Environmental Monitoring and Assessment (2006) 123: 413Ð430 DOI: 10.1007/s10661-006-1494-6 c Springer 2006

ASSESSMENT OF TRAFFIC NOISE POLLUTION FROM 1989 TO 2003 IN CITY

GUOXIA MA1,2, YUJUN TIAN3,∗, TIANZHEN JU4 and ZHENGWU REN5 1Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sources; 2Graduate School of Chinese Academy of Sources, Beijing, 100101; 3Department of Geography, Teachers College, Shihezi University, Xinjiang 832003; 4College of Geography and Environmental Science, Northwest Normal University; 5Environmental Monitoring Station of LanZhou City, LanZhou, 730070 (*author for correspondence, e-mail: [email protected])

(Received 25 February 2005; accepted 28 July 2005)

Abstract. On the basis of the continuous traffic noise data observed at 142 sites distributed in 52 roads from 1989 to 2003, the characteristics of traffic noise and effect factors were analyzed through traffic noise indices, such as Lep, L10, L50, L90, TNI, and Pn. Our findings allow us to reach a number of conclusions as follows: Firstly, traffic noise pollution was serious, and its fluctuant characteristic was obvious, resulting in a great intrusion to public in Lanzhou City during last 15 years. Secondly, traffic noise made a distinction between trunk lines and secondary lines, west-east direction roads and north-south direction roads. Thirdly, spatial character and time rule of traffic noise were obvious. In addition, traffic volume, traffic composition, road condition, and traffic management were identified as the key factors influencing traffic noise in this city.

Keywords: traffic noise, noise assessment, effect factors, prediction indices, Lanzhou City

1. Introduction

Road traffic is a major source of noise in urban areas with far-reaching and wide- range effect to human. It produces disturbance and inversely impacts more than other forms of noise (Dix, 1981; Zannin et al., 2003; Joel Manoel et al., 2004). Urban traffic noise impact assessment has thus become an active environmental acoustics domain. Brown studied the choosing principle of measurement sites, analyzing methods and evaluation indices of traffic noise in different urban ar- eas (Brown et al., 1987). By studying the total characteristics of traffic noise and its time distribution in Pamplona City of Spain, Arana found the diurnal equivalent sound levels measured in 185 different locations evenly distributed around the Pamplona exceeded 65 dB(A) in 59% of the locations. Moreover, the social survey carried out in five representative areas showed that noise annoy- ance was a serious problem to many residents (Arana and Garcia, 1998). On the base of large numbers of survey data, similar findings have been evaluated in Singapore, Malaysia, Japan, respectively (Heng, 1979; Kono, 1982; Sy, 1985; Nulty, 1987). 414 G. MA ET AL.

TABLE I Ratio of above criterion cities of traffic noise in monitoring cities of

Years 1989 1991 1992 1993 1995 1996 1997 1998 1999 2000 2001

Ratio of above 94 66.6 92.8 81.82 71.4 82.2 50 43.9 41 53.3 48.7 criterion cities

