拥挤效应、经济增长与最优城市规模

Congestion Effects,Economic Growth and Optimal City Size

本文运用新古典经济的框架建立了一个经济增长模型,系统分析了拥挤效应、经济增长与城市规模的关系。通过构造城市规模扩大而产生的拥挤效应函数,假设城市规模扩大产生集聚效应反应为拥挤效应的降低,并将拥挤效应进入生产函数影响经济的增长,分析经济稳态的演化路径,可得到最优的城市规模、合理的城市拥挤程度和稳定的经济增长速度,并分析了扰动稳态的变量对演化路径的影响。根据分析总结了三个结论:①长期,无论城市的拥挤效应是否影响生产函数,实物资本存量和经济增长速度均收敛于稳态,城市规模均收敛于最优城市规模,稳态时,城市聚集产生的正效应等于拥挤产生的负效应;②短期,外生冲击(基础设施的改善,绿化面积的增加,交通条件的改善等相关的引导政策)会影响长期经济均衡的位置,改变城市的最优规模,减少拥挤效应的措施会扩大城市最优规模;③横向而言,不存在统一的最优城市规模,不同等级的城市都有其不同的最优城市规模;纵向而言,城市的最优规模是一个动态的过程,随着时间变化,因不同的外部条件而改变。因此,在不同条件下,最优城市规模是存在且可变的,不存在统一的最优城市规模,城市化进程应该因时因地适度有序的进行。另外,本文还给出了一个估算最优城市规模的简单模型,可以从中推断最优城市规模扩大的速度关键取决于拥挤程度缓解或集聚效应增长的速度。

In the framework of neoclassical economics, this paper established an economic growth model, and made a systematic analysis of the relationship between congestion effects, economic growth and city size. Through constructing a congestion effects function caused by expansion of city size, we showed that expansion of city size can generate agglomeration effects, which are reflected as a decrease of congestion effects. Meanwhile, congestion effects can affect economic growth by entering the production function. In addition, by analysis of the evolution path of steady-state economic, we obtained the optimal city size, a reasonable congestion degree and the stable economic growth rate, and then explored the evolution path effect imposed by the factors which may disturb steady state. According to the analysis, we can draw three conclusions： （1） In the long term, no matter how congestion effects influence the production function, the physical capital and economic growth will converge to steady-state and the urban scale will converge to the optimal city size, and the positive effects produced by agglomeration are equal to the negative effects produced by congestion. （2） In the short term, exogenous shocks （improving infrastructure and traffic condition and increasing green-area and other related guidance policy） will affect the long-term economic balance, so measures of reducing congestion effects will expand the optimal city size. （3） Laterally, the optimal city size is no unified, and different levels of cities have their different optimal scales, Vertically, the optimal city size is a dynamic process due to different external conditions over time. Therefore, the optimal city size is variable under different conditions, and the process of urbanization should be moderate and orderly. In addition, this paper can extrapolate that the expansion of optimal city size depends on congestion mitigation or agglomeration growth by setting a simple model.