Department of Urban Planning and Design, The University of Hong Kong, Hong Kong.
Department of Urban Planning and Design, The University of Hong Kong, Hong Kong.
Environ Int. 2020 May;138:105605. doi: 10.1016/j.envint.2020.105605. Epub 2020 Mar 7.
We used the first metro system in a developing city as a natural experiment to investigate the causal inference in the new metro's impact on modal shift and active travel.
The treatment group was formed by residents from neighbourhoods located within the 800-m walking distance to new metro stations. The first control group was formed by residents lived 1.6 km away from and outside of walking distance to the nearest station, and the second was 5 km away and outside of cycling distance. The groups were determined by local transit-oriented planning practice and empirical studies on active travel. Of the 5627 participants who had finished a baseline travel behaviour survey before new metro launched, 1770 returned and completed the follow-up survey a year after the metro's operation, which consists of 833 cohort participants in the treatment group and 937 in the two types of control groups. We used a difference-in-difference method to make before and after comparisons of travel behaviour changes between treatment and control groups.
Our longitudinal data analyses revealed diverse travel behaviour changes. In general, people who used to take bus have adopted metro. The average metro usage was 30.9 (28.8-33.3) minutes daily for work trips and 16.6 (14.9-18.7) minutes daily for non-work trips. Walking time decreased 19.7 minutes at most (p < 0.001), and cycling decreased 22.1 minutes daily (p < 0.001). Car and e-bike usages remained largely unchanged before and after new metro, without difference between treatment and control groups.
The natural experiment study provided the first empirical evidence in a developing city context on causal inference in new metro's impact on active travel. A new metro does not necessarily promote active travel increase or car use reduction, calling for caution in making general assumptions about the effects of urban rail transit investments. We suggest local urban and transport planning knowledge could be useful in designing and explaining the complex natural experiments in transport and health.
我们以一个发展中城市的首条地铁系统为自然实验，调查新地铁对出行方式转变和积极出行的影响的因果关系。
治疗组由位于新地铁站 800 米步行范围内的社区居民组成。第一对照组由距离最近地铁站 1.6 公里且不在步行范围内的居民组成，第二对照组由距离地铁站 5 公里且不在骑行范围内的居民组成。这些组是通过当地的以公共交通为导向的规划实践和关于积极出行的实证研究确定的。在新地铁开通前完成基线出行行为调查的 5627 名参与者中，有 1770 名返回并在地铁运营一年后完成了随访调查，其中治疗组有 833 名队列参与者，两种类型的对照组各有 937 名参与者。我们使用差值法对治疗组和对照组之间的出行行为变化进行了前后比较。
我们的纵向数据分析显示出多样化的出行行为变化。总的来说，乘坐公共汽车的人转而使用地铁。平均而言，人们每天用于工作出行的地铁出行时间为 30.9 分钟（28.8-33.3 分钟），每天用于非工作出行的地铁出行时间为 16.6 分钟（14.9-18.7 分钟）。步行时间最多减少 19.7 分钟（p<0.001），骑行时间每天减少 22.1 分钟（p<0.001）。汽车和电动自行车的使用量在新地铁开通前后基本保持不变，治疗组和对照组之间没有差异。
自然实验研究为发展中城市背景下新地铁对积极出行影响的因果关系提供了第一个经验证据。新地铁不一定会促进积极出行的增加或减少汽车使用，这在对城市轨道交通投资效果做出一般假设时需要谨慎。我们建议，当地的城市和交通规划知识在设计和解释交通和健康方面的复杂自然实验方面可能是有用的。
