century of sustainability or the century of collapse. It will be either the century where the continuation of the unsustainable economic practices of today precipitate irreversible catastrophes, or the century where small local successes in implementing sustainable practices and processes proliferate to transform the entire global economy to a new, balance-seeking relationship with our natural ecosystem. It will be the century where either the analytical, reductionistic methods of science and industry which are the sources of both our progress and our increasingly unsustainable way of life will continue as the central economic paradigm, or the century where a new integrative economic paradigm emerges which promises to put humankind and its processes in a balance-seeking relationship with the natural environment, whose health is the precondition for all human activity.

We are faced with the choice of either continuing our descent into the realm of unsustainability while continuing to deny that it is the consumerist/materialist path itself that is the problem, or we can shift to the new emerging paradigm, a paradigm based on the same principles and processes as those that underlie architecture and design. At present we are not aware that there is a real choice to our current path. It is therefore the primary challenge facing our generation to develop the alternative to decline, not just on a theoretical basis, but as a real place: The Sustainable City. It is an idea whose time has come. It will take very little to precipitate that paradigm shift. It took only one steam engine, one light bulb, one Xerox machine. It will take only one city operating within the limits of its resources and its environment: one Sustainable City, to prove to all the others not only that sustainability is possible, but that it is the only possible way in which the cities and their economies may be designed and managed. Fortunately, an operational theory of the sustainable city is in place and has been embedded in the European Charter of Cities and Towns Towards Sustainability. Equally important is the fact that many towns and cities are moving to implement the Charter in actual programs and urban projects. This paper describes Vienna's Westbahnhof project, which may become the first project in Europe to fully implement the principles of the Charter and in so doing, become Europe's first modern sustainable city.

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The sustainable city is not a new phenomenon. Historic towns and cities around the world did not have a choice. If they existed for any length of time it was only because they were able to develop and maintain a constantly rebalancing relationship among their internal social and economic activities and externally with their natural and agricultural landscape. It is a tribute to our genius that we have been able to create an artificial economic system that has been able to operate on a new unsustainable basis for a number of generations. We have been able to do this because of the brilliant ways we have contrived to export the problems it has created to poorer, less defensible regions or to the future. But that future is rapidly approaching.

Our civilization is to be either lost or redeemed in China, the awakening giant. Should China continue along it present route, adopting the western model of production and western patterns of consumption, it will quickly destroy both its own capacity for sustaining itself as well as accelerate the deterioration of the unsustainable global material/economic system. It is ironic that in recent years China has been feverishly adopting the unsustainable western model at the same time that progressive institutions and cities in the west have been searching to find and implement the sorts of sustainable processes of life and production which until recent times have been the common local pattern within China. These sustainable local patterns of past cultures are very similar to the ways in which a natural ecosystem operates. Like an historic town a natural ecosystem is a strong local economy working as an interlinked network, typified by regenerative cycles of energy and material flow. In nature processes return on themselves: there is no garbage. Over time the diversity, the resiliency and thus the stability of the ecosystem increases.

The good news is that there is a strong global sustainability movement. The Earth Summit in Rio in 1992 and the Climate change conference in Kyoto in 1997 are just two of the many international activities that are building to confront our growing environmental problems. The bad news is that the principle vehicles being employed in this movement are the analytical, reductionistic methods that we would argue, have created the problems in the first place. This overwhelmingly quantitative approach insists that we must commit ourselves to do more with less, and less and less. While this approach offers successful initial steps (recycling aluminum, changing to fluorescent fixtures) subsequent steps become successively more difficult, more expensive and less effective, until a point of diminishing returns is reached long before sustainable balances have been effected. Equally troubling is that this pervasive quantitative approach is also a top down approach starting at the global level (Rio) and working its way down to regional and national programs of restriction and regulation. Such an approach is fraught with the inevitability of controversy and conflict (who is to make which sacrifices and on what basis) that are likely to defuse any initial momentum. In any case as the "Rio plus Five" conference has indicated, the record so far has not been promising.

