On September 22nd 1998, 35 French towns took part in a pilot experiment consisting in drastically reducing the vehicle traffic in the town centres. According to that scheme, INERIS, in association with the local Air Quality Monitoring Network AIRLOR, carried out a BTX sampling campaign over 3 days, in order to quantify the impact of the traffic restrictions on air quality. This campaign was carried out in the centre of Nancy, where traffic restrictions were imposed on an extensive area. Sampling sites were chosen close to the busiest traffic routes. Sampling was carried out using passive samplers, on 10 hours on each day of the campaign. Measurements show clearly that, over the 3 days, the traffic flow reduction led to a decrease in BTX roadside concentrations by between 30 to 80 %. These measurements correlate well with CO levels monitored at one of the sampling sites, and with the volume of traffic in circulation each day. The correlation between BTX and CO clearly indicates traffic as the main source of atmospheric pollution. Measured benzene levels over the 3 days are compared with statutory limit values in France and in Europe.