This thesis has investigated the structure of transport networks, and demonstrated how these may be used to structure urban areas. It has made explicit a variety of aspects of urban structure, and suggested ways of designing urban structure. By understanding better the nature of this urban structure, it should be possible to improve the contribution of transport provision to urban design. Overall, the thesis provides a theoretical foundation to urban structure that may be used to underpin contemporary movements towards sustainable mobility and neo-traditional urbanism.
The rhetoric of contemporary urbanism expresses the aspirations to remove vaguely articulated 'bad hierarchy' and 'standardized layouts' and replace these with vaguely articulated 'good hierarchy' and 'clear, coherent layouts'. This thesis goes beyond this rhetoric and scrutinizes the first principles used to inform modernist planning and engineering, as exemplified by the deconstruction of Traffic in Towns' approach to road hierarchy.
The approach is therefore evolutionary rather than revolutionary, in that it builds on those principles, based on underlying relationships between urban structural properties, to provide a robust theoretical basis for contemporary urbanism. Rather than overthrowing the 'highway hegemony' implicated for its part in 'disurban creation', the thesis in a sense enlarges awareness of the solution space of design possibilities. Within this, the conventional approaches of tributary layouts of distributor roads may still be found, albeit as examples of simple, traffic-flow oriented solutions which might be useful in specialized circumstances, but which are no longer considered desirable for blanket application as the basis for forming urban structure. The approach is therefore both compatible with existing conventions, while paving the way towards meeting contemporary asbdb6c10ac8d20fa6b687bb45a101acdfpirations.
This concluding chapter reflects on significant outcomes of the thesis and analyses some of the main component outcomes drawn from across the thesis as a whole, following which it is possible to draw conclusions for onward application of the research. Finally, some concluding reflections on the thesis topic are provided.
11.1 Key thesis outcomes
This research had addressed the design debate concerning how transport provision, in the form of routes and street patterns, may be used to form the urban structure of settlements. This has involved considering both the layout concerns of transport engineers and the broader urban concerns of urban designers and planners. The significance of urban structure as a topic of research is not least that it is at once an overlapping concern (the source of occasional conflict between different design professions) and at the same time something of a void - unregarded and unresolved.
A specific gap encountered is the inadequate specification of desirable properties of urban structure, and the absence of guidance for its composition. Where overall patterns are advocated, these are often ambiguously specified. And where distinct 'preferred' and 'discouraged' patterns are offered, these seem inadequate for expressing the full breadth (and limits) of the implied solution space.
This issue has been addressed and resolved. Firstly, means of explicitly describing structure in a useful way are offered. These strike a balance between simplicity and complexity. On the one hand, they are intended to be readily calculable, based on simple, recognizable topological properties. On the other hand, they also must be sophisticated enough to detect the subtleties of heterogeneous forms, since a simple division into 'grid', 'radial' and 'linear' patterns cannot comfortably accommodate the majority of real patterns. Ways of describing networks in terms of their elemental structural properties have been successfully developed. Structural fPT3HO8AaG6oQcgZ/QvTypTEwe5Tb0ifsVs/8sIfIjY=description is also most useful if it can relate meaningfully to the way that networks are designed, and the way that they are used.
The route-structural approach deals directly with structurafPT3HO8AaG6oQcgZ/QvTypTEwe5Tb0ifsVs/8sIfIjY=l elements - routes and junctions - that networks are built with. The structural role that routes play in a network will have some influence on how they are used, and this route-structural approach provides a distinction of different structural roles that may then be equated with actual or potential function.
The route-structural properties can thus help to 'type' networks - for example, more or less connective networks - as well as individual routes - such as connector streets. This is important, since these are precisely what are being called for by contemporary urbanists.
By making more explicit the relationships between structure, hierarchy and route function (transport mode and frontage function) it is possible to set up a robust system where these elements are mutually reinforcing. This goes beyond nominally placing the pedestrian at the 'top of the hierarchy', while all the time 'car orientation' continues to be built into the route structure.
The detailed investigation of the structure of networks and hierarchies has therefore allowed confusion between 'tree-like' hierarchies and 'tree-like' patterns to be cleared up, paving the way for more purposeful tailoring of networks to hierarchies, and vice versa.
