Abstract

The economic growth happens mainly in city space while transport is the key factor for city. However, towns and cities across the world are bothered by transport problems, which chiefly caused by the competition from private cars;rising car use creates severe congestion and has led to a sharp decline in the patronage of public transport. Motorized vehicles also contribute to suburbanization and urban sprawl. Cities with high automobile dependency consume more land and energy, thus threatens the sustainable development of cities.

Motorization process in China has been accelerating and explosive since 2000, and many cities are experiencing congestions which has a trend of aggravating. Urban transportation and urban development are inevitable entwined. Automobile changes people's space conception, stimulates urban expansion and reshapes urban form and structure. Over years, research has sought to disentangle this problem by setting its own presumptions and data background, which almost subject to dispute, thus the research on Chinese motorization and its impact is a new challenge due to its special context.

This paper deals with the study from two respects: model analysis and empirical research. As a try to introduce urban economic models into this geography of urban transportation, the Mills model with a bimodal transportation system is used to analyze the relationship between city size, population density, car use and urban transport supply. This paper also focuses on the impact of motorization on city structure. The characteristics and trends of restructure of resident space, employment distribution and commercial space are discussed based on an international persperctive. The main conclusions include：

（1）The motorization process of China will keep on in a rather rapid speed and put more pressure on urban transport, lands consume and energy conserve.

（2）The Mills Model with a bimodal transport system（Bi-T Model）is introduced into this paper, and explains well the relationship between city wealth, rent of agriculture land, urban transport supply, prices of modes and car use, which makes them a powerful tool for policy analysis.

（3）There are strong links between China's motorization and suburbanization. The latter causes the former faster and leads to the phenomenon of passive motorization, and the former is an important force for urban restructure.

（4）The sensitive analysis reveals the relationship between several variables which is heuristic for policy making. For example, the urban expansion and decentralization are unavoidable in the framework Bi-T Model because the growth of income is a dominatnt factor to expand city's radius and make it less dense; the regulation on price of car use is an important policy option for boundary control because out-of-pocket cost can affect city size, population density and land rent greatly; and bus lane is an effective anti-motorization measurement.

（5）Making a reasonable price scheme, building a well-performed public transportation system and building a good infrastructure are important to guide people use less cars and develop a compact city.