There is an alternative approach which is less visible in the U.S., but which has achieved greater momentum in Europe. A major embodiment of this approach is seen in the already mentioned European Charter of Cities and Towns Towards Sustainability (The Aalborg Charter) which in contrast to the reductionist approach is place-centered (i.e. the city) and process oriented. This puts the Charter squarely in the realm of architecture and urban design and promises to extend both the nature and influence of those realms. The authors of the present paper were principal architects of the Charter, which has been ratified by more than 200 of Europe's most progressive cities.

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At least since the late 1980s, the sustainability movement has been organized around a minimalist, consensus definition advanced in the Bruntland Commission's report, Our Common Future, whose vagueness has be largely used to support the analytical, reductionistic approach to sustainability: namely, sustainable development "meets the needs of the present without compromising the ability of future generations to meet their own needs." We propose instead, an alternative course--a complete theory and process for generating and operating a sustainable city/region. It is based on Oikodrom's “Compass of Sustainability” and the Aalborg which in turn derive from the “Five Operating Principles for the Sustainable City”.

Here is that complete definition:

Sustainability is a local, informed, participatory, balance-seeking process, operating within an equitable ecological region, exporting no problems beyond its territory or into the future.

This definition has many implications which have been explicated at length elsewhere (see bibliography). Here is a discussion of some of the key points. The major challenge of our generation is to forge an equitable way of living on this planet, in our cities (for that is where we live), within the limits of nature. This challenge is seen as a design problem, a large part of which is an urban design, urban management and an architectural design problem. More importantly, the methods to be used in this process derive from and are much more akin to traditional architectural design methods than they are to science and its traditional methods. Sustainability is seen as a process for transforming society from an exploitative, consumerist enterprise to an equitable society where the balances between man’s enterprises and between man and nature are negotiated locally. Although such a process derives from traditional architectural design processes, a new expanded architectural design process is envisaged. Instead of relying upon the hoped for genius of individual architects, the sustainable design process will rely on the collective genius of all the individual stakeholders in the equitable ecological region (EER). Sustainability is a local process. This means a process conducted amongst all the stakeholders within a city/region. The simple determination of the land and resource budget available within this city region is found by dividing the total land area of the country (or the larger region, or the earth) by the population of the country (or the larger region or the earth) to determine the equitable land area per person. This figure is then multiplied by the population of the city/region to determine the land area of the Equitable Ecological Region (EER).

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This paper presents a prototype of the Sustainable City Implantation of the future, which the city of Vienna, Austria is interested in considering as a solution to a long standing urban problem, - the overbuilding of a major train yard at the Westbahnhof. Developed conceptually through numerous architectural design studio projects and field studies the Sustainable City Implantation (SCI) is inspired by the historic medieval European hilltown. This City-as-a-Hill prototype, rendered through a sophisticated and flexible computer systems dynamics model called the Sustainability Engine? presents a new holistic, people centered, urban vision. In the SCI sustainability is non-negotiable. This means that all major material flow processes are regenerative and the implantation is completely powered by solar renewable resources.

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A sustainable economy must be powered either by the sun or by the many solar derived processes. The solar energy movement has given architects and urban designers a great array of tools and alternatives in making our buildings and our cities more energy efficient. But efficiency as an end in itself goes nowhere. Instead solar, renewable and regenerative means are seen as the tools and catalysts for the larger agenda of the sustainable city. Under this expanded agenda, it is not automatically assumed that the more solar heating the better. Neither is the focus on the usual sub optimization routines of calculating what solar fraction or degree of insulation is most cost-effective within the given local conditions. The starting assumptions within the process of negotiating the sustainable city are completely different from those used in the design of an energy efficient building. Because sustainability becomes the overarching principle, other derivative conditions become non-negotiable. For example in a sustainable city, the minimum fraction of energy to be supplied to the city through solar-regenerative means is obviously 100%. While this may seem overly ambitious from a conventional, energy limited, cost-benefit point of view, it greatly simplifies the concept while it mobilizes a new and expanded design process. It seems there is a great difference between marginal improvements to the unsustainable business as usual and doing things the way they ultimately must be done.

