1 Noise monitoring and analysis
In order to know the traffic noise along the highway in detail, in 2000, we monitored the traffic noise from Nanjing to Xinyi section of National Highway 205 and Nanjing to Suzhou section of National Highway 3 12.
1. 1 monitoring description
(1) The measurement time period is selected at three peak traffic hours every day, namely 9: 30 ~10: 30; 16:30~ 17:30; 2 1: 30 ~ 22: 30, continuous monitoring in each period 1 hour;
② Choose a two-lane road with a width of about 15m on the national highway. The measuring point is 0/0m away from the shoulder/kloc-0 and 0/.2m away from the road surface/kloc-0. The terrain near the measuring point is open and flat, without obstacles;
③ The measuring instrument is domestic HS 6280D noise spectrum analyzer, equipped with HS 4782A printer.
1.2 Description of monitoring indicators
Frequency spectrum of octave band noise-can reveal the frequency components of road noise.
Standard deviation. Reflect the fluctuation of noise level during measurement.
Equivalent continuous sound level. Represents the noise level reflected by the energy averaging method during the measurement.
Lmin- the lowest sound level value during measurement.
Lmax- Maximum sound level value during measurement.
L 10, L50, L90- statistical sound level. Represents the noise level that exceeds several percent during the measurement. For example, L 10 = 60dB, which means that the noise exceeds 60dB for 10% of the measurement period. L 10 is equivalent to the peak of traffic noise. L90 is equivalent to the background value of traffic noise. Many countries adopt L 10 as the evaluation quantity of traffic noise.
Noise distribution-Noise distribution measurement can reflect the percentage of energy that produces the total noise value in each sound level segment.
1.3 Statistics of monitoring results
See table 1 and table 2 for the monitoring results of traffic noise in Nanjing-Xinyi section of National Highway 205 and Nanjing-Suzhou section of National Highway 3 12.
1.4 analysis of monitoring results
It can be seen from Table 1 and Table 2 that 90% of the time noise values of National Highway 205 and National Highway 3 12 reach 72.7 dB and 68.3 dB respectively, while 50% of the time noise values reach 79. 1 dB and 85.4 dB, and 10% respectively. It greatly exceeds the provisions of the Reply of the State Environmental Protection Administration (1999) No.46 on Relevant Issues Concerning the Applicable Standards of Environmental Noise in the Environmental Impact Assessment of Highway Construction, and the requirements of 70dB (a) in the daytime and 55dB (a) at night are implemented within the road center line 100m. It is an urgent problem to take necessary noise reduction measures to reduce traffic noise pollution.
2 Harm of traffic noise
Traffic noise interferes with people's normal life and rest, and even affects people's health in serious cases. Such as cardiovascular diseases and endocrine diseases. Noise will reduce learning efficiency and product quality, and even become one of the factors of social instability under certain conditions. In addition, traffic noise will also affect the economic development along the highway. For example, the economic benefits and production benefits of real estate, factories and shopping malls, which are seriously affected by traffic noise, have declined to varying degrees, and the noise also directly affects the land value around the highway. According to statistics, the land price will drop by 0. 08 ~ 1.26% traffic noise increases by 1 db, which is about 0.9% on average. Conversely, reducing the traffic noise level 1 dB is equivalent to 0.9% appreciation of the land along the line, which is a considerable value for the land transfer fee.
3 Analysis of noise reduction measures
In recent years, many countries in the world have taken measures to reduce road traffic noise, such as applying noise-reducing pavements, planting noise-reducing green belts and building noise barriers.
3. 1 noise reduction pavement
For small and medium-sized cars, with the increase of driving speed, the proportion of tire noise in the noise generated by cars is increasing, so it is of great practical significance to build noise-reducing pavement to control traffic noise. The so-called noise-reducing pavement, also known as multi-gap asphalt pavement, is also known as permeable (or drainage) asphalt pavement. It is to lay a layer of asphalt mixture with high porosity on the structural layer of ordinary asphalt pavement or cement concrete pavement, and its porosity is usually between 15 ~ 25%, and some even as high as 30%. According to foreign research data, this kind of pavement can reduce traffic noise by 3 ~ 8 dB compared with ordinary asphalt concrete pavement, depending on the thickness of pavement, service time, service conditions and maintenance conditions.
The advantage of this method is that because of the high porosity of the mixture, it can not only reduce noise, but also improve drainage performance and improve driving safety in rainy days. Limitations are: poor durability, high requirements for aggregate and binder, and easy to block pores after a period of use.
3.2 Planting noise-reducing green belts
The green belt formed by trees and green plants can effectively reduce noise. Planting trees on both sides of the highway is one of the effective measures to prevent traffic noise. Choosing appropriate tree species, planting density and vegetation width can absorb sound waves and reduce noise. At the same time, the green belt can also absorb carbon dioxide and harmful gases and dust, improve microclimate, prevent air pollution, intercept highway drainage, prevent glare and beautify the environment. According to relevant research data, when the width of green belt is greater than 10m, the traffic noise can be reduced by 4 ~ 5dB. This is because 74% of the acoustic energy projected on the plant leaves is reflected in all directions, and 26% is consumed by the microseisms of the leaves. The reduction of noise is closely related to the width, height, location, configuration and plant species of the forest belt.
This method has obvious ecological benefits. The limitations are: it occupies a lot of land and the noise reduction effect in the early stage is not obvious.
3.3 Sound barrier technology
It is a widely used noise reduction method to reduce highway traffic noise by building sound barriers. Noise reduction of sound barrier is mainly through a series of physical reactions such as absorption and reflection of sound waves by sound barrier materials. According to the test, the noise reduction effect of using sound barrier can reach more than 10 dB. According to its structural shape, the sound barrier can be divided into straight wall type and circular arc type; According to the noise reduction methods, it can be divided into absorption type, reflection type and absorption-reflection composite type; According to its materials, it can be divided into: lightweight composite materials, masonry materials and so on. Because of the different types of noise barriers, they have their own characteristics in noise reduction effect, cost and landscape. Therefore, when choosing a sound barrier, we should choose a suitable type of sound barrier according to the sensitivity of the sound receiving point, the local economic situation and the natural environment.
The advantages of this method are land saving and obvious noise reduction. The limitations are: the long-distance sound barrier makes driving feel depressed and monotonous, and the cost is high. If you use transparent materials, it is easy to glare and reflect light, so you should clean them frequently.
4 conclusion
Because the impact of traffic noise on the environment has attracted more and more attention from all walks of life, noise pollution, one of the four major environmental hazards in the world, must be effectively controlled. Judging from the development law of foreign highway construction, when the road network construction forms a scale, the investment in environmental protection will gradually increase. We should see that any noise reduction method at present has certain limitations in technology and shortcomings in use. We should proceed from the actual situation in various places, strengthen environmental protection construction at the same time of highway construction, conduct technical and economic demonstration on noise reduction measures according to engineering practice, and adopt the best noise reduction scheme after comparing and selecting multiple schemes.