o decrease traffic pollutant emissions, numerous agglomerations envisage measures such as Low Emission Zones allowing only the less polluting vehicles to drive in dedicated areas. However, their implementation and efficiency depend strongly on the local vehicles fleet composition and on its possible variability as regards the areas. The analysis of the Île-de-France mobility survey and an in-situ observation campaign through video monitoring enabled a detailed characterization of vehicle fleet composition as regards motorizations and emission regulation. These two means of observations demonstrated significant differences with the National fleet composition estimation and important territorial variability, regarding Diesel share and vehicles renewal. 'Well-off' territories with less Diesel and more recent vehicles would thus be advantaged as regards air quality and less affected by traffic-restriction measure focused on old and polluting vehicles. Simulation of pollutant emissions demonstrates the sensitivity as regards fleet description. Furthermore the traffic out of the A86 highway (the second ring road around Paris, France), heavy vehicles and cold start represent significant amounts of emissions that would not be decreased by a restriction area. Local fleet specificities and variability are thus important for implementing a Low Emission Zone that would be efficient as regards air pollution and spatially equitable.