Investigating the effect of marginal trees cover and longitudinal slope of forest road on noise entrance of Truck engine in Kheyrood forest

Roads and other linear structures are the most important examples of human activities, and it can be mentioned that they have the most critical environmental effects on the natural habitats and ecosystems of the world. One of the most obvious of these adverse effects is environmental pollution, which has received more attention in the last three decades.The purpose of this study was to investigate the sound level of a heavy vehicle engine with a high engine volume in two different longitudinal slopes of a forest road and to identify the type of relationship between decreasing sound intensity and increasing distance from the road.

In order to measure the sound intensity, eight stations were used as acoustic measurement points along 20 km of the main one-way forest road of Teaching and Research Forest from Tehran University ,with low (2-5%) and high (8-11%) longitudinal slopes and Zero (roadside), 25 meters, 50 meters, 75 meters, 100 meters distances into the mass and downstream of the road and the axis of the road (closest situation to the car engine) were selected.The average sound level emitted from the Benztruck was 2624. This research was performed by the SL-4023SD digital audiometer with an accuracy of 1.5 dB and a resolution of 0.1 dB. The factors such as ,mean car sound level for a vehicle with constant engine volume, longitudinal slope in two levels, distance from the road in five levels were measured and analysis of variance was performed by GLM procedure whith using SPSS software.

In stations with longitudinal slope of the lower class by 58.7% and in stations with longitudinal slope of the upper class by 56.6%, a decrease in sound intensity was observed compared to the roadside. In all stations, the greatest decrease in sound intensity was recorded at distances of 0-25 meters from the roadside. In general, the type of relationship between decreasing sound intensity with increasing distance in longitudinal slope stations of the lower and upper class is logarithmic.

According to the results, it can be seen that the longitudinal slope of the road did not have much effect on the intensity of sound emitted from the road. In this study, all variables, both independently and dependently, significantly affected sound penetration. The results of this study showed that the sound intensity decreased by moving away from the sound source. Careful design of road technical specifications such as longitudinal slope, maintenance of road pavement, the presence of vegetations on the roadside and prevent its destruction, maintaining and restoring the density of trees in the roadside mass, combined planting of broadleaf and coniferous species can be Somewhat reduce the intensity of sound emitted from the road.