Effectively, this research has shown that it is possible to account for the structure of networks and hierarchies, so that urban designers and planners may then 'point to' which ones they regard as possessing desired properties, which had hitherto been ambiguously specified.
The significance of this lies in the fact that contemporary calls for neo-traditional approaches, and reversion to traditional network structures, and creation of new kinds of hierarchy (unspecified, except that they are not conventional road hierarchies), have had little theoretical support. This is in contrast to the realm of conventional road hierarchy and structure, which has a robust theoretical logic and justification. To the extent that the post-Buchanan modernist approach is indeed a robust and consistent approach, it was never going to be satisfactory to muddy the waters by habitually 'compromising' its supposedly ideal standards in the face of messy reality, 'tacking on' allowance for crossroads, or 'inverting' the (still-linear) hierarchy in favor of the pedestrian, if it is desired to achieve a robust and coherent philosophy of design that could rival or supplant the modernist approach. This research has therefore provided theoretical support to how neo-traditional patterns and hierarchies might be structured.
As urbanists seek to reclaim the territory of street design, there may be a temptation to lay waste to the existing theoretical structures, but this should be resisted unless there is something adequate to put in their place. The fact that this thesis' approach builds on the conventional approach means we should avoid tRvYOUik64ZDVDYfMjdCiVw==he danger of throwing the 'baby' of hard-earned empirical research and engineering practice out with the 'bathwater' of unimaginative design solutions and defensive professional dogma.
While paving the way for more traditional forms such as high streets and crossroads, the recognition of the role of hierarchy means there is still a means of relating configuration and constitution, whether understood in terms of 'natural' or 'emergent' hierarchies, or sensitively constructed artificial ones. This means that the designer can choose to keep some relationships fixed (e.g., the hierarchical access constraint for vehicles), while allowing degrees of freedom in others (e.g., mixed-mode streets, or connective patterns).
This avoids simply releasing all constraints simultaneously, which might otherwise court the 'chaos and carnage' feared by engineers.
Overall, the thesis has provided a view as to how one might tackle the design of cities by way of an approach that is both organic and rational, based on local constitutional rules, rather than off-the-peg, pattern-book solutions. This approach is flexible enough to accommodate both conventional and neo-traditional tendencies, and theoretically it could apply or be adapted to any movement structure.
Part of the problem with the Buchanan Report was that it became associated with the modernist style of the 'solutions' it appeared to offer. A similar situation potentially arises here, where this thesis is proposing a constitutional approach - this time in the context of modes of design suitable for the 'organic' creation of 'traditional' style layouts. Nevertheless, this should not restrict the approach to creating quasi-organic or quasi-traditional patterns. While having empathy with these patterns, it is no more restricted to generating these than Buchanan's constitutional approach required conversion of high streets either to expressways or backwater 'twigs'.
In the end, the research provides a mor9cfe75a4576bef6403c660d51ae8b45be detailed 'map' of the solution space, which shows features which might be of interest to urban designers and planners. For example, 'characteristic' network structure, or alternatives to 'tributary' hierarchies, have been intuitively sought - and perhaps sometimes stumbled upon - by urbanists, but the routes to reach them have not n40e07cf61eabfe2a28cbfa8db6d6d402ecessarily been clear. This thesis provides a map and some signposting, although in the end, the decision as to which route to go down, in pursuit of which destination, is left to the individual.
Similarly, while the thesis' integrated design approach could be put to immediate use, by tailoring to fit with existing UK design guidance, it is not limited in applicability to a particular national context or stylistic preference. It is a conceptual system that - like the original concept of 'hierarchy' - could be applied in practice in a variety of countries, and is flexible enough that it may be used by New Urbanists and traditional engineers alike.
Indeed, the 'battle for design territory' might not, after all, be resolved simply by engineers throwing away the rule-book and acceding to the wishes of the planners, but by both taking forward the most appropriate approaches of both design traditions what are, in the end, commonly held aspirations towards viable urbanity.
11.2 Synthesis of Themes
The preceding discussion has dealt with the main outcomes of the thesis. This section reviews and synthesizes a series of individual components which cut across a variety of chapters.