It has been reported that road traffic noise in developing countries has not yet been recognized as a major problem (Fuchs, 1975). With the increase of population and automobiles, developing countries have been aware of traffic noise pollution step by step. Work carried out in Greater Cairo, indicated noise levels in the city were higher than those set by the Egyptian noise standards and policy to protect public health in residential areas. Simultaneously, a social survey showed that 73.8% of respondent residents were highly or moderately irritated by road traffic noise (Ali et al., 2002). Equivalent noise levels (LAeq) were considerably reduced after restrictions were introduced (Ali et al., 2003). Road traffic noise is the main environmental pollution bothering people in Nigeria (Menkiti, 1998). M.U. Onuu conducted the road traffic noise at over 60 sites in 8 cities in South-Eastern Nigeria using field measurements and psychological survey (Onuu, 1996, 2000). China, as a developing country, traffic noise pollution occurs seriously in its urban areas. According to surveying results published by Environmental Protection Agency of China, ratio of noise source emitted from traffic contributed about 35, 32.7, 31, 30.2, 27, and 28.9% in all monitoring cites from 1989 to 1994, respectively. Further, Table I indicates cities exceeding the traffic noise permissible criterion of 70 dB(A) accounted for high proportion in monitoring cites from 1989 to 2001(EPA of China, 2001). Lying in the middle of Basin, Lanzhou is a typical narrow zonal city with long extension to west and east. The main part of the city centralizes in Yellow River Basin. The downtown area covers 320 km2. Mean length of west-east is about 45 km, and width of north-south is from 2 km to 8 km. The tightness of city1 is 0.196, and diameter of road network is about 45.56 km. It is 0.441 and 0.804 lower than that of quadrate city and ring city, but diameter of road network is 22.87 km and 35.55 km higher than them under the same condition, respectively (Li, 2002). Narrow zonal network diameter makes traffic jam is more serious than that of ring city. Furthermore, Lanzhou is one of the important traffic hubs and freight transfer stations in northwestern China. Large numbers of transfer vehicles congesting in the downtown make for the big pressure of road and outstanding traffic noise pollution. Previous research on evaluation of urban traffic noise mainly focused on polluted extent and annoyance in short time and hardly reflected the spatio-temporal change of traffic noise pollution in long time. In this study, by using time serial data of traffic noise from 1989 to 2003, the authors highlight in particular the historical ASSESSMENT OF TRAFFIC NOISE POLLUTION FROM 1989 TO 2003 IN LANZHOU CITY 415 evolvement process, spatial characteristics, and effective factors of traffic noise pollution in particular.

2. Study Area

Lanzhou occupies an area of 1.31 × 104 km2, including Qilihe , Chengguan District, , , as well as , , Yundeng County. For the study, Anning District, , Chengguan District and Xigu District were selected, almost covering the whole downtown. Road area of Chengguan District is 94.69 × 104 m2 with road length of 5.79 × 104 m; of Qilihe District is 56.24 × 104 m2 with road length of 2.58 × 104 m; of Xigu District is 61.99 × 104 m2 with road length of 3.45 × 104 m; of Anning District is 19.15 × 104 m2 with road length of 0.69 × 104 m. 142 measuring sites were monitored on 52 roads as shown in Figure 1. Total length of survey roads is 125.35 km, including 76.74 km trunk roads and 48.61 km secondary roads.

3. Data and Methodology

In order to analyze the spatio-temporal change characteristics of traffic noise pol- lution, the sequential data of 142 measurement sites on 118 road segments of 52 main roads from 1989 to 2002 were gained from Environmental Monitoring Station of LanZhou, including traffic volume, equivalent serial sound level (Leq), statistic sound level (L10, L50, L90). Moreover, to research traffic noise distribution, effect factors and traffic noise pollution at present, the authors monitored 142 measure- ment sites as same as those of Environmental Monitoring Station did in September and October of 2003. Noise measurements were performed at chosen sites as fol- lows. Followed China National Standard (CNS), GB3222-94 (Measurement of Urban Environment Noise), noise measurements were conducted at 8Ð11 a.m. and 2Ð 4 p.m. for two months when there was no rain or wind. All measurement sites were placed at the edge of road about 50 m away from crossing. A noise statistic apparatus of AWA6218 with accuracy of 0.7 dB(A) was set at a height of 1.2 m above the ground level to measure Leq, L10, L50 and L90. The apparatus was calibrated prior to each measurement using ND9 calibrator with accuracy of 0.3 dB (A). According to CNS, GB1496-79 (Methodology of Surveying Traffic Noise of Individual Vehicles), vehicles can be classed into three types. (1) Heavy vehicles with three or more axles and designed for the transportation of cargo with weight more than 3500 kg. (2) Medium vehicles with two axles and six wheels for the transportation of cargo with weight less than 3500 kg, and buses carrying more than 30 passengers. (3) Light vehicles with two axles and four wheels for transportation of cargo with burdening weight less than 1250 kg, and buses carrying less than 30 416 G. MA ET AL. . Sketch map showing spatial distribution of 142 measure sites on 52 roads in Lanzhou City. Figure 1 ASSESSMENT OF TRAFFIC NOISE POLLUTION FROM 1989 TO 2003 IN LANZHOU CITY 417 passengers. The number of them passed by the observer during the time interval of each measurement was counted for 20 min by three men. Average speed of vehicles, road surface, road width, and transit vehicles were recorded.

