Determination of safe distance between roadway and school buildings to get acceptable school outdoor noise level by using noise barriers

Transcription

1 ARTICLE IN PRESS Building and Environment 40 (2005) Determination of safe distance between roadway and school buildings to get acceptable school outdoor noise level by using noise barriers Yasar Avsar, M. Talha Gonullu Yildiz Technical University, Environmental Engineering Department, Besiktas, Istanbul, Turkey Received 15 April 2003; accepted 25 October 2004 Abstract Noise nuisance caused by road or highway depends on three main reasons; (1) type, speed and number of vehicles, (2) road surface structure sort and (3) characteristics of buildings and number of inhabitants. School buildings are often subjected to higher outdoor noise levels. Hence intelligibility of lessons by students is decreased. This study deals with relations between vehicle speeds and noise levels. Following the road study, without using any noise propagation processes, convenient school building roadway distances were searched according to possible roadway traffic loads, number of lines and vehicle speeds. In this course, school building road distance, barrier types and their arrangements, road surface types and vehicle speed limitations were offered. r 2004 Elsevier Ltd. All rights reserved. 1. Introduction Noise caused by traffic is the nuisance that is most often cited by roadside residents. School administrations and students living in the proximity of roadways will increasingly perceive noise problems. The effect of environmental noise on growing children has become one of the most important problems, because the personality, mentality and physique of children are being formed particularly at this early age. According to the some of the studies, students performance and behaviors can be changed both in high noisy ambience and quiet ambience [1]. The higher outdoor noise causes the higher indoor noise in classrooms. Disturbance from the outdoor noise is increased in hot seasons in the classrooms, especially when the windowpanes are open. Avsar et al. [2] dwelt upon an example from many educational buildings in this situation in Turkey. Furthermore, Avsar and Corresponding author. Tel.: (2838); fax: address: avsar@yildiz.edu.tr (Y. Avsar). Gonullu [3] put forward by measurements, that all educational buildings (54 primary and secondary schools and 16 high schools) in Fatih District of Istanbul had an outdoor noise level higher than 55 dba (as L Aeq ). Kurra [4] also investigated the effects of traffic noise on teachers annoyance in three high schools located in some busy areas of Istanbul. In that search, it was found that the correlation coefficient from traffic dose/response was as high as In most countries, noise regulations suggest that the maximum outdoor noise level for educational buildings should be 55 dba (L Aeq ). This means that over 55 dba (L Aeq ) outdoor noise level at the facade of educational buildings will cause a decrease in educational efficiency. By putting forward the adverse effects of higher outdoor noise levels on educational efficiency in schools, which has been stated by earlier studies, this study aimed to develop a discussion medium for a possible distance standardization between school and roadway in case of different types of noise barriers and other noise abatement materials between the noise source (traffic) and receiver (school) /$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi: /j.buildenv

2 1256 ARTICLE IN PRESS Y. Avsar, M.T. Gonullu / Building and Environment 40 (2005) Turkish legislation and standardization related in location selection for an educational building In Turkey, neither regulation nor standard exists that is dealing withthis subject. Only a memorandum from the Ministry of Education describes some structural basis during the project and construction of educational buildings, but this does not contain any noise abatement measure. Hence, this initial study was made to obtain a possible standardization that meets adequate outdoor noise level (L Aeq ¼ 55 dba) in TurkishNoise Control Regulation [5]. This discussion study puts forward some outlined ideas about minimum distances between roadway and school with/without noise abatement facilities as depending on roadway traffic load. On the other hand, some indirect regulations and written rules related in the subject exist. For example, the Turkish Highway Traffic Regulation [6] requires a maximum speed limit of 50 km/hfor urban areas. This regulation also forces drivers to decrease their speed in front of educational buildings and prohibits the use of horns. 3. Some common theories to estimate school roadway interactions In practice, there are so many vehicles on the road at the same time. The total noise level will change depending on car numbers. Normally, eachof the vehicles (except heavy ones) have the same noise level on the road with slight differences. By this assumption, the total noise level of vehicles being at same time on the road can be calculated as total noise level ¼ 10 log 10 ½10 L 1=10 þ 10 L 2=10 þþ10 L n=10 Š; dba; where L 1 ; L 2 ;...; L n are noise levels of different sources (dba). ð1þ By using Eq. (1), calculation results obtained for different vehicle numbers are given in Table 1. Inthe table one car is thought of as one noise source and two cars as two noise sources. The cars noise levels were considered to have the same noise level. So, when there is more than one noise source, the sum of the noise levels in ambience was calculated as given in Table 1 logarithmically. The selection of location for a school building and especially the desired distance between school and roadway are important factors for propagated outdoor noise level. Therefore, all schools must be constructed at an appropriate distance from the roadway to obtain an acceptable outdoor noise level. The location of a school area is determined by considering traffic noise propagation through distance. As is known, traffic noise is a type of linear source and its noise value decreases 3 dba withthe distance doubling. Hence, traffic noise propagation as geometrical spreading only can be stated using [7] db ¼ db 0 10 log d ; (2) d 0 where db ¼ noise level at receiver (db), db 0 ¼ noise level at source (db), d ¼ distance between source and receiver (m) and d 0 ¼ distance from measurement point to source (m). 4. Test driving studies with a car Traffic noise is related to vehicle speed. The higher the vehicle speed, the higher the noise. To determine vehicleoriginating noise, experimental studies were carried out for a variety of vehicle speeds. The road used for test drives was asphalt cement and on a smooth surface. All the data of noise levels were obtained using a car marked Renault-Clio. Measurements were performed in accordance withthe TurkishStandards Institute [8].The measurement point was 7.5 m from the roadside and the Table 1 Total noise levels for vehicles having the same noise level

