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1、 THE URBAN STREET BLOCK 9 INTRODUCTION The degree to which a city is sustainable is affected both by the form of the urban street block and also by the composition of the activities it accommodates. The way in which the street blocks are designed and the land use mix within street blocks also affect
2、s the quality of the built environment. Current conventional wisdom adopted by those in the field of sustainable development rejects the cruder notions of land use zoning, in favour of subtler urban structuring, based upon a mix of uses and activities. The traditional city with residential and offic
3、e accommodation arranged over ground floor shopping streets is often cited as a model arrangement for a lifestyle which is not dependent upon high levels of mobility. It is also argued that a city with a fine grain of land use, rather than the homogeneous zones of residential commercial or industria
4、l uses, common in modern metropolitan areas, is more likely to reduce the need for travel, and, incidentally, also be more likely to create an interesting and liveable environment. There is little doubt that a city is judged by the quality of its public streets and squares: by their form, the fac ad
5、es which enclose them, the floor plane on which visitors tread, and the great sculptures and fountains which delight the eye. It is, however, the size, function and structure of the street block which gives form to public space and contributes to the vitality of those spaces. This chapter examines t
6、he various ideas about the form and function of the street block and its role in structuring the city, analysing, in particular, the street block in a sustainable city. The street and the street block of the traditional nineteenth-century city received great criticism during the 1920s and 1930s from
7、 the leaders of the modern movement in architecture. Le Corbusier, for example, said of the street: Our streets no longer work. Streets are an obsolete notion. There ought not to be such a thing as streets; we have to create something to replace them (Le Corbusier, 1967). Gropius was expressing simi
8、lar sentiments: Instead of the ground-floor windows looking on to blank walls, or into cramped and sunless courtyards, they command a clear view of the sky over the broad expanse of grass and 193 trees which separate the blocks and serve as playgrounds for the children (Gropius, 1935). Projects of t
9、he time, speak most clearly to this aim of destroying the traditional urban fabric of the city and replacing it with ranks of unadorned blocks standing serenely in a field of green (Figures 9.1 and 9.2). Giedion, the apologist for the Modern movement in architecture is quite clear in his condemnatio
10、n of the street block. Berlages fine development in Amsterdam South is composed of streets and street blocks: for this and other shortcomings, Giedion dismisses Berlage as an architect of the previous century: .Berlages schemes reflect the central difficulty at that date: the inability to arrive at
11、new means of expression in the solutions offered for the problems peculiar to the times. In the 1902 plans particularly (and to some extent in the later version of 1915) we sense the struggle involved in Berlages attempt to break with the formulae of previous decades. (Giedion, 1954). In contrast Gi
12、edion, in his discussion of the Cite Industrielle, commends Garnier for his arrangement of lots at right-angles to the road and for his elimination of the street block: The closed blocks and light-wells of Hausmanns time are completely eliminated (Giedion, 1954). It is time to re-assess the value of
13、 the street and street block in the light of the new imperative of the green agenda for the city, and in particular in the light of the need to reduce atmospheric pollution caused by the burning of fossil fuels. The green agenda for the city renders obsolete the critique of the street and street blo
14、ck by the masters of the Modern movement in architecture. It is necessary to turn for inspiration, once again, to the great traditions of city building: to interpret those traditions in todays context in order to develop a new and enlightened vision for the sustainable city. In the design of street
15、blocks there are three broad sets of considerations. The first is the socio-economic function of the block; the second is the visual or physical role of the block in the city structure; and the final set of considerations is concerned with making the block work in terms of Figure 9.2 Project for a g
16、roup of ten-storey dwellings (Gropius, 1935) Figure 9.1 Project for a riverside or lakeside (Gropius, 1935) U R B A ND E S I G N :G R E E ND I M E N S I O N S 194 technology and includes considerations such as the lighting, ventilation and heating of the buildings which comprise the block. When form
17、 was considered the product of function and technology, then the street block varied in size according to function and to the limits set by technological feasibility. The result is all too obvious: cities with large blocks of single use disrupting the intricate network of public paths; a coarse-grai