4. Prediction Indices

It is difficult to choose right indices to evaluate the extent of traffic pollution, variety, and its impact on people and society as the prediction indices measured by apparatus just describe the physical attribute to acoustical system, but they can not reflect the subjective response and the physiological and psychosocial harm extent to public. In order to predict the physical attribute of traffic noise and subjective response of people, traffic noise index (TNI), noise pollution index(Pn) and road length of different Leq were adopted, in addition to the common indices of Leq, L10, L50, L90.

(1) The equivalent continuous sound level (Leq) is the evaluation value of public reflection on the base of average energy level. The value of 70 dB(A) is defined as threshold of over criterion. (2) Statistic sound level (L10, L50, L90) is the level exceeding for a particular percentage of the total time. L10 describes the mean peak value level; L50 describes average of traffic noise; L90 corresponds to the background noise level in the absence of nearby noise sources. (3) Traffic noise index (TNI) describes the noise level and fluctuant characteristic. It has good relativity with subjective response of public and can be used to evaluate disturbance of a mass of traffic volume to public. Value of 74 dB(A)is defined as threshold of over criterion.

TNI = 4 × (L10 − L90) + L90 − 30

(4) Road length of different equivalent sound level evaluates the pollution extent and range by calculating the road length with 3 dB(A) intervals. (5) Noise pollution index (Pn): Pn = Leq/Lb

Where, Lb is baseline data taking 75 dB(A) of high annoyance outdoors as limit. With respect to Table II, noise radiated energy level can be checked out.

5. Evaluation Results

It can be seen from Figure 2 that traffic noise pollution was serious on roads in Lanzhou City during the last 15 years. The years that Leq exceeded the permissible 418 G. MA ET AL.

TABLE II Grade on noise radiated energy

Grade Grade description Pn Leq (dB(A))

I No noisiness <0.6 <45 II A little noisiness 0.60Ð0.67 45Ð50 III Noisiness 0.67Ð0.75 50Ð56 IV Rather noisiness 0.75Ð1.0 56Ð75 V Very noisiness >1.0 >75

Figure 2. Annual variety of characteristics of traffic noise in Lanzhou City from 1989 to 2003. levels 70 dB(A) accounted for 35.7% of all years. Annual mean value of Leq that did not exceed criterion was between 69.11 dB(A) and 70 dB(A). Annual mean value of L10 was above 71 dB(A), and Pn was in excess of 0.92. That is, traffic noise belonged to rather noisiness field in terms of Table II. TNI exceeded seriously, and annual change was remarkable. Except for the year of 1998, TNI went beyond criterion of 74 in other 14 years. It indicates traffic noise changes smart in per unit of time, and disturbs public intensively. According to distribution of Leq and definition of Leq (when Leq adds 3 dB(A), noise radiated energy adds to one time). Leq was classified into seven types with 3 dB(A) intervals. Then road length of seven kinds of Leq was calculated to evaluate pollution extent and scope, as can be seen in Table III. The longest road of annual traffic noise was at the range of 69 dB(A) to 72 dB(A), suggesting the noise pollution level of most of road segments was serious during past 15 years. Traffic noise pollution was more serious on trunk lines than on secondary lines during past 15 years. Computing difference of evaluation indices between trunk lines and secondary lines, the result shows the difference of Lep and L90 was positive in Figure 3. Mean difference value of Leq was 11.88 dB(A), and maximum value reached 15.87 dB(A). The difference of evaluation indices trended to reduce after 1997. The length of secondary lines was longer than that of trunk lines at range of low noise. Mean value of road length on secondary lines was 3.33 times as long as on trunk lines when Leq was less than 63 dB(A) during past 15 years. From what ASSESSMENT OF TRAFFIC NOISE POLLUTION FROM 1989 TO 2003 IN LANZHOU CITY 419

