Low emission zones and traffic congestion: Evidence from Madrid Central
利用马德里高频率交通数据，研究发现低排放区政策减少了区域内交通流量，但导致交通向其他区域转移，且效果在7个月后消失，可能与车辆更新有关。
The aim of this paper is to shed light on the effect of Low Emission Zones (LEZs) on traffic. LEZs are areas in which access is restricted for the most polluting vehicles. They have been found to be effective in reducing pollution, while the expected effect on traffic is not clear. Using high-frequency granular data on traffic for the city of Madrid, I analyze whether LEZ schemes are effective in reducing flow and density within the area of implementation and whether they generate a displacement effect. Taking advantage of the exogeneity of the implementation timing, I develop a pre/post analysis based on time. Results suggest a reduction in traffic inside the restricted area and a displacement to all the other areas of the city. I find a switch to public transport for commutes directed towards the restricted area and rerouting of trips for destinations outside Madrid Central to be two of the possible mechanisms explaining these results. The reduction in traffic inside the restricted area gradually decreases over time and disappears after 7 months. This is consistent with the renewal of the vehicles’ fleet with unrestricted and cleaner vehicles generated by the policy.