11.2.1 Distinction of concepts and properties
The distinction of urban structure, as constituted by transport networks, as separate from urban form and urban fabric can be regarded as a starting point to understanding how cities may be put together.
The distinction between three aspects of structure or structuring - constitution (of route typology and hierarchy), configuration (of network topology) and composition (of absolute layout) - also allows clearer discussion and debate on differences in proposed layouts and structures. Individually, these concepts have appeared before; the added value here is in the consideration of the three together, as distinct but linked entities.
This allows the separate consideration of desirable or undesirable hierarchical systems, preferred and discouraged configurations and preferred or discouraged layouts. It short circuits the unhelpful polarization in an already entrenched debate about 'good' (or 'bad') grids and 'bad' (or 'good') cul-de-sac. This should allow more variety, since it allows hybrid layouts which combine (the benefits of) rectilinear urban blocks with pedestrian connectivity and tributary vehicular layouts.
The thesis has also suggested formal conventions for expressing a variety of structural properties such as connectivity, complexity and arterially in route-structural terms.
Overall, the variety of concepts and properties crystallized and developed in the thesis, which may be regarded as contributing to the understanding of urban structure, is demonstrated in the Glossary.
11.2.2 Typologies
A typology can be a useful means of dividing up a continuous spectrum into recognizable graduations, or labeling discrete permutations of independent variables.
The thesis has generated and made use of a variety of typologies, including not only types of recognizable street pattern, but deeper patterns of structuring or design approach.
These typologies to varying extents describe, analyze and explain structure.
The most basic attempt to purposely apply labels (in a reasonably systematic way) to observed street patterns. Those of Chapters 7 and 8 are in some ways a by-product of the attempt to analyze structure: in the former case, to establish what kind of structure is valid for analyzing, and in the latter case almost as a by-product of calibrating the structural properties analyzed.
Meanwhile, the most to attempt to explain structure. The building-structural analogy explains four broad types based on influences reflecting various functional priorities. The distinctions of Chapter 9 draw attention to the question of the extent to which patterns are deterministic in the first place. In the case of the genetic paradigm, this does not really classify actual structures, rather the method of their conception, though it could be used to differentiate more or less 'planned' towns, or classify town plans.
There are some broad correlations between types, from which we could suggest examples.
There is not an exact correspondence between types, and this is as it should be, since the characterizations are describing different things. POSTMODERN and CHARACTERISTIC forms are difficult to pin down out of their context since they are essentially eclectic or undirected towards specific formations. There is only one case of exact correlation, or rather nesting, where ABCD is derived directly from a fuller set of 10 permutations.
Nevertheless, it is possible to discern some cross-currents. In some cases the typologies arise out of a need to recognize what is being described: in this case, mostly it is 'vertebrate' or route-based structures, which provide the foundation for the analysis. There is also a gradient from consideration of 'anthropic' structures - deliberately conceived types such as the CLASSICAL, or the GRIDHIERARCHICAL, or the TRIBUTARY - to the recognition of 'entropic' structures such as the ORGANIC and CHARACTERISTIC types. Finally, structures arising from footprint.
These combinations are not named, to avoid creating the impression these are necessarily typical, congruent or inevitable. Additionally, the underlying component typologies are to some extent low resolution, not always clear-cut nor congruent. Creating new meta-types based on permutations of these might spuriously give the impression of a high-resolution typology.
Formation seem to equate with A-type characteristic patterns, while modem C-type and D-type are almost certainly dominated by route propagation.
The typologies in some cases open up new perspectives, in other cases they expand existing categorizations or graduate existing polarities. For example, the building-structural analogy expands on the traditional/modem bimodality; the classification by relative connectivity graduates the tributary- griddy spectrum; those of Chapter 9 help to distinguish between planned and unplanned, regular and irregular structures, while Chapter 10 explores (or explodes) the mechanistic organic opposition.
11.2.3 Analytic and Synthetic Tools
If the typologies above are conceptual tools, the thesis has also generated some practical tools that may be used in the design process. Some of these are analytic tools, some are synthetic tools, but both can contribute to the overall process of design.