TABLE III Road segments distribution of different sound level in Lanzhou City from 1989 to 2003

Field of sound level Leq(dB(A)) trunk line (km)

Year ≤63 63Ð66 66Ð69 69Ð72 72Ð75 75Ð78 >78

1989 2.1 20.18 26.71 42.75 23.74 29.85 0 1990 0 0 33.91 47.14 38.34 5.96 0 1991 0 3.43 41.02 68.81 9.16 2.944 0 1992 0 13.95 21.41 56.79 28.12 0 5.1 1993 0 0 6.9 31.68 62.03 24.75 0 1994 1.13 0 27.24 65.66 21.48 6.55 3.3 1995 0 3.98 28.13 55.03 30.61 4.67 2.94 1996 0 2.76 11.68 60.68 40.67 9.57 0 1997 0 2.64 49.31 55.8 17.4 0 0 1998 0 7.53 49.72 53.95 12.82 1.34 0 1999 0 2.64 57.64 59.66 5.41 0 0 2000 0 0 49.07 61.99 10.12 4.17 0 2001 0 7.25 34.77 66.2 36.02 0 0 2002 0 2.96 24.18 39.62 9.98 0 0 2003 0 2.03 24.24 40.60 9.9 0 0

Figure 3. Difference of noise evaluation indices in trunk lines and secondary lines in Lanzhou City. have been analyzed, traffic noise pollution centralizes on trunk lines, so mitigation measures for controlling the problem of road traffic noise should be implemented on trunk lines. However, the years in which difference of TNI was negative between trunk lines and secondary lines accounted for 80.0% of total years. That is to say, disturbance of traffic noise pollution to people on secondary line was worse than that on trunk line. 420 G. MA ET AL.

Figure 4. Difference of noise evaluation indices at different directions in Lanzhou City.

Lanzhou City is a typical narrow zonal city. It makes big difference of road network at west-east direction and north-south direction. 62 percent of trunk lines are at west-east direction, accounting for 77.3% of total road length. Moreover, the most of west-east roads directly connect urban border, and many transit vehicles move along these roads. The ratio of transit vehicles is 1.32:1 between west-east direction and north-south direction. There were thirteen years when mean value of Leq at west-east direction was higher than at north-south direction during past 15 years. More importantly, annual Leq of west-east went beyond 69.35 dB(A). The years that Leq exceeded criterion at west-east direction was1.7 times as much as that at north-south direction. The years in which L10, L50, L90 at west-east direction was bigger than that at north-south direction accounted for 85.7, 85.7, 64.3% of total years respectively. By computing evaluation indices difference of west-east direction and north-south direction as shown in Figure 4, the annual change curve of TNI was the strongest and maximal difference reached 9.29. Based on what analyzed, the time of high noise exposed was longer, and the extent of noise disturbance was stronger at west-east direction. Traffic mix stands out in Lanzhou City. Especially, transit vehicles and urban vehicles mix together without transit carriageway. Double-functional roads that take on transit vehicles and urban vehicles distribute periphery of city or west-east roads. Mean width of double-functional roads is 21 m, and total length is 68.79 km; mean width of urban roads is 14 m, and total length is 56.56 km. From the difference of evaluation indices between double-functional roads and urban roads in Figure 5, it is clear that L10, L50, Pn on double-functional roads were higher than on urban roads from 1989 to 2003. Mean Leq and TNI on double functional roads was 1.2 dB(A), 3.41 dB(A) higher than on urban road, respectively. There were thirteen years that Leq exceeded criterion on double functional roads during past 15 years, but just had four years on urban roads. In conclusion, traffic noise on ASSESSMENT OF TRAFFIC NOISE POLLUTION FROM 1989 TO 2003 IN LANZHOU CITY 421

Figure 5. The difference of prediction indices on double function roads and urban roads.

