Noise pollution of the road network of the city by road transport

. The article is devoted to the analysis of noise pollution of a residential area by road traffic. It is noted that car noise is a great danger to human health, especially in large cities and industrial centers. Field studies of the noise characteristics of traffic flows in busy, dangerous sections of the road network of a large city have been carried out. It is shown that the level of car noise exceeds the maximum permissible sound level for any measured value of the flow intensity and distance from the road up to 35 m. The dependence of noise on the parameters of traffic flows is studied, analytical dependences are obtained, and correlation and regression analyzes are carried out. Measures have been proposed to reduce the level of automobile noise in busy sections of the road network of a large city.


Introduction
Road transport is one of the most significant sources of negative impact on the environment, which is especially pronounced in large cities and industrial centers [1][2].
In addition to chemical pollution of the environment with toxic substances emitted into the atmosphere together with exhaust gases, road transport also has a harmful vibroacoustic effect, with noise being a particular danger [3]. According to experts from the World Health Organization, traffic noise is one of the most important harmful factors affecting health, and is second only to air quality in terms of the degree of this influence [4]. In a number of works, the sanitary and hygienic aspects of the noise impact from vehicles on the health and quality of life of residents of urbanized areas are considered [5][6][7][8][9]. It has been shown that constant noise causes the same physical reaction in a person as stress and can affect the psychological state and stability of a person, lead to somatic disorders. Long-term exposure to noise levels above 75 decibels (dB) has a marked negative effect on the physical and emotional state of people, increases the risk of hypertension and coronary heart disease, leads to impaired hearing and cognitive functions. These consequences of the negative noise impact on the human body are found mainly among residents of cities where there is a high population density and a developed network of roads [10].
Studies by Weyde et al. have shown that children's health is most adversely affected by noise [11].
The level of car noise is determined by a number of factors, among which the most significant are the composition of the traffic flow, primarily the number of trucks and large buses in it, the intensity and average speed of movement. The noise characteristic of the traffic flow also depends on the quality and type of road surface, building features, the presence, number and type of green spaces, terrain, climatic and weather conditions [12][13].
It is expected that the scale and intensity of acoustic pollution of the environment by road transport will increase in the future, which is associated with urbanization and an increase in the level of motorization on a global and national scale [14]. In this regard, the study of the patterns of changes in car noise in urban areas, the establishment of strict quantitative dependences of the noise level on the parameters of traffic flows and other factors, as well as the development of methods to reduce the level of car noise on their basis, is an important and urgent technical and environmental task.

Materials and methods
In order to assess the dependence of the level of automobile noise on various parameters, field studies were carried out on sections of the road network of the city of Naberezhnye Chelny and the values of the equivalent sound level were measured at the highest hourly traffic intensity.
Field measurements were carried out on complex, problematic sections of the urban road network, characterized by a large number of traffic accidents compared to other sections, which was determined from the statistics of the traffic safety inspection and the accident map.
The noise characteristic of traffic flows was determined using a sound level meter of the first accuracy class in accordance with the requirements of the Russian standard GOST 20444-19; the measured value was the equivalent sound level Leq (dB). The measurements were carried out at a positive air temperature, at a wind speed of not more than 2 m/s. Simultaneously with the measurement of the equivalent sound level, field studies of the intensity and composition of traffic flows on the analyzed sections of the road network were carried out using the video recording method. The obtained results of experimental studies were analyzed using the programs Statistica and Microsoft Office Excel.

