2.2 The Evolution of Transport and Urban Structure

From a historic state of‘balance', where transport spaces and buildings appeared to have an equal and complementary contribution towards forming the structure of settlements, transport systems subsequently came to dominate urban structure particularly as part of the Modernist paradigm.

Establish a perfect urban transportation system that matches urban land use development, coordinate the relationship between urban road transportation system and urban land use layout, the relationship with the city's external transportation system, and the relationship between various transportation modes in the city. This paper comprehensively analyzes the causes of urban traffic problems and puts forward the fundamental measures to comprehensively solve urban traffic problems. So that the urban transportation system can effectively support the economic, social development and urban construction, and obtain the best benefits.

2.2.1 The Relationship between Transport System and Urban Development

End along with the development of the city, the design of the traffic system with any changes in the development of the city experiences a process（city has developed from a small city to medium city, to the big city, to the megacities, usefully centralized layout to combination layout, the form and structure of the urban road traffic system will radically change subsequently.

Figure 2.3 Plan of Road

The city formed in the early stage is a small town, which is also the“old cit”part of the later developing city. Chinese cities because of the influence of the feudal rules and regulations, different grade“old city”of the city scale is different, but most of the present centralized layout for center, present the grid city state, despite of the primary and secondary points, but obviously width narrow, high density, more suitable for walking and non-motor vehicle traffic of the seats.

The development of a city to a medium-sized city may still be centralized, but there will inevitably be multiple sub-centers. A reasonable urban layout should gradually form a multi-center and relatively compact group layout by strengthening the construction of sub-centers, thus making the urban traffic distribution more reasonable. In the central group, the urban road network still maintains the basic pattern of the old city, while in the peripheral group, the modern three-level road network that is more suitable for motor traffic will be formed, and the grid pattern will still be maintained.

When a city develops into a large city, if it still follows the single-center centralized layout, it will inevitably suffer from excessive travel distance, traffic concentration, traffic congestion and urban efficiency. Therefore, the planning must guide the city to gradually form a relatively dispersed, multi-center group-type layout. The urban road system began to transform into a mixed road network.

The layout of megacities may be“combined city”, and the outer city of city will be further developed into several relatively compact peripheral cities based on the original peripheral towns.

2.2.2 External Transport

Urban external transportation refers to the general term of all kinds of transportation which is based on the city and is connected with the outside of the city. It mainly includes railways, highways, water transport and aviation. Railway, highway, water transport and aviation are national and regional transportation, and they all have industry plans adapted to national and regional economic and social development. On the one hand, the urban external transport planning should make full use of the national and regional transport facilities planning and construction conditions to strengthen the transport links between cities and towns in the city and develop the urban system in the city. In addition, according to the needs of urban economic and social development, we should further supplement and carry out local adjustment to improve the urban external transport planning.

Urban external transport is an important condition for urban formation and development. Modern city is also often an important hub of modern transportation, and the conditions of external transportation may restrict the development of the city. In order for a town to have a great development, its external transport capacity must be adapted to the production and consumption of the town, and the development of the city will also promote the further development of the city's external transport.

The layout of the city's external traffic lines and layout directly affects the development direction of the city, the layout of POE city, the direction of urban trunk road, the urban environment and the landscape of the city. Therefore, the city external traffic to the city's overall planning and bureau play a decisive role. The urban road traffic and external traffic have close connection, the urban external traffic lines and facilities should form the organic connection and transformation with the urban road traffic system.

The urban highways were introduced into urban areas, with their smooth flowing curves often set amidst landscaped contours of greenery, spilling in to occupy cleared or derelict urban land, almost seems to evoke the sense of a rural highway form penetrating the urban area, importing its accompanying territory in the process. This echoes the way in which the French boulevard, whose origin was also exurban, was introduced into cities in an earlier age.

In fact, we also find that the very notion of road‘hierarchy'was also supposed to have been derived from park layout.

