Micro- and Macro-structures of a More Sustainable City
3.6 A City Form Based on Transport Systems
The inclusion of a variety of functional, social, economic and environmental criteria in the evaluation of urban models of different forms and structures strengthens the argument for a composite city form. In view of the rather poor performance of the core city in some aspects, one cannot help forming the impression that the search for one generally valid form of sustainable city, e.g.
the compact city, might be in vain and perhaps a little naive. Furthermore, knowing that the major task is not the design of a new and ‘ideal’ city but the redesign of existing cities, one needs to take into consideration that each existing city is unique in its physical structure and form, land-use pattern, activities, socio-economic conditions, history, topography and micro-climate and so on, and there may simply have to be different planning and design approaches for different cities in order for them to become more sustainable. But to return to the comparison of city models, there is another issue which greatly influences city form; it has already been touched upon but needs further exploration.
Walking as an alternative means of transport provides access to services and facilities as long as these are located within 10 minutes’ walk from one’s front door. Because of the limited population that can live within a 600 m radius, local facilities can be expected to provide only for the most essential daily needs.
Mobility over and above walking distance is therefore essential for today’s urban society, which relies on ever more specific uses and specialised provisions which do not necessar-ily depend on central locations (see Farthing et al., 1996, p. 182; Breheny, 1992, pp. 138–59). Recreational facilities or workplaces, for example, are provided in increasing varieties and in a large number of different locations. Access to these locations offers a choice of different qualities and types of services and facilities in the city. Transport is therefore of the utmost importance for the quality of urban life. City forms that facilitate transport, specifically those that support public transport, are therefore more appropriate than city forms that do not. One may therefore conclude that, in terms of mobility and transport, the most efficient city form is the one that follows the transport network, but not all forms of transport networks are equally efficient.
The star, the linear and the regional city develop along transport routes. In the star formation the routes converge at a central point, the city centre. Experience
with city development in the past shows that with growing size of the city the more central stretches of the transport lines will become more and more congested as long as the city relies on one single core. The polycentric net does not have converging traffic routes in a single core but, like Calthorpe’s TODs along a network of ‘trunk lines and feeder bus routes’ (Calthorpe, 1993, p. 62), a number of lines crossing at a number of nodes. In this configuration transport is dispersed rather than concentrated, enabling reasonably equal access to all urban areas, and the danger of traffic congestion is relatively small as long as none of the nodes at a transport interchange grows too large. This means that a transport network will work best if it does not rely on a single core, i.e. if the city is multi- nucleated.
The replacement of the radial and circumferential network of transport in the traditional city by a pattern based on a large-scale gridiron plan was suggested by traffic engineers and planners in the early 1960s because the grid serves all areas of a city or metropolitan area rather than a single point at the core of a traditional centralised city (Fisher, 1962, p. 58). At a time when in Glasgow the transport planners established a radial and circumferential transport structure for a city which actually grew more linearly than radially, city planners elsewhere had already recognised that such a structure will eventually lead to congestion in the core and inner ring area (Manners, 1970, pp. 232–4). The Chicago Area Transportation Plan of 1962, for instance, shows the old radial and circumferential transport network to be expanded into, and to a degree superseded by, a grid pattern (Chicago Area Transportation Plan, 1992, p. 112).
By now the fact that ring roads do not solve traffic problems but create more problems is a daily experience in many cities.
3–30. The regional city with transport grid, primary and secondary centres
Development along public transport lines, and specifically at transport stops, allows easy access to public transport systems as long as development is shallow, i.e. not more than 600 m away from public transport lines and stops.
This leads to an urban structure with high-density mixed-use cores of development forming primary centres at crossing points of a public transport
grid; high-density mixed-use nodes of development at transport stops of a single line form secondary centres. This structure seems identical with Calthorpe’s pattern of TODs, except that the primary and secondary centres can be expected to be much larger than neighbourhoods and that access to a hierarchy of centres is provided by a hierarchy of public transport (Fig. 3.30).
3–31. Different degrees of compactness of the regional city
Without going into the micro-scale structure of components of the city, I still
need to discuss the ‘calibration’ of the net, not in terms of densities but in terms of the distances between lines of different transport systems, which will undoubtedly influence their accessibility on the one hand and their viability on the other. Regarding densities, the city model comparison has shown that fragmentation of urban fabric may not necessarily generate low overall population densities as long as the most compact of city models, the core city, also includes a certain amount of open land, which it requires for social, environmental and ecological reasons. A polycentric net, therefore, may not necessarily have to be unconfined, of low density and loosely structured; in places it may actually be rather compact, in other places less so, depending on the amount of open land integrated into the structure. The net may be loosely structured, with larger distances between development components such as core
‘villages’ or core ‘towns’, i.e. with a larger proportion of agricultural and forestry land, in more rural and country town areas, and it may be more compact, i.e. include less open land, in city and metropolitan areas (Fig. 3.31).
Even the structure of a large city or metropolitan area may form a more compact net in some parts, e.g. in its central area, and a less compact net in others, e.g. at its edges.