Displacing Congestion: Evidence from Paris

This paper shows that road-closing policies may have adverse short-run effects on pol-lution by reallocating traffic toward more congested roads. I study the impact of the2016closure of the Voie Georges Pompidou, a one-way expressway crossing downtown Paris, ontraffic and pollution displacement. To do so, I rely on a difference-in-difference strategy basedon the direction and the timing of traffic, which I implement on detailed road-sensor data.I show that the closure lowered average speed by over15% on two sets of substitute roads:central streets nearby and the already congested southern ring road. Using air quality data,I show that NO2concentrations increased by6% near the ring road and by1.5% near lo-cal roads. The reduced-form results on traffic are quantitatively consistent with a calibratedmodel of shortest route choice, which allows me to recover the underlying rerouting patterns.Even though few displaced commuters diverted to the ring road, they triggered a massivepollution increase because of the U-shaped relationship between emissions and traffic speed.Overall, I estimate that up to90% of the pollution cost was borne by lower-income residentsaround the ring road, who lived far away from the new amenity created by the closure andmostly outside the jurisdiction responsible for the closure decision. Finally, I study counter-factual closure scenarios to assess under which conditions those adverse effects could havebeen mitigated.