Background

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.

Material and methods

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.

Results

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.

Conclusion

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.

中文翻译：

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新的地铁系统和主动出行：自然实验

背景

我们使用发展中城市中的第一个地铁系统作为自然实验，研究了新地铁对模式转换和主动出行的影响的因果推断。

材料与方法

该治疗小组由来自步行800米之内的社区居民到新的地铁站组成。第一个对照组由居住在离最近车站步行距离处和外面的居民区组成，居民组距离最近的车站只有1.6公里，而第二个居民组则位于离自行车出行地点5公里的地方。这些组是由针对本地过境的规划实践和对主动出行的经验研究确定的。在新地铁发射前完成基线出行行为调查的5627名参与者中，有1770名在地铁运营后一年返回并完成了后续调查，其中包括治疗组的833名参与者和两种类型的937名参与者。对照组。

结果

我们的纵向数据分析显示出各种旅行行为变化。通常，过去坐公交车的人都乘坐地铁。上班时间每天平均使用地铁30.9（28.8–33.3）分钟，非上班时间每天使用16.6（14.9–18.7）分钟。步行时间最多减少19.7分钟（p <0.001），而骑行每天减少22.1分钟（p <0.001）。新地铁前后，汽车和电动自行车的使用率基本保持不变，治疗组和对照组之间没有差异。

结论

自然实验研究在发展中的城市环境中提供了关于新地铁对主动出行的影响的因果推断的第一批经验证据。一个新的地铁不一定会促进积极的出行增加或减少汽车使用，因此在对城市轨道交通投资的影响做出一般性假设时需要谨慎。我们建议当地的城市和交通规划知识可能有助于设计和解释交通与健康方面的复杂自然实验。