This paper presents the application of a method estimating traffic noise levels in the centre of a big Greek city. The method requires a series of measurements to be carried out from 8.00 a.m. to 20.00 p.m. for every day of the week. The duration of each single measurement has to be determined due to various factors while simultaneous measurements or traffic flow are also needed. The results of the measurements are used to calculate the equivalent continuous A-weighted sound level L, ia (08.00-20.00). The noise level variations are attributed to the traffic flow changes and in addition a noise map of the examined area can be constructed. As an example, the case of Thessaloniki, a city with a population of about one million people, was studied. Three main roads of the city were examined during a whole month and measurements were conducted at a number of selected posi¬tions in each road for different traffic flow conditions.