关键词: 通勤时间, 人口密度, 建成环境, 调节效应, 多层次模型, 上海

Abstract:

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.

Key words: commuting time, population density, built environment, moderating effect, multilevel model, Shanghai