The role of mutual screening by vehicle bodies in traffic noise propagation throughout a built-up area

The paper presents the results of investigation of the sound field on a building façade neighbouring a busy road. The field simulation is based on programs which allow control of accuracy in description of a propagation process, as well as accuracy in modelling of a road and its surroundings. Considered interactions are straight-line spreading, reflections, and diffractions. The urban system modelling involves geometry of surrounding buildings and acoustical properties of their walls, road geometry and a traffic structure in lanes. By comparison of the simulation with the field measurements it could be confirmed that a proper accuracy has been obtained. Based on the verified simulation of the sound field, the efficiency of noise abatement means can be predicted depending on urban system parameters. In the previous investigation, moving vehicles were modelled as omnidirectional point sources (E. Walerian, R. Janczur, M. Czechowicz, J. Smirnowa, Possible improvement of acoustical climate. PART I: Measurements and theoretical description, Archives of Acoustics 35 (3) (2010) 307–332; R. Janczur, E. Walerian, M. Meissner, M. Czechowicz, Application of simulation program to specific urban situation, Applied Acoustics 70 (2009) 973–985). In this way, the required agreement between the simulation and measurement had been obtained for the upper part of façades. In the presented paper the free emission in the road space is replaced by emission disturbed by other vehicles’ presence. To consider their influence, the effect of mutual screening by vehicle bodies is included. The disturbed noise emission, when neighbouring vehicles are treated as semitransparent screens, offers a fully satisfactory agreement with field measurements for the case of a smooth façade. A noticeable improvement has been obtained for a shaped façade with a few meters depression in it. In the last case, the satisfactory agreement with field measurements has been reached when the proper reflection coefficient of the walls has also been assumed.