A recent study by the Atelier parisien d’urbanisme indicates that reducing the speed limit to 50 km/h on Paris’ périphérique has led to a 20% decrease in traffic congestion and a 19% reduction in traffic-related accidents. While noise pollution has decreased notably, there are uncertainties regarding the impact on air quality, which shows reductions in nitrogen dioxide and fine particles. The link between speed reduction and air pollution remains inconclusive.