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Our proposal for a new type of city district combines some of the most compelling aspects of the medieval European hilltown with the best of modern processes and technology. Instead of the medieval city on a hill, this proposal is for a City-as-a-Hill whose outer surface in scale and texture resembles the pedestrian scaled medieval towns built to a human measure. Using advanced computer modeling software, which allows for the possibility of generating many varieties or models of such SCI's in an interactive and participatory manner, this new urban configuration creates many opportunities not possible in the modern unsustainable city. In our City-as-a-Hill model the outer (upper) surface of the city contains all of the dwellings and neighborhoods, the smaller scaled commercial and institutional activities and the network of public buildings and public spaces--that is, the streets, walkways, stairs and squares which give historic medieval towns their life affirming, pedestrian character. Inside the City-as-a-Hill, daylit by courtyards and light wells, is a series of concourses and gallerias along which are located the large scale commercial, institutional, and industrial spaces as well as the infrastructure and other activities necessary to support a modern sustainable economy.

Over the years in which these models have been developed, the structure and complexity of our studies have increased at many scales. A new concrete structural system with unusual flexibility which generates a complex family of building geometries is being used as the framework for both spanning the train tracks below and for creating the inner hill and the urban fabric above. This permits the negotiation of both level and sloping streets on the constructed hill, giving it the sort of three dimensional, organic character rarely seen in modern architecture and modern cities. More recently, the use of computers to assist in converting theory into practice has made it possible to increase both the flexibility and the complexity of the urban models.

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Behind the Westbahnhof, one of Vienna's main rail terminals, lies a train yard 1.5km long by 200m wide. For many years this yard has been a wound within the city, dividing a neighborhood and creating near slum conditions on either side of the yard. There have been many proposals to overbuild the yard but none has been either a suitable economic proposition or a sufficient urban contribution to be acceptable the city. The present proposal builds a glazed, vaulted train shed behind the terminal building at the east end of the site. It is in part in the tradition of the early glass train sheds still to be found in many major European cities, except that at the Westbahnhof the hectares of glazing contain integrated photovoltaic collectors which deliver a substantial percentage of the Implantation's energy requirements, while modulating the climate and quality of light entering the terminal. A pedestrian street starts from the terminal and runs the length of the site to the west, parallel to the tracks, rising up the constructed City-as-a-Hill at a gentle six percent slope. As it rises it crosses other horizontal floor levels and at every third level (levels 4,7,and 10) it passes through a public square or piazza. A streetcar runs along this otherwise pedestrian street and after passing through the main piazza (Hauptplatz) at level 10 it descends through piazzas at levels 7, 4, and 1 to join an existing trolley track at ground level. On the surface of the constructed hill is a human-scaled town with networks of streets, and stairs- piazzas and paths, weaving between three to five story neighborhoods of dwellings and a full variety of shops and services. Also on the hill's surface is a winter garden growing food year round, and a network of south-facing greenhouses. At the west end of the village is an east-west exchange center which is roofed by a large terraced ecological park, connected to the existing technological museum. At this end of the site from an existing park begins another sloping street which is more like a linear park culminating at a fountain at the level 10 Hauptplatz which is also an energy gnomon; that is, the height of the fountain is an indicator of the rate at which the Implantation is exporting renewable energy to the larger city of Vienna. Overflow from the fountain trickles down through the linear park, feeding various ponds and other green areas along its course. The roofs of the outer city are either glazed greenhouses or flat roofs which are all utilized either as private or semi private terraces, gardens, courtyards or public parks, playgrounds or piazzas.

Running almost the length of the site a three-story high galleria runs within the hill at level 4 and another shorter one runs at level 7 connecting the piazzas at those levels. Along these gallerias, daylit through courtyards and light wells from above, are all the large major institutional, commercial, and industrial activities as well as infrastructure, service, parking, tracks and transportation; activities whose large scale often disrupts the integrity of a traditional urban fabric, but which are necessary to sustain a modern urban economy. In the City-as-a-Hill they fit in very well, providing maximum accessibility without compromising its small scale, village character.

