Relationship between the noise radiated by a vehicle to the near and the far fields

Driving style can have a significant contribution to the noise radiated by individual vehicles. It has been reported that noisy drivers can radiate maximum noise levels which exceed the noise level of the mean traffic stream by 10 dB. Since regulations in most countries are based on averaged overall levels, it is rather difficult to discriminate and control the contribution of noisy drivers to the road traffic noise. In previous studies, an on-board measurement system was developed to evaluate engine and rolling noise levels in the vehicle near field. This system proved to be able to discriminate the noisiest vehicles in different environments and for different driving behaviors. We demonstrated that vehicles with aggressive drivers radiate to the near field noise levels 5-9 dB higher than the average of vehicles with normal drivers. However, most noise regulations are based on noise levels measured in the far field. Thus, we propose here a complete procedure for the extrapolation of the near field noise levels to the far field with a combination of analytical predictions and experimental measurements. Near and far field noise levels were concurrently measured on several trials including vehicle pass-by runs at constant velocities, and under aggressive acceleration and deceleration. An excellent agreement is obtained between the noise levels measured in the far field and these extrapolated from the near field.