These tools have been discussed in detail in the relevant chapters, and most have already been summarized in Table 10.8. Some of these tools are expansions or developments of existing items (e.g., the hierarchical types or constitutional archetype have direct antecedents) while others, such as the netgram and routegram, are new departures. While these fit into the integrated design approach proposed in this thesis, some of the tools could be usefully be applied independently in other contexts. For example, the netgram could be used to distinguish structures other than those representing transport networks.
11.2.4 Desired features of networks
We saw in Chapter 4 that many of the desired or advocated qualities of urban structure were unclear or ambiguous. This research has offered some explicit interpretations which could help resolve these ambiguities:
a 'connective network' might be one with Qc of 0.375 or more;
a 'connector street' might be one with qc of around 0.4 or more and q of about 0.25 to 0.4;
a 'coherent network' might be one with internal consistency of relative connectivity and complexity;
a 'clear hierarchy' suggests one in which recognizable route types connect to each other in consistent ways. Possible examples would include:
(1) a hierarchy of types where route type was pegged to structural role (Ql, Qc, Qd);
(2) a constitution with clear explicit rules for arteriality and access constraint (for different modes, as appropriate).
a 'less rigid' hierarchical structure might then be one with a non-linear structure, and/or one which relaxes the access constraint;
the type of hierarchy often deemed desirable by urban planners and designers may also be identified as a 'spatial' rather than 'structural' hierarchy, ie, exhibiting differentiation of route type, but not necessarily arteriality. This corresponds with the 'mosaic' constitutional type or the linear horizontal case.
The above suggestions could be specified to any desired level of precision, commensurate with the intentions of their advocates. The explicit resolution of these specific points serves to illustrate that the structural investigations, which have involved substantial theoretical deliberations, can deliver clear, concise and useable results that resolve outstanding contemporary concerns.
11.2.5 Approaches to Design
This thesis has generated a design solution space which admits a wide variety of possibilities for urban structure and structuring. These include pursuit of neo-traditional design by pattern replication, neo-organic design by constitutional program (i.e., governed by hierarchical connections), as well as conventional design using both tributary hierarchies and tree-like patterns.
The above represent broad tendencies; in reality there would be a finely differentiated spectrum of approaches to design, based on different constitutional strategies and scales of intervention (spatial and temporal). It is suggested that where it is desired to emulate organic, traditional structures, constitution-driven approach may be sufficient.
The street can form a key elemental unit of this structural approach to urban creation. The street can be seen as a microcosm of urban integration: in uniting route, public space and built frontages, it provides a robust unit of generation from which integrated urbanity may be built. In this sense, if the elemental unit is integrated, it should be possible to ensure integrated urbanity overall.
The design process envisaged in the thesis concentrates on theoretical relationships between different components of design, such as network structure, hierarchy and route function. The theoretical compatibility or potential for intermeshing with conventional highway regulations and land use planning and building controls has been noted, though the practical details of doing this have not been worked through as part of this research. To operationalise this would involve not only consideration of what kinds of changes would be needed, but how this transformation would take place and who would effect it.
11.2.6 Explanations of Urban Structure
In seeking to understand the kinds of urban structure and patterns that urban designers desire, the research has investigated a variety of urban structures, and formative influences. In fact, in a broad perspective we can see how the structure of cities can be seen as a series of more or less deterministic layers.
Seen this way, we see that the design philosophy is only the tip of the iceberg in terms of determining what shapes we see on the ground. Thus, architectural fashions will come and go, but these are embedded in a wider cultural and societal context, which both moderates demand for the designer's products and limits possible solutions - even if only by the inertia of tradition or habit. The societal context may also moderate or prioritize 'functional' requirements which the designer may otherwise take for granted. For example, the prioritizing of transport efficiency in the era of modernism placed higher value on speedy movement (with attendant safety considerations) over the preservation of traditional fabric, displacing homes and uprooting communities in the interests of progress. Today, sustainability seems to be the most insistent priority.