Figure 6. Annual change of prediction indices in four areas during past 15 years. double functional road was more serous than that on urban road, and had long exposure time to disturb public. Figure 6 shows the annual change of traffic noise pollution in four areas dur- ing past 15 years. From 1989 to 1996, annual change of traffic noise pollution was smart and pollution was serious in four areas. There are 5 years that mean value of Leq went beyond criterion in Chengguan District and Xigu District, 7 years in Anning District and Qilihe District. Mean value of TNI exceeded the cri- terion in four areas. From 1997 to 2003, the annual change of prediction indices 422 G. MA ET AL.

TABLE IV Mean evaluation indices in different district of Lanzhou City during past 15 years

District Leq L10 L50 L90 TNI Pn

Chengguan district 70.01 72.26 65.70 60.36 77.96 .93 Qilihe district 70.03 72.84 67.08 60.51 79.82 .93 Anning district 70.26 72.69 66.21 60.44 79.43 .94 Xigu district 69.72 72.31 64.79 58.53 83.64 .93

trended to decrease except for TNI which exceeded the criterion in all areas. How- ever, traffic noise still kept in high pollution level with mean value of Leq of 69 dB(A). Table IV demonstrates the spatial character of traffic noise in four areas during past 15 years. Traffic noise pollution is so bad that all of them are rather noisiness by index Pn. The sequence of Leq is Anning District > Qilihe District > Chengguan District > Xigu District; the sequence of L10 is Qilihe District > Anning District > Xigu District > Chengguan District; the sequence of TNI is Xigu District > Anning District > Qilihe District > Chengguan District.

6. Factors Analysis

6.1. TRAFFIC VOLUME

Traffic volume is one of factors to affect traffic noise pollution. In 1989, annual traffic volume was 397.75 vehicles/h and it reached 1522.01 vehicles/h in 2003, annual increasing traffic volume was 94.95 vehicles/h. In the light of experience of urban roads, traffic volume of 400 vehicles/h is saturation capacity on single carriageway. About 48.0% of road segments exceeded the criterion in Lanzhou. Most of them were west-east direction and double-functional roads. Analyzing the relationship of traffic volume and traffic noise, the results indicate that traffic volume have correlativity with Leq, L10, L50, L90, TNI, and Pn as shown from Figures 7Ð12, especially, it has fair positive correlativity with L50, L90, and has negative correlativity with TNI which indicates that undulation of traffic noise is obvious and has strong disturbance to people in low traffic volume. Moreover, traffic volume of 1000 vehicles/h is the dividing value in Lanzhou City. Namely, when traffic volume is less than 1000 vehicles/h, all prediction indices increase with traffic volume adding. However, when traffic volume goes beyond 1000 vehicles/h, the change trend of them keeps stabilization. It means noise level trends to rise with traffic volume increasing, however, when traffic volume gives rise to some particular value, noise level will keep stabilization. ASSESSMENT OF TRAFFIC NOISE POLLUTION FROM 1989 TO 2003 IN LANZHOU CITY 423

Figure 7. Relationship between traffic volume and Leq.

Figure 8. Relationship between traffic volume and L10.

Figure 9. Relationship between traffic volume and L50. 424 G. MA ET AL.

Figure 10. Relationship between traffic volume and L90.

Figure 11. Relationship between traffic volume and TNI.

Figure 12. Relationship between traffic volume and PN. ASSESSMENT OF TRAFFIC NOISE POLLUTION FROM 1989 TO 2003 IN LANZHOU CITY 425

TABLE V The correlation coefficients between vehicles composition and noise indices

Leq L10 L50 L90 TNI

Ratio of heavy vehicles (%) 0.360∗∗ 0.411∗∗ 0.063 −0.236∗ 0.649∗∗ Ratio of medium vehicles (%) 0.014 0.104 0.223∗ 0.109 0.056 Ratio of light vehicles (%) −0.315 −0.415∗∗ −0.228 0.045 −0.469∗∗ ∗∗Correlation is significant at the 0.01 level; ∗Correlation is significant at the 0.05 level.

