Chapter 2 Transport and Urban Structure

Generally, the site layout of the old city is relatively compact, and the road network is relatively close and narrow. High density makes traffic more dispersed. Narrow capacity, then can organize one-way traffic, suitable for dispersive traffic mode. In big cities, urban peripheral more put land layout, in order to adapt to the characteristics of long travel distance, requires traffic speed, to organize efficient sets the amount of traffic flow, match with high efficient road traffic facilities, it needs to have a distinct shunt type road network structure, compared to the old city, density is lower, width is wider ability to adapt to modern traffic will be larger.

The above analysis shows a general rule: different scale and different types of urban land layout have different traffic distribution and traffic requirements, there will be different road network types and modes, and there will be different road network density requirements and traffic organization methods. Therefore, different cities may have different road network types; different urban areas or sections of the same city may have different road network types due to different land layouts. Different types of urban trunk road network are closely related and closely coordinated with different urban land use patterns.

The functional division of urban road is from the beginning of the emergence of road.

Initial port of urban road is the main street and main street, the main road is main transport passage, and arrangement of main urban public buildings, commercial services is traffic sex and sexual life with the combination of roads, but in an age of traffic conflict are not outstanding, to distinguish the dredge and service is ok, is a kind of reasonable division of functions. The central axis of the early city was the main road, such as the cross street at the county level in ancient Chinese cities（Figure 5-8）and the well pattern road at the state level. With the development of the city, the extension of these roads became the development axis of the city.

The development of modern cities has brought the development of modern urban motorization, the urban road traffic and the separation of sexual life become necessary for the benign development of the city, the development of the city axis can still along the traditional mixed main road of development, and the lateral position arrangement in the center of the city road traffic and dredge, can guide the city more scientific and reasonable development. Transport and urban structure are closely, if not inseparably, associated and connected.

Traditionally, the layout of routes was formed in close association with buildings and public spaces, though in more recent times they tend to have been conceived apart, by different professions, following separate agendas. This thesis is an attempt to study how the transport network constitutes urban structure, and urban structuring contributes to urban design. Though the thesis focuses on the transport structure - the skeletal part of the urban whole -it is anticipated that through attention to the design of this structure, the creation of the whole may be better realized.

We discuss the differences of the traffic system in urban construction, especially the significance of urban structure and the contribution of urban role. To some extent, the degree of traffic structure design is equal to the structure of urban design.

Historically, different types of settlement forms are usually the result of the interaction between different traffic modes, and urban development and urban planning methods are also generated and developed to adapt to the new traffic system.

We consciously regard transportation design as a positive construction method, which lays a foundation for the mutual influence between traffic and different traffic.

2.1 Interpretations of Urban Structure

Urban structure refers to the forms and ways in which the various components of a city interact with each other, mainly including economic structure, social structure and spatial structure. In the process of urban development, it is not only the increase of buildings and the aggregation of residents, but also the formation of functional areas within the city, such as commercial, residential and industrial areas. At the same time, there are organic connections between functional areas, which constitute the whole city. The formation of various regions within the city and its distribution and configuration are called“spatial structure”or“internal structure”, short for“structure”.

2.1.1 The Importance of Transport-Constituted Urban Structure

The transportation system of a city, a region and a country is composed of various relatively independent and complementary traffic types. Urban traffic is a unique traffic system which is also composed of many types of traffic. Therefore, for urban planning and construction, there is often a concept of“urban comprehensive transportation”, which covers various forms of transportation existing in and related to cities.

From the perspective of regional relationship, urban comprehensive traffic can be divided into two major parts: urban external traffic and urban traffic. The relationship between the traffic outside the city and the urban traffic is interrelated and interchanging.

From the form, urban comprehensive traffic can be divided into ground traffic, underground traffic, road traffic, rail traffic, water traffic and so on.

From the nature of transport, urban comprehensive traffic can be divided into passenger traffic and freight traffic two major types. Passenger transportation is the human transport behavior, is the main body of urban traffic, distributed in every place of the city. Freight traffic is the movement of goods, the main part of the distribution in the city peripheral industrial areas and warehousing areas.

From the position of traffic, urban comprehensive traffic can be divided into traffic on the road and traffic outside the road.

City combined traffic can be classified according to the nature and mode of traffic. The planning of external transportation of various cities depends on relevant industry planning and urban system planning. All kinds of urban traffic are closely related to urban transportation system, road system and urban traffic management system.

（1）Urban external transportation. Urban external transport generally refers to the traffic between cities and other cities, as well as the traffic between urban areas and surrounding towns and villages within the scope of urban areas. Its main form of traffic is: aviation, railroad, highway, water carries. The city is often equipped with corresponding facilities, such as airport, railway line and station yard, long-distance bus station yard, port terminal and the route of attracting the city. The overall layout of external transportation in the city should mainly respect the planning of various professional departments and meet the requirements of urban system development and interconnection. In the central city planning, the connection between external transportation and urban transportation and the layout of external transportation facilities in the city should be paid attention to.

（2）Urban transportation. In the broad sense, “urban traffic”refers to the traffic within the scope of the city（district）, or the flow of people and things between various urban lands. These flows take certain urban land as the starting point, certain urban land as the end point, and through certain urban land.

Generally, “urban traffic”refers to the traffic on urban roads, which is mainly divided into freight transport and passenger transport. The traffic on urban roads is the main body of urban traffic, and urban passenger transport is the focus of urban traffic research. The development of modern big cities shows that rail transit（metro, light rail, etc.）in big cities and megalopolis will play an important role. In addition, water transport（ferry, ship）and other forms of transport will be available in some cities.