Results and Discussion
Studies of the noise characteristics of traffic flows were carried out at three intersections of the city of Naberezhnye Chelny, which are characterized by heavy traffic and a high level of accidents.
An analysis of the structure of traffic flows in the analyzed sections of the road network showed a significant predominance of cars in them, the average share of which is 93.9%. The share of trucks in the traffic is 1.2%, buses of various carrying capacities account for 4.8% of traffic and 0.1% for other vehicles. Measurements of the equivalent sound level from traffic flows were carried out during peak hours at maximum hourly traffic volumes. It is shown that the analyzed areas are subject to high acoustic pollution, the values of the equivalent sound level significantly exceed the maximum allowable level of 55 dB.
A check was made whether the obtained experimental data obey the normal distribution law, for which a graphical method was used. Figure 1 shows the results of the dispersion analysis of a sample of experimental data on measuring the equivalent sound level from vehicles, obtained in the Statistica program. Analysis of graph 1 allows us to conclude that the measurement results correspond to the normal distribution law. Therefore, for their processing, it is correct to use the methods of parametric statistics, both for testing hypotheses and for an adequate description of the results.
A correlation analysis of the data obtained from measuring the noise characteristics of traffic flows was carried out, according to the results of which it was concluded that the equivalent sound level depends mainly on the total number of cars with the observed flow parameters, namely, high traffic intensity and a significant predominance of passenger cars in it. cars. At the same time, the influence of other groups of vehicles on the magnitude of the noise characteristics of traffic flows is not so significant. The results of the correlation analysis of the dependence of the equivalent sound level on the composition of traffic flows are presented in Table 1. Since the highest correlation coefficient, equal to 0.975, was recorded for the variables: the equivalent sound level L eq and the total number of cars, the relationship between these two parameters was investigated. The graphical dependence of the equivalent sound level on the total number of cars has a logarithmic form, it is shown in Figure 2.
With a total traffic intensity varying in the analyzed sections of the road network within 2000-6000 vehicles per hour, the equivalent sound level varies from 73 to 82 dB, which is 1.3-1.5 times higher than the maximum permissible level equal to for a residential area 55 dB. To determine the mathematical dependence of the equivalent sound level on the total traffic intensity, a regression analysis was carried out, as a result of which the following formula was obtained: L eq =8 .1302⋅ln( N )+11 . 332 (1) Where: L eq -measured equivalent sound level, dBA; N is the intensity of traffic flows, avt./h. The value of the coefficient of determination R 2 =0.945 indicates a high dependence of the equivalent sound level on the intensity of traffic flows.
The analytical dependence between the noise characteristic of traffic flows and the traffic intensity of passenger cars also has a logarithmic form: L eq =3. 5043⋅ln( N l )+50.333 (2) Where: L eq -measured equivalent sound level, dBA; N l -the number of cars, cars / h. The determination coefficient equal to R2=0.904 characterizes the high dependence of the equivalent sound level on the number of cars crossing the studied section of the road network per unit of time.
Studies of acoustic pollution of the residential area were carried out on sections of the road network located in densely populated areas of the city, where there are pedestrian and bicycle paths, walking areas, shopping and entertainment centers, cafes and other centers of attraction for citizens, some of them on a small (20-30 m) distance from the road. In this regard, it was expedient to study the dependence of the noise characteristic on the distance between the road and the measurement site. Figure 3 shows a graphical dependence of the level of car noise on the distance to the road at a constant traffic flow rate of approximately 3600 vehicles per hour.
As the distance from the road to the noise measurement site increases, the equivalent sound level gradually decreases. The dependence has a linear trend and is described by equation (3) with the determination coefficient R 2 =0.967. L eq =−0 . 491⋅l+78 .32 (3) Where: Leqv -measured equivalent sound level, dBA; l is the distance from the road to the measurement site, m.
At a distance of up to 35 m from the road, the value of the noise characteristic of the traffic flow significantly exceeds the maximum permissible sound level of 55 dBA. That is, not only the direct participants in the road traffic: pedestrians, drivers, passengers of vehicles, but also residents of adjacent territories are exposed to the negative impact of traffic noise.
To reduce noise pollution caused by vehicles in the studied sections of the road network, the following measures can be proposed:  Application of noise barriers.  Improving infrastructure, using low noise road surfaces.  Optimization of road traffic, speed control, removal of noise sources outside the residential area. The most radical way to reduce the acoustic pollution of an urbanized area by vehicles is to reduce the noise at the source, that is, to improve the design of vehicles. However, this method requires significant financial costs and a long time for implementation.

Conclusion
The sections of the road network of the city, where a high level of accidents is noted, are also characterized by high values of car noise. The dependence of the noise characteristics of traffic flows on the total intensity and structure of flows has been studied. With a small proportion of trucks in the traffic flow, the equivalent sound level is most determined by the overall intensity of the flow and the number of cars in it (the correlation coefficients are 0.975 and 0.947, respectively).
A study of the dependence of automobile noise on the distance from the road showed that the equivalent sound level exceeds the maximum permissible level for any measured value of the flow intensity and distance from the road up to 35 m.