A critical review of principal traffic noise models: Strategies and implications
Introduction
Noise prediction is one of the vital tools for town planners for noise abatement and control. This technique got a special impetus after the European Directive about Environmental Noise 2002/49/EC, wherein noise maps have been recommended for transportation sources and urban agglomerations (EU Directive 2002/49/EC, 2002). Consequently, many scientific models have been developed in recent years focussing on this aspect and introducing exclusively source emission and sound propagation empirical formulations. These models have been developed and validated in respective countries and brought in regular usage and are integrated with GIS interface for generating noise maps. Apart from the source characterization, advanced numerical methods including wave equation and continuity equation are employed to solve the sound propagation effects. These models thus utilize high speed processing computers and skilled operators for achieving the end objectives. Thus, it is imperative to analyze scientifically and compare these models so as to ascertain their suitability in general and also to find out the best approach amongst them for traffic noise modelling. Steele (2001) did an exhaustive critical review of various traffic noise models. However, some of these models have been revised in recent years, and thus it is imperative to update this comparison done by Steele (2001) based on technical attributes. The present work describes the strategies and implications of these models developed in recent years. The various models discussed in the paper are FHWA of USA, ASJ RTN 2008 of Japan, CoRTN of UK, RLS 90 of Germany, Son Road of Switzerland, Harmonoise of Europe, Nord 2000 of Scandinavian countries and NMPB-Routes-2008 of France.
Section snippets
FHWA model
The Federal Highway Administration Traffic Noise model (Barry and Reagan, 1978; FHWA TNM) computes a predicted noise level through a series of adjustments to a reference sound level. The reference level is the vehicle noise emission level, which refers to the maximum sound level emitted by a vehicle pass-by at a reference distance of 15 m.
where Atraffic (i) is adjustment for traffic flow, Ad represents the adjustment for distance between the roadway and receiver and
Comparison of models
It can be observed that the new principal models formulated and adopted in developed nations cater to all the aspects of road traffic noise modelling, from source characterization in terms of sound power level to sound propagation through different meteorological conditions and addressing the reflections, diffraction and absorption phenomena. The simpler engineering models like ISO 9613-2, RLS-90 produce an empirically based level increase with reflecting ground or attenuation with absorbing
Implications of traffic noise models
The exhaustive review of the principal traffic noise models thus evidently shows that empirical models used earlier have been replaced by new models based on scientific principles appending numerical methods as a consequence of increasing computer skills. Attempts have been made to separate the source and propagation part in order to allow independent updating of source and propagation models. It is very difficult to weigh the pros and cons of all different approaches specifically when all
Conclusions
The paper discusses a comparison of the principal traffic noise models developed and adopted in various countries. It is quite obvious that the source model may be different for all these models, however, there should be a harmonized approach for sound propagation modelling especially. The use of numerical methods for solution of wave equations for characterizing the meteorological factors although enhances the prediction accuracy, yet inculcates a lot of computation complexities and requires
Acknowledgements
The authors thank Mr. Anil Kumar, Chief Scientist, NPL and retired colleagues, Dr. V. Mohanan and Mr. Omkar Sharma for their help in this work. The authors thank CSIR-NPL in providing special grant for procurement of 24 hours noise monitoring system and other infrastructural support for the study. The financial support received from research projects NWP-45 and MIST is greatly acknowledged and appreciated. The authors shall appreciate any corrections, suggestions or updates of information.
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Author details: Naveen Garg is Senior scientist in CSIR-National Physical Laboratory working in the field of Acoustics and Vibrations. He is a Mechanical engineer specializing in Machine design,Vibrations & Acoustics, Measurement science and working in development and up-gradation of primary standards of sound pressure and vibration amplitude and R&D in Applied Acoustics. He has been involved in many consultancy and sponsored projects pertaining to EIA studies w.r.t. noise and vibration for govt. bodies like CPCB, ASI, DMRC, BMRCL, India. He has published many papers in national and international journals in the field of acoustics and vibrations and has been actively involved in the Key Comparison exercises in Acoustics and Vibration metrology with other National Metrology Institutes (NMIs) of the world that has led to publishing of Calibration & Measurement Capabilities (CMCs) of CSIR-NPL, India in BIPM, Paris Key Comparison Database (KCDB).