This paper uses sets of experimental data, concerning commercial vehicles, to study the correlation between pass by and stationary noises through measurements executed according to external noise standards. We consider two sets of experimental data: before the new legislation (higher levels) and lower levels satisfying the new limits in Brazil. In addition we calculate the Loudness in sones, from the octave band noise spectrum, and compare the results with the usual evaluation in dB(A), with the purpose of emphasizing the qualification besides the quantification aspects and promoting conditions for people understanding. Besides the overall noise, we show the bandwidth contribution for each parameter and analyse the spectrum profile associated to the “A” weighting curve applications. The discussions, conclusions and recommendations are supported by regression curves and graphics taken from the measurements effectuated involving the chosen parameters.