6.2. TRAFFIC COMPOSITION

Traffic noise changes with traffic composition variety. For noise prediction purpose, traffic composition is generally classed into three types as what have been defined. In general, traffic noise level is: heavy vehicles > medium vehicles > light vehicles under the same condition. In the light of research of authors in 2003, the ratio of light vehicles exceeded 34.6% on all roads. Among them, the road segments that ratio of light vehicles was between 60% and 80% accounted for 50.4%, the road segments with ratio of light vehicles between 80% and 90% accounted for 24.4%, and the road segments that ratio of light vehicles went beyond 90% accounted for 9.2%. Table V indicates the correlation coefficients between vehicles composition and prediction indices. It is clear that the ratio of heavy vehicles has the most remarkable impact on traffic noise. The ratio of heavy vehicles has the positive correlativity with TNI, L10, Leq from Figures 13Ð15, and Light vehicles have the negative correlativity with TNI, L10 in Figures 16 and 17. The speed of vehicles is between 30 km/h and 50 km/h on all measurement roads of Lanzhou. The relation between the speed of vehicles and the noise levels is well known, less than 50 km/h, the engine noise dominates and above 50 km/h, the tie noise becomes the dominant noise source (Rylander et al., 2002). While for small vehicles the major part of

Figure 13. Relationship between rate of heavy vehicles and TNI. 426 G. MA ET AL.

Figure 14. Relationship between rate of heavy vehicles and L10.

Figure 15. Relationship between rate of heavy vehicles and Leq. noise emitted is at the pavement-tire interface, heavy vehicles emit much of their noise at the engine level. These indicate that the increase in traffic noise is more adversely affected by heavy vehicles than by increase in number of other kind vehicles in Lanzhou. This result is similar to that reported by Joel Manoel et al. (2004) in the city of Florianopolis of Brazil and Mutasem (2002). Tractors were the dominant noise source in Anning District in the early time. Table VI shows the evaluation indices decreased with quantity of tractors declining

TABLE VI Effect of reducing tractors to evaluation indices (Anning west road)

Leq (dB(A)) L10 (dB(A)) L50 (dB(A)) L90 (dB(A)) TNI (dB(A)) Pn (dB(A))

1990 71.2 75 68 59 77.8 0.949 1991 66.4 70 65 57 64.6 0.885 Difference 4.8 5 3 2 13.2 0.064 ASSESSMENT OF TRAFFIC NOISE POLLUTION FROM 1989 TO 2003 IN LANZHOU CITY 427

Figure 16. Relationship between rate of light vehicles and TNI.

Figure 17. Relationship between rate of light vehicles and L10. from 50 vehicles/hour to 30 vehicles/hour on Anning west road. Lanzhou City, as one of the important traffic hubs, has large numbers of transit vehicles contributing to traffic noise. Furthermore, lack of special transit carriageway makes transit vehicles and urban vehicles mix together, which almost were big vehicles. Phenomenon of horns use is serious, and the time of transit vehicles stay is long.

6.3. ROAD CONDITION

It is also recognized that road condition is one of the major factors to affect traffic noise. Road condition often involves in road gradient, road surface texture, road width, flyover, barrier and shape of street. In view of Yellow River traversing the whole downtown as shown in Figure 1, road gradient is one of the important factors to affect traffic noise on west-east roads, such as Xinxiao North Road, Anning East Road, Langongping Raod. In such ways that vehicles driving up have to slow down, producing the “Slope Effect”, with a consequent noise rise, L10, Leq on gradient 428 G. MA ET AL.

TABLE VII Change of noise evaluation indices after widening road on partial roads

Leq (dB(A)) L10(dB(A)) L50(dB(A)) L90 (dB(A)) Width (m) Time of Name widening Before After Before After Before After Before After Before After