（3）Urban public transport. “Urban public transport”is a kind of transport that is closely related to urban residents in urban transport, and is the urban passenger transport using public transport tools. Including buses, trams, trolleybuses, subway light rails, ferries, urban shipping, taxis, etc.

（4）Urban transportation system. We usually take urban road traffic as a system to study. The urban traffic system is an important subsystem of the urban large system, which reflects the dynamic functional relationship of urban production and life.

The urban traffic system is composed of the urban transportation system（the operation of traffic behavior）, the urban road system（the passage of traffic behavior）and the urban traffic management system（the control of traffic behavior）. The urban road system serves for the completion of traffic behaviors of the urban transport system, while the urban traffic management system ensures the normal and efficient operation of the entire urban traffic system.

Urban transportation system is the basic component of the social, economic and material structure of a city. The urban transportation system connects the urban production and living activities scattered throughout the city, and plays a very important role in organizing production, arranging living, improving the effective operation of urban passenger and goods flow and promoting urban economic development. The urban land layout structure, size and even the urban lifestyle all need the support of a city's transportation system. Los Angeles' decentralized layout is inseparable from its dense expressway network; London's way of life depends on the subway network it formed in the 19th century. Manhattan's prosperity depends on the subway and bus system. The historical and cultural environment of Paris has not been greatly impacted by modern motorized transportation, which is inseparable from the developed subway network and bus network. The concentric development pattern of Chinese cities is related to the widespread use of bicycles and ground buses as passenger vehicles.

（5）Urban road traffic system. Urban road is the main channel, the urban traffic in the city and some outside the road passenger transport channel system, such as subway, overhead or ground independent setting of the special channel such as light rail, need through the site facilities and city road system, so we called the urban road system and urban transport system in the urban road traffic system.

Of the various candidates for being the‘building blocks'of the physical city - buildings, spaces, routes or boundaries - it is surely not the discrete buildings, but the contiguous spaces, routes or boundaries which constitute the primary structure of the city. An otherwise disjointed agglomeration of buildings, without reference to their connections in space, cannot comfortably be said to form a structure.

Buildings are commonly discrete objects, but even when conjoined to form terraces or other agglomerations, sooner or later they tend to be separated from other buildings by public thoroughfares. Similarly, plans showing plot boundaries reveal that agglomerations of plots tend to form insular blocks separated by blank spaces which represent access routes.

Figure2.1 Example of morphological plan.

Certainly, buildings and plots could easily be thought of as being part of urban structure, but it is argued here that the essential structure is that of the routes, in relation to which buildings are appendages, and plots interstices. Indeed, the circulation space within buildings, whether public or private, might be considered as extensions to the movement structure. However, in this case it is still the surfaces of accessible space that form the structure, not the solid walls or columns.

The significant feature of the transport network, then, is its inherent contiguity. From the scale of the individual building to the whole city, publicly accessible spaces are generally linked into a single network. This is a basic geometrical property which sets apart the access network from, say, buildings or parks. This makes transport a fundamental organizing feature, and gives it an importance that transcends the direct travel or traffic function of routes.

To say that transport is key to urban structuring does not imply that‘transport'as an urban function is more important than‘housing'or‘open space'. Nor does it mean that the buildings and land parcels do not affect the form of the resulting street pattern; clearly, street pattern will be influenced by a variety of non-transport factors, including topography, and social, economic and political forces. However, it does mean that close attention to the structural logic of the access network - including the transport policy sphere with which this is inevitably associated - is important for understanding how existing cities are structured and how new ones may be designed.

2.1.2 Facets of Transport-Constituted Urban Structure

To the extent that transport network structure includes the pedestrian network, it would encompass all routes and spaces occupied by pedestrians, which could include piazzas, podia, underground passageways and even building interiors（eg, shopping malls）. Therefore, in many circumstances transport network structure will equate with the structure of public space and urban structure in general.

Movement structure implies an abstract pattern of actual or potential movement. It might be represented by a diagram of recorded flows.

Insofar as the movement structure equates with actual routes, it is effectively coincident with transport network structure in its widest sense- and hence urban structure.

Figure2.2 Movement structure of central Glasgow.

Street pattern is a commonplace term which equates more or less with urban structure.

The word‘street'immediately implies an urban setting; the word‘pattern'implies the visual impression made by a layout regarded as a whole, as if observed from above. Pattern may also imply some sort of discernible order. Put together, the term‘street pattern'definitely implies an assembly of urban routes, which may be equated with the transport network or urban structure.

The terms transport network structure, movement structure and Street pattern are not synonymous with each other, nor are they congruent with some of the wider interpretations of urban structure（e.g., the appending buildings and plot boundaries）.

However, they do all share a common element, a core conception which is interpreted in this thesis as the essence of urban structure.

Two further terms may also be distinguished, which are taken to be more or less synonymous with urban structure - albeit at different scales. Settlement structure is taken to imply the overall urban structure for a settlement as a whole, while circulation structure implies the movement structure within buildings（or at the scale of buildings）. These terms may sometimes be used loosely in place of urban structure.

Overall, within the context of this thesis, there is not much of urban structure that does not imply the structure of access and movement by one form of transport or another. For many practical purposes, we may say that urban structure is transport structure, at least insofar as the structure of transport structure is the same‘structure'as that of urban structure.