Traffic Noise Prediction Model Research Articles

A critical review of some traffic noise prediction models

Traffic noise prediction models in the 1950s and 1960s were designed to predict a single vehicle sound pressure level L p at the roadside. These models were based on constant speed experiments, the predicted levels then being expressed as functions of speed, and with zero acceleration. Later models were not intended to predict single vehicle levels but to predict the equivalent continuous level L eq for traffic over a chosen period. Still later models predicted L eq under interrupted and varying flow conditions. Early models predicted linear levels whereas the later models predicted A-weighted levels. Several more recent models predict one-third octave band spectra. Early models assumed single point sources, some assumed short line sources, later ones double point, and even one with thirty-two point sources; some with different spectra. Six commonly used models and others under development are reviewed. The desiderata for traffic noise prediction models are discussed.

Road traffic noise prediction model in Thailand

A road traffic noise prediction model has been developed for environmental impact assessment in Thailand. The model was made under some assumptions; vehicles were classified into two groups and the average stationary noise level of each group was then determined from measurement of many vehicles. The power level of each group was determined by measuring the noise level of running vehicles. The average power level of running vehicles was subsequently described by a relationship between power level and the logarithm of the vehicle speed. Predicted noise levels were then compared with measured traffic noise levels from different roads involving 2, 4, 6, 8, and 10 lanes. The model is found accurate within ±3 dB(A) and it can be used for flat road traffic noise prediction in the cases of 2, 4 6 8 and 10 lane roads. The applicable speed of vehicles is between 30km/h and 140km/h and traffic noise levels can be predicted up to 80m from the roadside and at heights of 1 to 12m from the ground. ©

A model for insertion loss degradation for parallel highway noise barriers.

An algorithm is developed and validated for the prediction of the reduction, or degradation, of traffic noise barrier insertion loss when a second barrier is placed on the opposite side of the highway. The algorithm combines the basic emission, propagation, and barrier attenuation features of the Federal Highway Administration traffic noise prediction model with a geometrical acoustics approach for multiple reflections. The resultant model can accommodate any number of source lanes or receivers, three vehicle categories, and independently variable barrier heights and absorption coefficients. The model was validated against mathematical, scale model, and full scale field data received from other researchers, and has proved to be a good predictor of insertion loss degradation.

Highway traffic noise prediction with and without barriers—Some results and observations

Although the past decade has been a time of rapid increase in sophistication of models for predicting highway traffic noise levels including the effects of barriers, several important questions remain unanswered. This paper describes some barrier and near‐ground propagation modeling work recently completed and nearing completion at Penn State, and discusses questions arising therefrom. A point of view looking towards the needs of the utlimate users of traffic noise prediction models is attempted. Experiences in both indoor and outdoor barrier testing and with both controlled sources and free‐flowing traffic sources will be drawn upon in the presentation.

Are Earth Berms Acoustically Better Than Thin-Wall Barriers

The two most common highway noise barrier structures are earth berms and thin-walls. Yet the relative acoustical performance of these barriers is not well understood. Previous analytic, scale-model, and full-scale studies, comparing the acoustical effectiveness of thin-walls with that of berms and wedges, are reviewed. Additional data obtained by full-scale measurements, and in particular by a 1:16 scale-model study, are presented. The source-barrier-receiver geometry and model materials used were selected to simulate typical highway situations. Preliminary results indicate that, contrary to a recommendation in the Federal Highway Administration Highway Traffic Noise Prediction Model, thin-wall barriers and earth berms of the same height are about equally effective in reducing noise. In addition, the acoustical effectiveness of combining a wall with an earth berm was found to be quite similar to that of using thin-wall barriers alone. The practice of erecting relatively low walls on top of earth berms was found to be acoustically sound. (Author)

Sensitivity of predicted barrier attenuations to errors in specifying ground plane geometry

When the ground behind a noise barrier may be regarded as acoustically locally reacting, and where it has reasonably level topography, there is a plausible rationale for a traffic noise prediction model based on barrier diffraction of geometric image terms with coherent summation. Often in real life, however, even when sideline terrain surface is essentially plane, its plane is neither coplanar with the highway pavement nor even parallel to it. Defining the ground “plane” from measurements on the site, moreover, is not a task likely to be done with great precision in normal noise assessment practice. The sensitivity of traffic noise level predictions to errors in ground‐plane location then becomes of interest. In this connection a study has been made of a series of ground‐plane configurations approximating to cases arising in practice. Each case has been perturbed systematically, and the resulting differences in predicted noise levels have been observed. It has been particularly of interest to note the decrease in sensitivities resulting from averaging over frequency and over a traffic line. [Work supported by FHWA.]

The effect of stoplights on traffic noise

A study was undertaken to determine how the noise level due to free‐flowing traffic is affected by the insertion of a traffic light. Field measurements were taken at eight different traffic light locations, representing two configurations; that of two intersecting straight roads and tee junctions. A reference level, measured at a point where traffic noise was unaffected by the intersection, was used in conjunction with the NRC traffic noise prediction model to assess the change in noise level in the region about the traffic light.

Prediction versus reality: An evaluation of the NRC traffic noise model

In order to evaluate the NRC traffic noise prediction model a program of taffic noise measurements has been undertaken. An array of ten microphones, sampled simultaneously, is used to provide information on the propagation of traffic noise, in terms of Leq and other statistical descriptors, for a variety of traffic speeds, car‐truck mixes, and site configurations. At present, eight sites with free‐flowing traffic have been studied. Five of these were open sites with most of the traffic stream visible from the measuring positions, and three were located in residential streets perpendicular to a freeway. The attenuation with distance of Leq is presented as a function of the effective receiver height, and compared to that predicted by the NRC model.