Experimental determination of the geographical variations in vehicle fleet composition and consequences for assessing low-emission zones

Abstract

Low emission zones are frequently envisaged as a means of decreasing air pollution in city centres. In the present study, we used video monitoring to characterize the in-use local vehicle fleet at several points in the Île-de-France region (which includes the city of Paris), enabling accurate description of the type of engine and vehicle age and emission standard, which together determine their pollutant emission levels. Local vehicle fleets differed from French national estimates, as further confirmed by a Regional Mobility Survey. Both approaches (video monitoring and mobility survey) demonstrated geographical differences in the proportions of diesel and of recent vehicles. Economically advantaged areas, with lower rates of polluting and diesel-fuelled vehicles, are thus further advantaged as regards air quality and less affected by driving restrictions. Simulation of pollutant emissions demonstrated the sensitivity of the estimates to local fleet composition. They also raised the important contributions of traffic outside the city centre, of heavy vehicles and cold starts. Knowledge of the local vehicle fleet is thus important for designing low emission zones that will be effective in terms of air pollution and equitable in terms of geographical areas.