3 ARTICLE IN PRESS Y. Avsar, M.T. Gonullu / Building and Environment 40 (2005) microphone height was 1.5 m. All the noise level measurements were performed by using a sound level meter HD 9018, tri-pod, 1=2 00 condenser microphone and HD 9101 calibrator equipment that correspond to precision class 1 of the standards IEC 942. The HD 9018 sound level meter is a portable measuring instrument, precision class 1 according to standards IEC 651 and IEC 225, precision class 2 according to standard IEC 804, complete withoctave filter witha central frequency from 16 Hz to 16 khz. The wide dynamic range of the instrument is divided into six ranges of 50 db, eachat a distance of 20 db from the other. Two microphones were settled on the right and left sides of the test road. Measuring noise values were taken by the sound level meter when the car moved a 20-m road distance to the C C direction from the A A alignment to the B B line [9]. This test process illustration is given in Fig. 1. Measurement test-driving data obtained for only one car are given in Fig. 2. The noise data were measured as Microphone I A B 7.5 m 10 m C C 7.5 m 10 m B Microphone II Fig. 1. Measuring driving noise for the test study. A the time-averaged level (L Aeq ) by using the sound level meter at a 1000 Hz central octave band. According to the test results, a vehicle at 20 km/h speed causes a 55.1 dba (L Aeq ) noise level as can be seen from Fig. 2. It means that even the least vehicle speed (20 km/h) causes higher noise levels than limit outdoor noise level required for educational buildings. At a 50 km/hspeed limit in an urbanized area, a car causes about 63 dba of noise. All these data indicate that a roadway should never pass near an educational building. 5. Noise level calculations for roads with multiple vehicles The distance required between school and roadway will change, obviously depending on traffic load. In general, roads have at least two or three lines in only a direction in the cities. By means of data in Fig. 2 and Eq. (2), minimum required distances between school and roadway were obtained as shown in Fig. 2, according to vehicle speeds and roadway line numbers, in order to meet the 55 dba limit outdoor value. After establishing noise level and vehicle speed relations in Fig. 2 by a measuring technique, Fig. 3 was formed by using Eq. (2) with calculation assuming no heavy vehicles on the road. A two-sided road with one lane was thought of as two noise sources (cars), a two-sided road withtwo lanes was thought of as four noise sources, and a two-sided road with three lanes was thought of as six noise sources at the same time. Fig. 3 contains roadways having one, two and three lanes for two-sided roads, and these roadways do not have any noise abatement barriers between traffic and school. As can be observed from Fig. 3, a roadway witha 50 km/hmean vehicle speed and 1 lane for two-sided road should be at least 55 m distant from a school wall. The minimum required distances for two and three lanes for two-sided roads are LAeq, dba y = Ln(x) R 2 = Vehicle speed, km/h Fig. 2. Noise data obtained for different vehicle speeds at 7.5 m distance from the road border.