Within the context of transport, we have seen the co-evolution of transport technology and urban structures. The transport structures are heavily influenced by the basic attributes of the modes themselves. This fundamentally boils down to two basic polarities: the attributes of human versus motorized locomotion, and individual versus collective transport. This perspective in a sense strips away the conventional conceptual baggage of car versus anti-car, private versus public and freight versus passenger transport. As far as urban structure is concerned, the basics appear to be range and penetration. Just as buildings have been designed using the reach of the human body as the basic unit of space, we can extend this to include the additional 'reach' provided by transport, to apply to a whole city.
Ultimately, the very structural solutions that may be available for selection are a factor: whatever other human factors are oveebf0efc67117aef1143b4da1bf5ee862rlain, at the most fundamental level of all are the basic laws of geometry and probability. Some layouts are more likely than others simply because there are more ways of arranging a given sets of component parts than others.
Human intervention can act at a variety of levels to alter this basic probability, by ordering in a more regular pattern than would otherwise be likely, or even to contrive more complex patterns or deliberately replicate irregular 'unplanned' patterns, for whatever functional purpose, be it transport, or a deliberate expression of culture. But, in the absence of system-wide intervention, the city structure will arrive at a certain kind of characteristic structure which appears irregular but which demonstrates a quite specific range of structural attributes. In a sense this characteristic form is the most 'deterministic', from the point of view of the city, as it were, left to its own devices.
The implications of all this is that patterns characteristically found in traditional and 'unplanned' settlements do have a structural logic: while they may be irregular, they are not amorphous. Neo-traditional designers therefore have the choice of replicating these recognizable patterns, or replicating the kinds of programs or processes that created them.
11.3 Research application
The research in this thesis may be applied to design practice, as already discussed in Chapter 10, and also can lend itself to further research and development.
This section summarizes the possibilities for application to further research, followed by an outlook on possible application to design practice.
11.3.1 Application to Further Research and Development
The five principal areas for further research and development identified in Figure 11.2, (1) to (5), are now discussed in turn.
(1) Methodological development would include the exploration of alternative conventions within the methods developed within the thesis; the development of new methods; and the comparison and correlation between the methods in this thesis and other areas.
Alternative conventions could be explored in the case of route structure analysis (RSA). These could include (1) Testing the effects of allowing two routes to retain continuity across an intersection; (2) Varying the datum from which 'depth' is measured - for example, from a point, a line or external connectivity; (3) Exploring the use of non-junction nodes to increase the continuity of individual routes as a proxy for metric length.
The various analytic tools developed could also be applied in slightly different ways. It could be possible to develop 'homogeneity analysis', where areas homogeneous in some structural sense would be mapped, creating a mosaic of different shaped and sized pockets across an urban area. These could homogeneous in terms of their ABCD typology (which inherently rely on homogeneity for their definition), but could also be applied to areas of similar regularity or complexity, revealing, for example, pockets of 'plannedness' within zones of 'unplannedness', or vice versa.
The various concepts, typologies and tools developed within the thesis could be compared and correlated with concepts and tools in other methodological approaches or other fields. For example, structural description could be systematically evaluated against the existing methods outlined in section 7.1 (e.g., conventional urban morphological or transport network descriptors), and the circumstances in which each was most appropriate could be deduced. Additionally, CB3WThV/Nlup4shwYe25FTfdn5pf1CKNwp8lpNtucO0=comparisons with hierarchical or structural concepts in other fields could be made, e.g., with organizational hierarchies and social network structures.
(2) Theoretical exploration would include the development of theoretical concepts with which to describe and explain structural phenomena, and a fuller mapping of the solution space of structures, in terms of the netgram, routegram and differentiation plots. The theoretical exploration of the solution space is represented diagrammatically in Figure 11.3.
Theoretical concepts to be developed could include quantification of the concepts of entropy and coherence, and other measures of structural variance and probability. This could also establish how far the probabilistic geometry of structure affects observed patterns. For example, this could investigate in more detail of effects of network size (up to settlement scale) on complexity and regularity, and the nature of the large-scale, emergent patterns thus formed.
Mapping of the solution space would include both the identification of patterns (Figure 11.3 :a) and the identification of theoretical zones in the route gram and netgram (b). The latter could include, for example, (1) zones within which all T-junction networks lie; (2) positions where all networks of given maximum depth lie; (3) positions of networks of a given regularity or complexity (representing 'plannedness' or 'unplannedness'), as plotted on the netgram.
