An Environment that cannot be changed invites its own destruction. We prefer a world that can be modified progressively against a background of valued remains, a world in which in which one can leave a personal mark alongside the marks of history.
--Kevin Lynch, “What Time Is This Place?”, cited in Roberta Brandes
Gratz’s “The Living City”.
Similar to what modern urban planners had repeatedly advocated that the practice of planning should continually evolve as a process, Alexander (1987) pointed out that urban design should be likewise. To such a notion, Jackson (1972) added that:
"the city of tomorrow is something which is slowly and continuously created. It may contain new ideas new thoughts, but it is not a new creation because of the process of continuity and through the regular addition and frequent amendments to an existing urban fabric... The future exists in the city of today, and as the circumstances of today move forward inexorably into the city of tomorrow, society can if so wishes bend, control, direct and lead the city as it now exists towards its horizon”.
Consistent with the above is what Shirvani (1985) emphasized that urban design extends in both time and space and therefore, the solutions put forward by urban design planners must not only respond to the needs of the present but should also be able to foresee the needs of the future, and, the solutions developed to respond to issues in one place can be used only as a basis but will need to be reconfigured to fit the unique requirements of another place. This, in essence points towards the concept of sustainability.
The key to sustainable urban design is responsiveness (with due reference to the concept of responsive environment propagated by Bentley, et.al., 1985), that is, to draw designs not too constrained as to just respond to a specific need of a specific individual or a homogeneous group at a specific time but rather should be flexible and generic as not to be exclusionary and time bounded.
The exclusion of other groups does not only happen because walls were built or gates were installed. Often, the built form can exclude people by not being able to resolve conflicts between car and pedestrian, by not being considerate to the needs of the disabled, and by imposing too much order and neatness. A pitfall to an urban design planner who had been car-dependent all his life is to design something which will tend to be pro-car. Moreover, without the prodding of more sensitive people (who normally would be our everyday citizen and not those who are in the saddles of power), a physically-able urban design planner can tend to disregard accessibility for those who are physically impaired. Being exclusionary often is not intentional. It becomes a tendency as may be dictated by how far one has gone and how many cases one has seen. It is like an economic consultant who has not gone to other countries and experienced the realities of life there but is prescribing solutions to their problems. That is why ,an urban design expert, to really be effective in his craft, should go out of his office and look around, feel, and if necessary, suffer from the common people's standpoint. This is what sociologists would term as the participatory approach to sociological research wherein they go out and be beggars in the streets in order to analyse the situation of street people in the social fabric. The importance of the information a professional planner can gather while being really there is incomparable and can not be learned in the classroom. This bit of knowledge, combined with what others have discovered on their own can make up a set of realistic objectives which the group can aim to fulfil as they draw the design and build things from the ground.
It is important to bear in mind that what makes a structure essential is its usefulness in the public realm. A structure with maximized accessibility and permeability can sustainably be useful because of the very fact that it does not create nuisance to everybody, and it does not just serve only a selected few. It does not hamper people's movement but rather, it can actually aid them. As regards usefulness over time, the concern is not just to secure the physical integrity of the structure (resistance to earthquake, typhoon-proof, and so on) but also to make the design flexible so that it can easily be altered to suit changing needs. A house may need to be enlarged as the family grows, a wall may need to be knocked down, or a room may need to be converted to a home-office. A sustainable design can foresee all these probable needs in the future and can provide for them in the current format. In buildings, the sustainability of usefulness may be provided for by considering access, building depth, height, hard (lifts, stairs, vertical service ducts) and soft areas, and active and passive areas. Organizing the inside of the building can give rise to robustness, it being the characteristic of being able to offer many different uses/purposes to its users (Bentley, et. al., 1985). Again, urban design planners can have a very limited view about what would be the future needs of the family occupying a certain house. The limitation can be caused by the extent of what one has experienced with his/her own family, for instance, he/she grew up in a nuclear family and would fail to envision the needs of an extended family).
To reiterate, because urban issues evolve, the expertise and knowledge of urban design planners should likewise do so. To be able to plan and design in a continuum, they have to accept that learning is also a process and ideas will have to be kept up-to-date with the changing urban setting.