In urban traffic vehicle use leads to running conditions which vary essentially according to torque and speed. An experimental multiparametric analysis has been carried out on this subject. The results of the experiment confirm the main noise causing parameters. Noise prediction formulae can also be drawn up for any engine running conditions. As a result of this analysis the noise of one of the engines could be reduced by 7 dB (A) by acting on combustion and mechanical parts, as well as on sound radiation.