In these quasi-rural prototypes, where intervening wayside activity is incidental, the emphasis is on strategic movement. In their application, especially in the cases of urban motorways and road hierarchy, the result is a downplaying of the existence, or importance in the‘hierarchy', of the access or frontage function- the urban, non-arterial functions of the street. It is hardly surprising, then, that these modern interventions are associated with creation.

2.2.3 The Influence of Modern Transportation System on Urban Design

At its most positive, the introduction of modern road systems opened up possibilities for new urban forms. Modern urban highways, with their sweeping alignments and tangle of intersections, can have a‘mad beauty of their own'. Their geometry may be considered as great works of art or functional sculpture. Driving along urban motorways, as they thread through the urban fabric and open up different vistas of the city, can represent an exhilarating urban experience unparalleled before the motor age. The motorway or freeway can become a‘place'or an‘ecology'in its own right.

Where modem road systems are introduced into existing urban areas, there is the potential for discord. Accordingly, a variety of ways of integrating the highway systems have been explored, whether treating the highway as a positive landscape in its own right or mitigating its physical impact with respect to the existing fabric.

However, it is not simply the immediate, concrete, physical intervention of transport infrastructure on the urban fabric that is a cause for concern. The imposition of a‘hierarchical'system of roads led to a radical restructuring of the whole system of public streets, and hence the structure of public space.

The advent of urban motorways went hand in hand with the notion of road hierarchy. This effectively‘elevated'the urban motorway type to a number one position, downgrading the previously pre-eminent role of traditional streets.

Railways are the city's main external transport facilities. Railway facilities within the city can be basically divided into two categories. One is passenger and freight facilities directly related to urban production and life, such as passenger station, comprehensive freight station and freight yard. The other is the special railway facilities not directly related to urban production and life, such as marshalling station, bus preparation and so on.

In such a way, local high streets and other traditional thoroughfares in the city were interfered with not only physically, but in a sense structurally, in a way that the earlier intervention of the railway had not. Certainly, the railways might have altered the local accessibility around stations, but they broadly reflected existing tendencies towards centrality and even helped to reinforce the centripetal nature of settlements.

By contrast, the advent of the new urban motorways and hierarchical principles could affect the city and its structure in more fundamental ways. In some senses they turned things inside out-creating new levels of accessibility at the periphery-or upside down, as formerly major streets were turned into backwaters or left'sealed off as precincts. Thus, the era of urban motorways heralded drastic surgery on many fronts, not merely on the physical side. Therefore, while‘hierarchy'might be an abstract principle, it nevertheless had very tangible consequences。

2.2.4 Highway Planning

Highway is domain, contact with other cities and towns within the area of road-town system planning should be combined with domain general layout and regional planning reasonably selected highway line and the direction of the station position. According to the trend of the development of the highway traffic in our country and existing problem, highway, especially the demand of the highway passenger and cargo diversion has been increasingly obvious, in order to meet the highway traffic development, guarantee the smooth traffic of highways and security, to adapt to the economic and technical requirements of highway construction, should as soon as possible for highway（first）freeway passenger and cargo diversion plan arrangement.

Highway classification: the classification of highways according to the nature and function of highways and their location in the national highway network is divided into national highway （national trunk highway）, provincial highway（provincial trunk highway）, county highway （county-level trunk highway, connecting various towns）and township road. Set up city can set up city road, serve as the highway that urban area connects city belongs to each county.

Highway classification: it is the classification of highways according to the task, function and traffic volume of the use of highways. Expressway is a closed special road for cars, is the national and provincial trunk road; First-and second-class highways are commonly used as major highways linking highways with cities above middle level. Three-level highways are often used as distribution roads connecting counties and towns. Four-level highways are often used as local highways to communicate with villages.

Large cities and large cities can set up expressway loops to connect various highways and connect with the urban expressway network. For the future development of small and medium cities, expressways should be separated from urban centers and connected with cities by special people（or general highway）.

The layout of roads in the city. The layout of highway in city area mainly depends on the national and provincial public planning, and the development of town system in city area should be satisfied.