4 ARTICLE IN PRESS 1258 Y. Avsar, M.T. Gonullu / Building and Environment 40 (2005) School-roadway, m Line 2 Lines 3 Lines Vehicle speed, km/h Fig. 3. Minimum school road distances as depending on roadway lane numbers and vehicle speeds. about 111 and 175 m, respectively, without noise abatement barriers. These distances are quite high to meet for a common city school. These data put forward the importance of a noise abatement barrier for such sensitive areas. 6. Noise abatement levels with natural and artificial barriers To get a 55 dba outdoor noise level for a school building, some of the following noise control barriers can be used, suchas, natural barriers as vegetation, artificial barriers as wooden or concrete walls, and surface coatings described as porous asphalt on the roadway. Some of the recent studies show that roadway noise level can be decreased by 5 dba using a 30 m depth of high trees having wide leaves in a straight line from the roadway source to the receiver [10]. Although natural barriers cause lower noise abatement, their effectiveness can be increased in combination withartificial noise barriers. In addition, as expected, the increasing row number of natural barriers also causes higher noise abatement. The reasons for preference of the natural barriers are its naturalness, esthetic considerations and cheapness. In addition to improving the barrier from an esthetical viewpoint, natural barriers are also useful because they absorb emissions: particulates and heavy metals from traffic. The noise abatement values and advantages/disadvantages of some natural barrier sorts are given in Table 2. Table 2 gives quite a clear idea about embankment effectiveness on noise abatement, although trees and bushes are taller than bush on embankment. Artificial barriers suchas a 2 m concrete wall obtain on average 10 db noise abatement [11]. Generally, the effectiveness of noise abatement barriers can be explained briefly as follows: Noise reduction up to +5 dba was obtained with vegetation, depending on the species, height, intensity and position of the plantings. A 30 m depth of vegetation with enough height/density and parallel to the road decreases the traffic noise value easily by þ5 dba: If the length of parallel vegetation planted on the road is 60 m, noise reduction reaches up to þ10 dba: Noise reduction up to þ3 dba can be obtained at a 50 m depth and a 1.5 m height of dense bushes planted on the roadway [11]. 7. Noise abatement levels with a porous roadway pavement Another alternative suggestion for noise abatement, which is different from barrier measures, is to change the road surface materials. The mechanisms generating tyreroad noise are strictly dependent on the surface characteristics of the pavement. According to the OECD Report, some road surface material types and corresponding noise levels are given in Table 3. Table 3 shows the noise levels measured at the roadway when the vehicle speed is 80 km/h. It can be seen that porous asphalt pavements (also called draining or soundabsorbing) are the most valid from the acoustic standpoint.

5 Table 2 Role of natural barriers on noise abatement [11] ARTICLE IN PRESS Y. Avsar, M.T. Gonullu / Building and Environment 40 (2005) Species Dimension (m) Acoustic function Noise abatement (dba) ðþþ: Advantage ð Þ: Disadvantage Trees and bushes L: at least 10 Absorptive 3 4 ðþþ: Good esthetic appearance and decreases emissions. H: 8 9 ð Þ: Limited noise abatement Bushon embankment L: Absorptive (+): Good esthetic appearance and Reflective effective on noise abatement. H: 3 4 ð Þ: Needs wide spaces Porous asphalt Absorptive 5 ðþþ: Practical ð Þ: Limited noise abatement One row of vegetation consisting of tall and dense trees being parallel to the road in 30 m width Absorptive 5 ðþþ: Good aesthetic appearance ð Þ: Limited noise abatement Two rows of vegetation consisting of tall and dense trees being parallel to the road in 30 m width Absorptive 10 ðþþ: Good esthetic appearance and decreases emissions Establishment of a 2 m height concrete garden wall before the road Absorptive Reflective 10 ðþþ: Effective on noise abatement ð Þ: Costly, not esthetic 50 m length and 1.5 m height bushes on a row and 10 m width Absorptive 2 ðþþ: Good esthetic appearance ð Þ: Limited noise abatement Table 3 Typical ranges of tyre/road noise levels according to the type of road surface [11] Type of road surface Traditional bituminous mix overlay Chipped bituminous concrete Cold bituminous mixes High-performance microcarpet Single-course surface dressing Double-course surface dressing Porous asphalt Cement concrete Concrete set paving Noise level (dba) As can be seen from Table 3, porous asphalt is the first road pavement technique identified as a low-noise surfacing, and acoustical researchhas been devoted mainly to optimizing its effectiveness. The average noise abatement is þ5 dba when porous asphalt is used as a road surface material. Ergun [12] emphasized that porous road pavements caused on average 5 dba abatement of noise originating from traffic current. 8. Minimum distances between road and school with noise abatement measures To obtain acceptable outdoor noise levels on a school building facade, one barrier or a combination of different types of noise barriers should be used. According to the TurkishHighway Traffic Regulation [6], th e maximum vehicle speed value is 50 km/h in cities. At this speed, vehicles cause a 64 dba noise level from Fig. 2. Inthe studied area, roadways have two sides with one, two and three lanes. It means that there are two, four and six noise sources at the same time and same alignment when the roadway lanes are one, two and three, respectively. In this case, while one vehicle causes 64 dba noise, two, four and six vehicles cause 67, 70 and 72 dba noise, respectively, by calculating from Table 1. Table 4 contains minimum distance values calculated for different options of the measures and traffic loads by using the noise attenuation level of different noise barriers given in Table 2. This table gives an idea about the effectiveness of these measures. It can be seen that a 2 m high concrete wall and a surrounding embankment of 3 4 m height give quite effective levels of abatement. Roadway noise can travel around the end of a barrier and reach the receiver if