18、ned city dying at night, a fearful place for citizens unprotected by the comforting envelope of a fast-moving car (Figures 9.3 and 9.4). Most urban functions, however, can be accommodated reasonably in urban street blocks of similar shape and form (Turner, 1992). Street blocks or insulae in historic
19、 towns dating back many centuries have been modified a number of times as they have changed ownership or use. The following paragraphs, while addressing function and technology, will place greater emphasis on the visual and structuring role of the street block in the city. If a reasonable size and f
20、orm for the street block can be determined from considerations of its structuring role within the urban fabric, then it is argued here that it will accommodate, with modification, most city needs. While the theory of sustainable development points clearly towards a mix of land uses in the city, the
21、quarter and the street block, neither the precise nature nor the degree of intricacy of land use mix is specified. Clearly, the placing of buildings designed for large-scale noxious, noisy or dangerous activities next to family homes would be unacceptable to both professional and citizen alike. More
22、 difficult is the decision about the juxtaposition of homes where peace and quiet may be the expectations of some with pubs, takeaways and other small-scale commercial activities which may cause noise, litter and other nuisance. Such activities in a city, however, add to its life and liveliness. To
23、what degree, therefore, should land uses be mixed in the city? In particular, should the street block itself be of mixed use? These two questions are part of the debate in sustainable development. Theories can only give part answers; an examination of developing practice will provide the evidence fo
24、r definitive answers. Clearly, there will be single-use street blocks in the city of the future; that is, street blocks given over to, or almost entirely to, residential, commercial, industrial or some other single land use. Where possible, large areas of the city devoted to such single use should,
25、however, be avoided. As a guide, a city quarter of 20000 to 100000 people should contain within its boundaries Figure 9.3 Broadmarsh Shopping Centre, Nottingham Figure 9.4 Victoria Shopping Centre, Nottingham T H EU R B A NS T R E E TB L O C K 195 a reasonable mix of city land uses. It should compri
26、se a mix of uses to include opportunities for work, education, leisure, shopping and governance in addition to residential areas. The quarter is a town within a town, and as such it should have a balance of land uses reflecting the balance in the city as a whole. It is the quarter and not the street
27、 block which is the main instrument for ensuring a balanced distribution of land uses throughout the city. The city street block, however, with great benefit for the environment, may house a mix of activities, including such uses as residential, shopping, office accommodation and a small nursery sch
28、ool. Many existing city centres would have remained safer and livelier places if the tradition of living over the shop had survived. Some city councils in Britain are indeed pursuing a policy which aims to bring unused accommodation over shops back into use as flats, and also the conversion into apa
29、rtments of former office blocks. It seems that in the sustainable city of the future there will be a range of city street blocks varying from single-use blocks to those of multi-use in varying proportions and with varying combinations of uses. The size of an ideal urban street block cannot be establ
30、ished any more precisely than the size of a quarter or neighbourhood. As a rough guide, Krier suggests that urban blocks should be: .as small in length and width as is typologically viable; they should form as many well defined streets and squares as possible in the form of a multi- directional hori
31、zontal pattern of urban spaces (Krier, 1984). The smallest street blocks are generally found in the centre of traditional cities. They represent a form of development which creates the maximum number of streets and therefore street frontages on a relatively small area: such a structure of street blo
32、cks maximizes commercial benefits. The high densities associated with this type of development stimulate intense cultural, social and economic activity the lifeblood of city culture. The typical ground floor in this type of central city development has many doors and openings. The traditional Europe
33、an town centre has a quality of permeability: Only places which are accessible to people can offer them choice. The extent to which an environment allows people a choice of access through it, from place to place, is therefore a key measure of its responsiveness (Bentley et al., 1985). The street in
