人口密度对居民通勤时耗的影响及条件效应——来自上海证据

基于上海市1 605个居民抽样样本,利用多层次线性回归模型,探讨了街道尺度人口密度对个体居民通勤时耗的影响及条件效应。在控制了个体社会经济属性、通勤方式和其他建成环境要素后发现,高人口密度总体上会增加居民通勤时耗,而且其作用是有条件的,主要受“设计”“地铁站可达性”“到就业中心距离”和“通勤方式”的调节。具体而言,提高街道路网密度和高速路密度,缩短居住地到就业中心距离,提高地铁站密度,鼓励居民采用地铁方式通勤,减少小汽车使用,都可以显著降低人口密度对通勤时耗的增加作用。因而,通过优化城市建成环境和调节人口密度来降低过长的通勤时耗是可行的。

Impacts and Conditional Effects of Population Density on Commuting Duration: Evidence from Shanghai

Given that long commuting duration is considered as a crucial problem of urban transportation, urban planners and geographers explored the impacts of built environment on commuting duration in order to reduce long commuting duration and alleviate traffic congestion. However, the findings on the connection between population density and individual commuting duration are inconsistent. Some literature showed that population density and individual commuting duration have a negative correlation, while others found a positive correlation or an insignificant relationship. Secondly, previous literature on individual commuting duration paid little attention to the conditional effects of population density. Just as Jane Jacobs remarked at The Death and Life of Great American Cities, “No concentration of residents, however high it may be, is ‘sufficient’ if diversity is suppressed or thwarted by other insufficiencies”, the impact of population density on commuting duration may depend on the other built environmental attributes. Furthermore, previous studies focused mainly on the cases in developed countries and far less on developing countries especially China whose urban built environment is characterized by larger population size and higher density. Based on a sample of 1 605 individuals from the “the Yangtze River Delta Social Transformation Survey (FYRST)” Project in Shanghai in 2013, this study examines the impacts and conditional effects of population density at the sub-district spatial level on individual commuting duration by using hierarchical models. Controlling individual socioeconomic attributes, commuting modes, and other built environmental attributes including diversity, design, accessibility to transit and distance to the job center, the random intercept model estimations show that individual commuting duration is positively associated with population density at the sub-district spatial level. One possible reason is the traffic congestion resulting from extremely high density and the job-housing imbalance. Moreover, this effect of population density on commuting duration is conditional on the “design”, the “accessibility to metro”, the “distance to the job center”, and the “commuting mode”. Specifically, higher road network density and highway density, shorter distance to the job center, higher metro stations density, and encouraging commuting by metro instead of driving could diminish the duration increasing effect of population density. But the expected conditional effect of “diversity” is not significant and not supported by this article. Thus, it is feasible to reduce commuting duration and traffic congestion by optimizing built environment and adjusting population density. Firstly, it’s necessary to point out that the advocated concept of compact development should orient at reasonable high density instead of over-concentration. Secondly, planners should pay more attention to encouraging job-housing balance, including both quantitative and structural balance. Last but not least, it is important to expand the underground space to encourage commuting by metro and to construct the highway to shunt the traffic flow for the sake of shortening commuting duration and improving traffic efficiency.