6 1260 ARTICLE IN PRESS Y. Avsar, M.T. Gonullu / Building and Environment 40 (2005) Table 4 Safe outdoor distances for different noise abatement measure options Class Abatement measures School-road with 2-directed distances (m) and outdoor noise levels, (dba) 1 Line Noise value 2 Lines Noise value 3 Lines Noise value A No noise preventive precaution Trees and bushes (L: at least 10 m, H: 8 9 m) B Porous asphalt (5 dba abatement) C One row of vegetation consisting of tall and dense trees being parallel to the road in 30 m width D Two rows of vegetation consisting of tall and dense trees being parallel to the road in 30 m width 2*C E Establishment of a 2 m height concrete garden wall before the road F Cþ E G Aþ C þ E ¼ A þ F H Bushon embankment (L: m, H: 3 4 m, 10 m) I 50 m length and 1.5 m height bushes on a row and 10 m width) J Bþ I the barrier is too short. A rule-of-thumb to ensure that the wall kind of barrier is long enough to avoid this undesirable effect is that the barrier should extend four times as far in eachdirection as the distance from the receiver to the barrier. Other choices and combinations of these enhance the level of total abatement. 9. Conclusions This initial analysis evaluating present school establishment rules in Turkey puts forward a total disregard in this matter; it also suggests having an appropriate outdoor noise level. By means of noise data obtained from a realized test roadwork, noise data derived for different traffic load levels by calculations showed that even one lane in a direction gives a noise level higher than 55 dba. Hence some alternative noise abatement measures were examined to solve the problem that results from not leaving enoughempty area around a school. For this restrictive reason, using noise abatement barriers or other noise protective materials is very necessary. It is possible that concrete walls of appropriate height and lengthnear the roadway, enoughembankment with bushes between the traffic current and school, and also a combination of noise barriers suchas vegetation and concrete walls or porous road pavements will decrease the outdoor noise level to less than 55 dba in schools. Acknowledgements References [1] Sargent JW, Gidman MI, Humphreys MA, Utley WA. The disturbance caused to school teachers by noise. Journal of Sound and Vibration 1980;70(4): [2] Avsar Y, Gonullu MT. Outdoor noise level at Yildiz Technical University, Istanbul Turkey. Journal of the Canadian Acoustical Association, 2001; [3] Avsar Y, Gonullu MT. A map preparation for outdoor noises of educational buildings in FatihDistrict of Istanbul. International Symposium on Noise Control & Acoustics for Educational Buildings, May, Yildiz Technical University, 2000; Istanbul/Turkey. pp [4] Kurra S. Results of a pilot study about teacher s annoyance relative to noise exposure in three high schools in Istanbul. International Symposium on Noise Control & Acoustics for Educational Buildings, May, Yildiz Technical University, 2000; Istanbul/Turkey. pp [5] TurkishNoise Control Regulation [6] Highway Traffic Regulation numbered and dated Pedestrian and School Passageways, Rule number is 2918, Ankara/Turkey. [7] Cheremisinoff PN, Young RA. Pollution engineering practice handbook [8] TurkishStandards Institute. Urbanized area roads-determination of traffic noise and its precautions. Standard #:10713, February, [9] TurkishStandards Institute. Guide to measure of noise level of highway vehicles. Standard #: 2214, December [10] Highway traffic noise in the united states problem and response, Department of Transportation Federal Highway Administration, April, 2000, USA. [11] Road transport research, Roadside noise abatement, Report prepared by an OECD Scientific Expert Group, [12] Ergun M. Porous road pavement as a new solution to the noise problem resulting from urbanized transportation at touristic regions. Transportation symposium, Istanbul, Turkey The authors thank the headmasters of all the high schools in Fatih district for their friendly and scientific approachto our noise measurement field study.