推文人 | 黄娜群（南京审计大学）

原文信息：Yizhen Gu, Junfu Zhang and Ben Zou. 2018. Subway and Road Congestion. Working Paper.

 

1 引言

 

交通拥堵是很多城市面临的问题。很多政府从需求和供给的角度进行管制。在供给方面，地铁被认为是有效的减轻拥堵的方式。 在中国，在2000年只有3个城市有400公里的地铁，但是在2017年，已经有30个城市有5000公里的地铁。但是另一方面，建造地铁的成本也非常高。这篇文章研究地铁是否有效降低拥堵。

 

2 数据

 

这篇文章在数据方面有两个较大的优势。1. 用了2016.08-2017.12期间25个城市45条新地铁的建设。 2. 来自百度地图的路面交通信息，实时的拥堵情况，2016.8.1-2018.1.31日特定道路的每小时速度的数据。

 

3 实证方法

 

 

4 实证结果

 

地铁对降低拥堵有影响，第一周大概降低2.5%，第五周降低6%，效果在第六周开始下降到低于5%，12个月后趋于稳定。此外，作者还建立了福利的模型，模型表明交通拥堵的降低带来的时间的节省低于政府建设地铁的补贴，即收益低于成本。

 

 

Abstract

 

We estimate the effect of subways on road congestion. Existing empirical studies have been constrained by small numbers of treated cases and imperfect measures of road speed. We study 45 subway line openings across 25 Chinese cities, and use big data from mobile devices that generate high frequency speed information at the road segment level. We adopt a difference-in-differences approach that compares changes in speed in nearby road segments after a subway line opens with contemporaneous changes in road speed in control cities. We find that subways increase rush-hour speed in nearby roads by about 5%. The magnitude of the effect exhibits a hump-shaped pattern: Speed increases in the first few weeks after subway line opening and then declines and stabilizes. The effect is concentrated in initially congested road segments and declines quickly over distance. Evidence on road speed is corroborated by substitution patterns between modes of transportation. We build a simple conceptual framework of transportation mode choices as a guidance for analyzing the welfare impacts of subways. Using data from Beijing, we find that benefits from saved driving time and reduced congestion externality is smaller than the welfare loss due to government subsidies in subways.