A modified noise-prediction model for highways with significant motorcycle traffic

Abstract

One of the undesirable outcomes of the rapid travel of a large number of vehicles on highways is the high level of noise pollution. Tehran is the most noise-polluted city in Iran, where the contribution of motorcycles to noise pollution is significant. In this paper, the equivalent sound pressure levels (LAeq,1h) were measured alongside seven highways in Tehran and were compared with the environmental guidelines. The traffic-noise-prediction model for highways proposed by the government (IR-TNM) was also evaluated based on the collected data from field measurements. The findings reveal that traffic noise levels at measured points exceeded the maximum noise level allowed by Iran's Department of the Environment. Also, there was a significant difference between the results of the prediction model and measured values at the measured points. As highway access for motorcycles in Tehran is not prohibited and their impact on highway noise is not considered in the IR-TNM prediction model, a modification of the model, considering the motorcycle traffic and re-estimating the coefficients, was performed using the Gauss–Newton method, which led to a better fit to the observed data both for the calibration and validation data sets.