It would also involve plotting trajectories of growth of structures over time (Figure 11 .3:c), and correlating these with possible programs that would generate these (d).
In general these analytic parts of the research invite greater application of computers, not only in automating the representation and analysis of structures and their relationships, but in generating structures and simulating their growth. In particular, the enumeration of 'all possible structures' for a given rule system would be particularly speeded up by automatic computer processing, to explore the probabilistic surface of the solution space in more detail. The solution space itself could be represented more fully in three dimensions, where each vertical layer could represent networks of the same size.
Overall, a variety of different programs for growth could be developed. Ultimately, the modelling of all three types of structural formation (routes, plots and building footprints) would be included, which could therefore also take account of models of land ownership and use and building size and shape. The link between these theoretical considerations and actual settlements must then be completed. This would consider causal relationships that give rise to the structural formations under consideration. This would include the detailed observation of processes - including political and practical as well as design-theoretical - which give rise to the forms. This can be done from a geographical and historic perspectives, in which the actual settlements in physical space can be related to their theoretical counterparts in geometric space.
(3) Geographical application refers here to the spatial analysis of actual settlements. This involves analyzing and comparing (a) different settlements, and (b) different parts of settlements (e.g., core versus periphery). This would be done by mapping these settlement structures to different points in the theoretical solution space, hence describing them in terms of properties such as compositional shape, connectivity, regularity and complexity, which may then be related to external influences (d). This analysis could include a historical dimension, in application to structures at past dates, or parts of a contemporary settlement built at different times.
Overall, it would be possible to 'type' settlements systematically by their structural properties: a 'morphographic taxonomy' could be based on combinations of variables such as connectivity and complexity, related to size. A further possibility would be to create a 'morphogenetic taxonomy' of settlements based on how closely their structures are 'related' with respect to divergence from common 'structural origin' (i.e., development from common primitive shapes to increasingly diverse structures). This is related to the expanding solution space of all possible structures.
(4) Historical application here refers to the systematic tracing of the development of settlement growth over time. This would involve plotting the trajectory of a settlement structure through the solution space. The changing properties (or connectivity, complexity, etc) may then be assessed with respect to external societal influences. The possible correlation between these external influences and discernible changes in the programs could also be investigated. Where historical correlation between known examples of planned interventions and planned quarters of cities is known, these might be abstracted from the whole urban area to leave what are deduced to be 'unplanned' areas. Hence, it is possible to deduce rules or programs of structural formation for these
'unplanned' cases. In the other direction, the identification of different kinds of structure could help structure to explain or reveal historical processes. For example, heterogeneity analysis might be used as a 'forensic tool' to unearth hitherto hidden plan order in urban structure, hence assisting with conventional morphological investigation.
(5) Functional application here refers to the direct application to the transport and urban planning context, regarding the functional and performance of different kinds of urban structure.
Further research can assist with the debate over optimal structures for different purposes, and provide an empirical basis for the supposed linkages between urban structure and modal and urban function. This would entail the detailed correlation of structural properties of routes and networks with traffic and travel behavior and urban function. For example:
(1) Investigation of possible 'modal optimality' functions (ie, relative to Ql, Qc and Qd);
(2) Patterns of land use and frontage activity associated with different route types;
(3) Possible suitability for the 'labyrinthine' constitution for vehicular networks;
(4) Investigation of circumstances in which greater use of 4-way and 5-way junctions may be made;
(5) Testing differences between structures of dedicated modal networks;
(6) Testing differences between macro structure and micro structure.
In doing so, this would also enable the testing of the supposedly desired forms, which have been taken as given, from contemporary literature. For example, we can confirm the extent to which 'connective networks' and 'connector streets' are indeed compatible with their desired roles.
At the broadest level, the existence of definable, recognizable parameters expressing urban structure allows the very concept of 'urban structure' to be included with other urban fouyyCwCjJlMWGtNfmW8/cGQ==rm variables (eg, density, settlement size) in testing for sustainability and other indicators of urban functionality and desirability.
In the end, this empirical testing will allow more precise targeting in the design process, and hence contribute to the refinement of the design components for practical application.