34、the traditional centre facilitates distribution, in addition to its role in economic exchange and social intercourse. In contrast, large modern street blocks have a few guarded entrances, and most of the interchange takes place inside the building where internal corridors, private streets or splendi
35、d atria facilitate movement and distribution: the corridor replaces the street, which loses its primary function. The larger and more homogeneous the street block, the greater will be its power to destroy the social, economic and physical networks of the city. The large-scale, single- use, single-ow
36、nership street block is the instrument most influential in the decline of the city: its effect together with that of its partner, the motor car are among the real causes of the death of the great city. It may be difficult to be precise about the size of the ideal urban street block, but it is possib
37、le to eliminate the block which is too large. Such blocks covering extensive areas are out of scale in a democracy, where power is vested in the people and not with the board of a conglomerate or council of a university. Street blocks in the early industrial cities increased in size towards the peri
38、phery of the urban area where land values were low and U R B A ND E S I G N :G R E E ND I M E N S I O N S 196 where development could be expansive. As a city grew in both wealth and population, so too would its centre. The central city expanded and consequently land values increased at its former pe
39、riphery, resulting in development pressures and large, over-developed street blocks surrounded by fewer but usually wider roads. Building programmes increased in size throughout the twentieth century, with single owners or developers building large sections of the city. The large development in sing
40、le or corporate ownership, however, is not entirely recent as a phenomenon. The medieval castle or the cathedral and its ancillary buildings have, in the past, dominated the city. Where this has happened, such institutions have presented an alternative power structure independent of the city and its
41、 citizens. In this century these alternative sources of power have multiplied in the city. Large industrial complexes, hospitals, universities and extensive shopping malls are all common to most cities. These large-scale, single- ownership street blocks, or in some cases city districts, may be conve
42、nient for those who manage or own the establishment, but citizen rights are not paramount: this is private property, and those with legal possession have great autonomy within their ownership boundary. There seems, however, no reason why, for example, a city university cannot be designed to occupy s
43、mall-scale city street blocks with buildings designed specifically for this purpose. A good example of such development is Oxford University with its rich mix of town and gown (Figures 9.5 and 9.6). The University of Liverpool, in contrast, followed a modernist approach to planning, destroying commu
44、nities, the street pattern and also the rich grain of small-scale urban street blocks. In place of the rich nineteenth century urban structure there is a large district of the city which dies when students leave at night for the halls of residence, and atrophies almost completely during vacation whe
45、n they leave the campus for home (Figures 9.7 and 9.8). The idea of the city as a growing whole led Alexander to postulate a number of rules to achieve organic growth the results of which he much admires in traditional cities such as Venice (Figures 9.9 and 9.10). One of these rules of organic growt
46、h is that growth should be piecemeal: .furthermore that the idea of piecemeal growth be specified exactly enough so that we can guarantee a mixed flow of small, medium, and large projects in about equal quantities (Figure 9.11). In detail, Alexander specifies that no single increment should be too l
47、arge Figure 9.5 Oxford High Street. (Photograph by Bridie Neville) T H EU R B A NS T R E E TB L O C K 197 and that: There are equal numbers of large, medium and small projects (Alexander et al., 1987). The figure that Alexander places on the upper limit for projects based presumably on the North Ame
48、rican experience is 100000 square feet. This figure represents a four-storey building block, without light wells, of just under one acre in extent. The upper limits set by Alexander may be too high for the British context, where street blocks traditionally tend to be smaller than those in the USA. S
49、ustainable development suggests an upper limit for development of three to four 9.6 Figure 9.6 The Radcliffe Camera, Oxford Figure 9.7 University Buildings, Abercrombie Square, Liverpool 9.7 9.8 Figure 9.8 University of Liverpool, Bedford Street North Figure 9.9 Rialto Bridge, Venice 9.9 U R B A ND E S I G N :G R E E ND I M E N S I O N S 198 storeys, which also points to development units of smaller scale than those envisaged by Alexander. There seems to be a strong case for breaking down into discrete units of single street blocks those large-sca