Freeway Traffic Noise Prediction And Evaluation Research Based On Equivalent Noise Source Position Located At The Shoulder Assumption

As the freeway operating mileages have increased year by year in China, theaccessibility has become higher and higher. The traffic noise that freeway generatedhas a great affect on sensitive points within the scope of traffic noise. To weaken oreliminate this impact, accurate analysis and evaluation to the intensity of trafficnoise needed to be done after the completion of freeway engineering feasibilitystudy. Although the traffic noise prediction models widely used in engineering haveacceptable prediction accuracy, but these models have the same unresolvedproblems that existed in FHWA model because engineers had only done this workthat the parameters and corrections terms of FHWA model were optimized andre-corrected according to the actual situation in China. Within these problems, theline sound source assumption does not match with the actual traffic flow, whichlocates at7.5m away from equivalent carriageway and1.2m high from the ground.Therefore, three studies that freeway traffic noise measurement experiment schemeswere designed, freeway traffic noise prediction model was established and freewaytraffic noise impact assessment were carried out by using systems engineeringprinciples and mathematical statistics methods. The studies could provide atheoretical basis for freeway traffic noise prediction and evaluation work.On the basis of analyzing different traffic noise models established in homeand abroad, the assumption that equivalent sound source was located at the shoulderwas provided. Furthermore, the coefficient that A vehicle acoustically equivalent toB vehicle and the discrete method of vehicle speed were used to construct thephysical model of equivalent sound source and then the intensity of the equivalentsound source calculation formula was deduced. According to the measured data,freeway traffic noise attenuation law was revealed and the attenuation model wasestablished under normal conditions in acoustic irradiation region. Finally, combinethe source strength model and attenuation model to established freeway traffic noiseprediction model.After summarizing the advantages and disadvantages of five traffic noiseevaluating indicators, the characteristics of traffic noise’s influence extent different with time and space changes was analyzed. Thus, the viewpoint that weightedequivalent noise level indicator should be used when evaluating traffic noiseinfluence was provided. What’s more, traffic impact grading criteria was establishedto make the impact assessment work more practical operational. Based on thegrading criteria, the concept of traffic noise service levels was provided todetermine whether noise reduction measures should be taken and what type measureshould be taken.Finally,"B" freeway traffic noise was select to be a study case to check thefeasibility of the prediction model proposed and evaluation method in previouspaper. The predictive values of the proposed model, the predictive values of themodel given by environment impact assessment specification and measured valueswere compared and analyzed in the case. The result indicates that the proposedmodel has a good predictive result.