Research

Job Market Paper

This paper shows that road-closing policies may have adverse short-run effects on pollution by reallocating traffic toward more congested roads. I study the impact of the 2016 closure of the Voie Georges Pompidou, a one-way expressway crossing downtown Paris, on traffic and pollution displacement. To do so, I rely on a difference-in-difference strategy based on the directi on and the timing of traffic, which I implement on detailed road-sensor data. I show that the closure lowered average speed by over 15% on two sets of substitute roads: central streets nearby and the already congested southern ring road. Using air quality data, I show that NO2 emissions increased by 6% near the ring road and by 1.5% near local roads.  The reduced-form results on traffic are quantitatively consistent with a calibrated model 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 massive pollution increase because of the U-shaped relationship between emissions and traffic speed. Overall, I estimate that up to 90% of the pollution cost was borne by lower-income residents around the ring road, who lived far away from the new amenity created by the closure and mostly outside the jurisdiction responsible for the closure decision. Finally, I study counterfactual closure scenarios to assess under which conditions those adverse effects could have been mitigated.  

Work in Progress

The public debate about the removal of roads in a city shows extreme positions, each party suggesting that the choices are obvious. Some argue that climate issues justify a major reform of the organization of cities. Others observe that the corresponding roads are widely used and that their removal surely comes at high cost. However, the road paradoxes suggest that the problem is more complex. In this sense, one might wonder to what extent should the road supply be reduced. In this paper, we develop a theoretical model aiming at providing a framework for determining the cases in which the removal of express roads may be justified in the context of cities decarbonization. In addition to the possibilities of mode switch and the scarcity of public space, its specificity is based on the introduction of two groups of users: the "captives" of the car (or inelastic car-commuters) who do not have access to alternative solutions, and the "non-captives" (elastic car-commuters) who can switch to other modes of transport (public transport or new alternative modes). By introducing pollution externalities in the model, we show that in some cases, a marginal reduction in the road supply can increase the welfare cost. As such, the idea of a drastic adjustment is at the heart of the model.



Policy notes

Media coverage: La tribune (05/2021), Le Monde (05/2021), BFM (05/2021), Marianne (03/2022), Polytechnique Insights (05/2022)