Onboard System to Measure the Noise Radiated by Individual Vehicles to the Near and Far Fields

Road traffic noise amounts to roughly half of the overall ambient noise. Usual emission (vehicle emission limits) and immission (barriers, sound-reducing windows) noise control techniques have not been enough to decrease significantly the annoyance by road traffic over the last three decades. The positive effect of these control techniques has been counteracted by the increase of traffic density. Moreover, the traffic noise annoyance is highly correlated with the maximum noise levels usually produced by aggressive drivers. However, current traffic noise measurement systems are based upon an overall assessment, so that they are unable to discriminate between quiet and noisy drivers. Therefore, a near field noise measuring system is proposed in this research that is able to measure the contribution of each vehicle to the road traffic noise, allowing the detection of noisy drivers. The system is based on two onboard microphones, one for the engine noise and other for the rolling noise.

Experimental results are provided that demonstrate the performance of the proposed system on five drivers, along suburban and urban courses of a large city, with petrol and diesel vehicles. The analysis of concurrent acoustical and driving condition data reveals that the system is capable of discriminating clearly those vehicles generating the maximum noise levels

Therefore, we demonstrated that harsh drivers radiate to the near field noise levels 5-9 dB higher than the average of 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 harsh acceleration and deceleration. An excellent agreement is obtained between the noise levels measured at the far field and these extrapolated from the near field.