11.3.2 Application to Practice
Overall, implications for design and suggested approaches to design have been discussed in Chapter 10. This section draws out some specific possibilities for onward application.
Application of individual outputs. Without any significant alteration to current design approaches, individual findings or suggestions from this research could be put directly to use. For example, the suggested structural definitions of connective networks and connector streets could simply be appended to existing expressions of advocacy for these forms, without any wider application of route structure analysis or reconciliation with conventional highway engineering approaches. Similarly, the explicit diagrammatic representation of allowable route types and their connections (e.g., the connectivity table) might be applied to conventional highway engineering approaches without making any changes to their content.
Application of the Integrated Design Framework. We have already seen that it is possible to combine the individual components into an Integrated Design Framework. Possible approaches within this have been suggested. The recommended path which uses the full framework would imply a series of changes, or stages of implementation.
1. Mixed mode hierarchy. This involves the linking of route type to transport mode and frontage function, and implies explicit and independent consideration for pedestrians and public transport. The incorporation of frontage function would also effect the institutional rehabilitation of the street, and represent a first stage in integrating transport considerations with land use/built form.
2. Constitutional type. This implies the separation of different constitutional organizations for different modes, with explicit promotion of arteriality for public transport networks, and safeguarding accessibility for pedestrians and pedestrian access to public transport. A possible departure would be to abandon arteriality for vehicular networks, if the labyrinthine constitution is found to be acceptable.
3. Junction connectivity. This implies looking at circumstances in which greater use of more 4-way and 5-way junctions, to promote overall network connectivity. This element would require careful argument in order to overcome conventional dissuasion and disuse of these junction types. This thesis has only outlined the theoretical advantages of these from one point of view, that of urban structure. More work would be needed to reconcile these with other areas of concern. The application of this element would allow new creativity in network structure and would help to support the full range of structural roles of routes envisaged.
O6Arsek1PYe8ECk6kw3R2TsVPwYh5Z/ZgDY5bSmMXE8=4. Route structure analysis (RSA). Adoption of the full framework would imply adoption of route structure analysis for checking route and network properties. Further, it would imply acknowledgement of the relationship between route types and their structural roles. The relevant extent of this relationship would be supported by research into 'modal fit' and structural role. The adoption of a more permissive use of 4-way junctions would pave the way for the inclusion of 'connector streets' and 'cross connectors' in the route typology, as well as generating networks of greater typological diversity and complexity.
Towards an Integrated Urban Design Framework. The approach just outlined would form an acceptable means of designing a street system. However, a further stage would be to 'flesh out' the framework, integrating street specifications with local codes for frontage types, land uses and built form. These latter components could be specified in their own right and then combined in the constitutional archetype.
This would ultimately imply a more ambitious project, and integration with the disciplines of urban planning, urban design and architecture. A fully integrated approach would imply not only inter-professional and institutional compatibility, but complementarities with a wider range of urban and sustainability objectives, and accommodation within the wider regulatory context (e.g., statutory planning processes).
The ultimate implications for the planning system and design professions are not pursued in this thesis. Nevertheless, the design approach and conceptual tools proposed herein have the potential to bridge between transport and urban design professions, as well as potentially integrating a degree of local community control within the planning system. The result could be the replacement of 'monolithic modernism' with a more flexible, site-sensitive, organic approach to urban planning and design.
11.4 Concluding discussion
The romantic mode is primarily inspirational, imaginative, creative, vw6k6KlHlEAL83siO9ZgT+yGs0+CkvwFQGSWYX5ahsU=intuitive. Feelings rather than facts predominate... The classic mode, by contrast, proceeds by reason and by laws - which are themselves underlying forms of thought and behavior, there is a classic aesthetic which romantics often miss because of its subtlety.
At the outset of this research, transport provision was seen to be part of the urban problem. Highway engineering approaches seemed rigid and mechanistic, and needed to be changed. The engineer seemed more in danger of being buried than praised. If only transport provision could have some more thoughtful, creative treatment, then perhaps a more harmonious, livable environment would result.