The Sustainable City Implantation is a totally urban construction, which multiplies value, in part because it multiplies real estate. Railroad services occupy almost the entire site at the original ground level, but there are additional levels of developable real estate in the framework above with their own appropriate functions and activities. Because it is completely urban, and has no open ground of its own, the Implantation is to be linked with a rural partnerland, which is dedicated to its sustainability rebalancing process. On this land most of the agriculture and energy from solar/regenerative sources would be negotiated with its urban counterpart. The urban implantation together with its rural partnerland would constitute a contained ecological footprint (appropriated environmental space), that is the combined land area would provide all the major energy and resources needs of this territorial partnership while resolving any ecological imbalances on site.

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Our proposal for a new type of city district combines some of the most compelling aspects of the medieval European hilltown with the best of modern processes and technology. Instead of the medieval city on a hill, this proposal is for a City-as-a-Hill whose outer surface in scale and texture resembles the pedestrian scaled medieval towns built to a human measure. Using advanced computer modeling software, which allows for the possibility of generating many varieties or models of such SCI's in an interactive and participatory manner, this new urban configuration creates many opportunities not possible in the modern unsustainable city. In our City-as-a-Hill model the outer (upper) surface of the city contains all of the dwellings and neighborhoods, the smaller scaled commercial and institutional activities and the network of public buildings and public spaces--that is, the streets, walkways, stairs and squares which give historic medieval towns their life affirming, pedestrian character. Inside the City-as-a-Hill, daylit by courtyards and light wells, is a series of concourses and gallerias along which are located the large scale commercial, institutional, and industrial spaces as well as the infrastructure and other activities necessary to support a modern sustainable economy.

Over the years in which these models have been developed, the structure and complexity of our studies have increased at many scales. A new concrete structural system with unusual flexibility which generates a complex family of building geometries is being used as the framework for both spanning the train tracks below and for creating the inner hill and the urban fabric above. This permits the negotiation of both level and sloping streets on the constructed hill, giving it the sort of three dimensional, organic character rarely seen in modern architecture and modern cities. More recently, the use of computers to assist in converting theory into practice has made it possible to increase both the flexibility and the complexity of the urban models.

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In subsequent stages of the work, the city models and their parts will become the framework for the integration of other systems including: mechanical, electrical, material and infrastructural systems, facilities management, information, energy and material flow models, economic activity, imports and exports (input/output) to the city, and the modeling of the ecological balances within the city and between the city and its rural partnerland. This will be done on a systems dynamics program we call the Sustainability Engine©. Our operational definition describes the Sustainable City Implantation as one which exports no problems to its larger environment or to the future and absorbs some of the larger city's problems while exporting to the city a positive sustainability quotient. Thus we set sustainability as the one non-negotiable characteristic and begin our other negotiations from there.

The Sustainability Engine© is the autonomic nervous system of the Sustainable City Implantation. Both during the design process and in the governance and management of the city the Sustainability Engine© houses the energy, material flow and process models that are studied and experimented with in the development of the city. As the city, its processes and industries are studied, the Sustainability Engine© provides frequent feedback on the ongoing state of the system and indicate the sectors where it is out of balance. It is also intended to provide many utilities to facilitate the balance-seeking, and negotiation, of the design process.

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The issue of urban sustainability promises to create the next major transformation both in architecture and in our cities. In many ways the Sustainable City will represent the rebirth of Modern Architecture. The Athens Charter became a disaster for our cities. Because of the mechanistic ways in which it separated functions and activities it reinforced the economic tendencies toward unsustainability. In contrast, the sustainable city will demand a dense, diverse, highly integrated urban fabric. It will demand a whole new range of architectural and urban form and structure. It will put architects and architecture at the center of a participatory process demanding the skills and creativity of all it participants. It will complete the agenda of Modern Architecture by making it whole.

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The European Charter of Cities and Towns Towards Sustainability (1994)

Stadthügel Westbahnhof: Ein Kostprobe, H. Dumreicher, R.S. Levine, Vienna (1995)

Does Sustainable Development lead to Sustainability? E.J. Yanarella, R.S. Levine, FUTURES (October 1992)

Don't Pick the Low-Lying Fruit: Sustainability from Pathway to Process, R.S. Levine, E. J. Yanarella, ASES (1994)

Cities and Regions: Co-Evolution Towards Sustainable Development, R.S. Levine, E.J. Yanarella, H. Dumreicher, Graz, Austria, 1998

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