Interdire les voitures pour promouvoir les vélos ? Une étude sur la ville de Tours

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27 November 2023

We study the effect of the closing of the Wilson Bridge (in the French city of Tours) to cars between August 13, 2020 and May 24, 2021 on bicycle ridership. We use the daily data from bicycle counters available on the OpenData Tours Métropole Val de Loire website between June 2, 2016 and May 24, 2021. In order to take into account other factors that may impact cycling, we collected data on control variables related to the timing, the climate and the COVID pandemic. We argue that calculations based on average bicycle ridership comparisons tend to significantly overestimate the effect of closing the Wilson Bridge to cars (a 20% increase when comparing one specific month before and after the closing). Indeed, the increasing trend in bicycle use and growing environmental awareness are very strong confounding factors. Using an interrupted time series analysis, we find that this closure would be associated with a 7.23% (CI95%: +0.1%; +14.7%) increase in bicycle traffic. We performed several robustness tests and falsification tests that allowed us to confirm that there was indeed an increase in bicycle traffic. We believe it is important to conduct this type of study, especially when there are multiple exogenous shocks. Finally, we highlight some limitations of our methodology. In particular, because of the data used, it is impossible to clearly separate the effect attributable to a specific development from the totality of bicycle developments made during the COVID pandemic. One should stay particularly cautious with the results of the present study.
Nous avons étudié, pour la ville de Tours, l’effet de la fermeture du Pont Wilson aux voitures entre le 13 août 2020 et le 24 mai 2021 sur la fréquentation cycliste du pont. Nous disposons de données quotidiennes de compteurs vélos entre le 2 juin 2016 et le 24 mai 2021, de variables de contrôles calendaires, climatiques et sanitaires. En recourant à la méthode des séries temporelles segmentées, nous trouvons que cette fermeture est associée à une hausse de 7,23 % (IC95 % : +0,1 % ; +14,7 %) du trafic cycliste. En raison de certaines limites inhérentes à nos données (e.g., changements de compteurs vélos, aménagements cyclistes transitoires dans la ville de Tours), il semble toutefois difficile d’imputer la totalité de l’effet obtenu à la fermeture du Pont Wilson.