The 'design debate', embodying the search formP3tNYs3JW1QNOBXeRwtoM/h6kIC9CwH6/k7i2CpuCU= a more integrative approach to transport and urban design, was the stimulus to the research. It became clear that the key unresolved concern was not so much avoiding urban destruction, but avoiding disurban creation. This effectively focused the research on the issue of transport as urban structure, and the 'nature of urban structure' became a second strand that would support the resolution of the first, the design debate.
It seems well enough established that designers should resist thinking of cities as 'trees', and that traditional cities possess a kind of organized complexity that seems to be a prerequisite for urban vitality. The investigation of the second strand, the nature of urban structure, suggested that if one aspires to recreating traditional urbanity then perhaps traditional bottom-up processes may be more effective than simply replicating patterns in the manner of top-down master-planning.
This gives rise to the possibility that a kind of 'constitutional' system of structural generation already used by the highway engineering tradition may turn out to be capable of, if not preferable for, generating the elusive emergent properties of coherence and organized complexity, which are desired or appreciated by 'urbanists' of whatever profession. Perhaps surprisingly, then, the engineer may already have the rational foundations for generating urban structure, from which a variety of urban design creations may arise.
The approach of this thesis has in some senses built on the principles in the Buchanan Report, but has evolved into a more complex system. This demonstrates a broader 'solution space' to accord with today's needs. This enlarged 'atlas of patterns' would therefore accommodate the present, functional reality of London's Fitzrovia, with its balance of transport modes, mix of uses, and a combination of accessibility and environmental quality which contribute to its urban vitality.
As it has turned out, the thesis has made use of a certain degree of biological imagery and metaphor to express certain aspects of urban structure and urban creation. This organic slant was not originally sought out; rather it impressed itself repeatedly from a variety of sources, and in the end became too useful to suppress. An 'organic solution' to urban creation was not particularly anticipated as being part of the resolution of the thesis, at the outset of the research. Yet, CagtnLTTpUY0LsZu0x/Ceg==the biological theme seems to have emerged almost as a ghostly third strand which seems to tie in the structure of urban design with the design of urban structure.
The significance of this is in the way in which processes of growth relate to structural form, and the way that a coherent, complex whole can arise from the interaction of simple elements.
This is in contrast to the grand design of the town planner as artist, and the city plan as a canvas. Especially, it is in contrast to the approach of 'monolithic modernism' which took the city as a complete arte fact, a designable object - even if also a 'living organism'. This combination of modernist abstraction and organic creation may be illustrated with reference to Picasso's image of the bull.
By the end of the series, the bull has 'de-evolved' to its bare, abstract 'essence', which is a superficially recognizable image of a bull. This final image recalls the low resolution
compositional abstraction of city layout often used in modernist planning.
However, though such images may be visually appealing, or appear superficially organic, they do not necessarily represent the best starting point for design. We have seen how a city is in many respects more like a living entity than a work of art; it is a creature of structural intricacy and emergent complexity.
In other words, if we were going to try to create a bull, as it were, we should not try to start with Picasso's 'outline plan' of the bull. Rather, we should seek an appreciation of the elemental parts, of the workings of 'muscle and bone', if not some sort of organic code.
Such a solution is not necessarily 'romantic'. The detailed components of urban structure - as seen perhaps in the Appendices of this thesis. But from a classical viewpoint, one might see that 'within the lines and shapes and symbols is a tremendous richness of underlying form'.
As we have seen, the significance of transport to the design of cities is not solely concerned with the travel function of routes, but the way in which those routes essentially link together in a structural fashion. Of the spatial and physical elements of the city, districts and 'centre' may be seen as composite or emergent entities: a city can be designed from the bottom up without them. Buildings and plots, though elemental, do not, like routes, forCp219YOWlSZlRBNCRWf9nw==m a single contiguous structure. Hence it is possible to interpret the route structure as the essential building block of the physical layout of the city.
There is more to a city than bricks and mortar - and, assuredly, asphalt and street patterns. However, a city does possess physicality: it is embodied by a physical structure that is constructed from simple elements that somehow interact and grow together to give rise to a complex whole. From the prerequisite of this material structure, urban vitality may emerge. Just as transport provision can contribute to design of urban structure, this urban structure can be seen as the key to urban creation.