Institute of Fundamental Technological Research

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.

Screening by vehicle bodies, Vehicle modelling

The adequacy of a model for the sound level close to a road is investigated by comparing resulting predictions for the sound level over a building façade with measurements. The road model involves the road geometry (the number and positions of traffic lanes), the traffic structure (vehicle flow rates and their average speeds in each lane) and equivalent omnidirectional point sources representing the vehicles. It is found that the assumed road traffic noise source model is adequate only for predicting levels over the higher part of the façade. However the investigation has allowed definition of what improvements are needed in the road source modelling to enable adequate predictions over the whole of the building façade.

Acoustical climate prediction, Noise sources modelling

In the paper, the simulation program predicting the sound level has been applied to one of buildings neighbouring a road. In the simulation are considered: geometry of road surroundings, the shape of the investigated building façade including, road geometry (number of lanes and their positions) and traffic structure (vehicle flow rates and their average speeds). Adjustable accuracy in an urban system modelling allows finding the model which is adequate to the real system. For the model of the accuracy limited by the simulation error due to vehicle speed estimation, by comparison with the field measurement, the model validation range has been established. Based on the simulation adjustable accuracy, possibilities of the validation range extension have been analysed.

simulation, traffic noise, noise protecting means

In the paper, predictions of relative sound level distribution on building facades in city-centres obtained by using the simulation PROP11 program are compared with measurements. The simulation involves the geometry of surrounding buildings, road geometry (number of lanes and their positions) and traffic structure (vehicle flow rates and their average speeds). The agreement between measurement and simulation results is tested for different directivity characteristics of an equivalent point source representing the vehicles.

predicted sound level in built-up area, vehicle noise emission directivity

In the paper, the PROP10 program is used to present the time-average sound level on façades of buildings in the vicinity of a crossroads. The propagation model within an urban system forming canyon streets includes the wave interaction with obstacles, multi-reflections from building walls and single and double diffraction at their wedges. For the current purpose the program is provided with a road model in which the vehicle route is divided into sub-segments with lengths and linear densities of emitted energy that depend on the traffic organization in the vicinity of the crossroads. The lengths of the sub-segments, where vehicles wait and are forced to a subsequent start and stop, depend on the flow rates on lanes, the equivalent vehicle length, the red and green light times and the speed of leaving a crossroads. The linear energy density at these sub-segments depends on a parameter characterizing the energy emitted during the starting of a vehicle. The time-average sound level is analyzed as a function of the enumerated parameters.

traffic noise, interrupted movement, canyon street