Nanchang 1998 67.5 65.7 69.7 69.9 65.8 66.1 63.4 62.8 9 14 road 1998 70.6 70.7 72.5 71.7 68.8 66.9 61 60.9 18 25 road 1998 67.8 68.4 70.5 70.3 65.6 65.1 64.5 60.9 10 32 road Zhongshan 1996 71.5 71.5 73.2 71.2 67 65.6 63 62.1 10 32 road measurement site of Anning East Road was 4.2 dB(A), 3 dB(A) higher than that on planar measurement site of this road. Establishment of pedestrian overbridge or flyover can reduce L10 of 3.5Ð7.6 dB(A), and Leq of 2 dB(A) (Liu, 1986). The quantity of pedestrian overbridges can not meet the need of traffic in Lanzhou City. Pedestrian overbridges were built only on several main road segments. It leads to serious traffic mix, especially on secondary roads, namely mix of people and vehicles, slow vehicles and quick vehicles. What’s more, the shape intersections of “+” accounts for 43%, and “T” is 52% in Lanzhou City, which have weak capability to go shares traffic volume as compare to circle intersections. Before 1996, trunk lines with width about 21.1 m, and the secondary lines with about 11.7 m, the trunk lines were widened to 24.2 m and the secondary roads were 12.4 m since the 1998. Road widening has obvious function to debase the traffic noise in Table VII.

6.4. TRAFFIC MANAGEMENT

Effective traffic management plays an important role in controlling traffic noise. The measure taken by government has active function to control traffic noise in Lanzhou City. Firstly, rickshaws were prohibited to enter downtown and traffic jam and horn use aroused by rickshaws parking at random were ended in 1994. As a result, values of Leq, L10, L50 and L90 was 1.7 dB(A), 1.9 dB(A), 0.7 dB(A), 0.5 dB(A) in 1994 less than in 1993, respectively. Secondly, government carried out measures to 7000 vehicles of minibuses and taxi ran on single or double day to cut down vehicle jam and noise pollution on main roads in1995. Thirdly, horns of motor vehicles have been banned strictly to use in downtown since the spring of 1997. It was one reason that traffic volume increased largely after 1997, but evaluation indices of traffic noise decreased. For example, vehicles in 1998 were 293 vehicles more than in 1997, but Leq and L10 decreased 0.2 dB(A), 0.1 dB(A). Fourthly, in 2001, measure was taken that heavy vehicles must run on road segments of outskirts. Moreover, six periphery ASSESSMENT OF TRAFFIC NOISE POLLUTION FROM 1989 TO 2003 IN LANZHOU CITY 429 passes and nine night passes were set up to prevent transit carts, tractors and farming vehicles from entering downtown. It reduces the ratio of high noise, and has good function to control noise pollution. At the same time, some important roads have been supervised strictly to smooth traffic flow and control vehicles’ speed, such as on Zhongshan Road, Road and Donggang Road. As a result, Leq, L10, L50 and L90 on three road segments were less than before strict management, which decreased 0.7 dB(A), 0.5 dB(A), 1.5 dB(A), 4.9 dB(A) on Zhongshan Road, 0.9 dB(A), 1.8 dB(A), 2.3 dB(A), 5.4 dB(A) on Qingyang Road, and 2.1 dB(A), 1.7 dB(A), 1.2 dB(A), 3.5 dB(A) on Donggang Road.

7. Conclusions

In this study, some traffic indices of Leq, L10, L50, L90, TNI, and Pn are available for evaluating the traffic noise pollution of Lanzhou City from 1989 to 2003. Some major conclusions are obtained as follows.

(1) Noise pollution is serious in Lanzhou City with mean Leq of 69.3 dB(A). There are 35.7% years that Leq exceeded permissible criterion of 70 dB(A). Leq of most of road segments centralizes at range of 66 dB(A) and 72 dB(A). All studied areas belong to noisiness areas. (2) Traffic noise disturbs public strongly as a result of big undulation of traffic in one unit time. Annual L10 went beyond 71 dB(A) and TNI exceeded the criterion of 74 except 1998 during past 15 years. (3) Spatial distribution and annual change of traffic noise pollution is distinct with characteristics of trunk lines > secondary lines, west-east roads > north-south roads, double-functional roads > urban roads. The sequence of Leq is Anning District > Qilihe District > Chengguan District > Xigu District; the sequence of L10 is Qilihe District > Anning District > Xigu District > Chengguan District; the sequence of TNI is Xigu District > Anning District > Qilihe District > Chengguan District. Traffic noise pollution trends to decrease since the year of 1997 because of effective traffic management in Lanzhou.

Note

1. Tightness = urban area/the least circumcircle area.

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