Science of the Total Environment 505 (2015) 658–669
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Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv
Low frequency noise impact from road traffic according to different noise prediction methods Elena Ascari a,b, Gaetano Licitra c,⁎, Luca Teti d, Mauro Cerchiai d a
CNR-IDASC, Via Fosso del Cavaliere 100, I-00133 Roma, Italy University of Siena, Via Roma 56, I-53100 Siena, Italy CNR-IPCF, Via Moruzzi 1, I-56124 Pisa, Italy d ARPAT — Settore Agenti Fisici-AVL, Via Vittorio Veneto 27, I-56127 Pisa, Italy b c
H I G H L I G H T S • • • • •
Low frequency noise (LFN) from road traffic is simulated with many mapping methods. The difference between C- and A-weighted levels is analyzed in several scenarios. Values are provided within virtual and real scenarios and for Pisa city center. LFN may increase in mitigated areas according to a new method and the Nord2000. Correct power spectra in methods are paramount in order to use the C–A indicator.
a r t i c l e
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Article history: Received 22 September 2014 Received in revised form 16 October 2014 Accepted 16 October 2014 Available online xxxx Editor: P. Kassomenos Keywords: Noise mapping Standard method comparison Low frequency Annoyance
a b s t r a c t The European Noise Directive 2002/49/EC requires to draw up noise action plans. Most of the implemented solutions consist in using barriers, even if some studies evidenced that annoyance could increase after their installation. This action dumps the high frequencies, decreasing the masking effect on low ones. Therefore, people annoyance and complaints may increase despite the mitigation. This can happen even in pedestrian zones near main roads due to the screening effect of first buildings row. In this paper, the authors analyze the post-operam screening effects in terms of low frequency noise. The difference between C- and A-weighted levels is calculated as annoyance indicator (LC − A). Different methods able to map noise with octave bands detail are tested in order to establish differences in the estimates of annoyance exposure. In particular, a comparison is carried out between data from interim method NMPB 96, its updated version 2008, NORD 2000 and those provided by a customized procedure through ISO 9613 propagation and Statistical Pass By measurements. Test sites are simulated in order to validate each model results through measurements. Results are discussed for real locations in Pisa city center and virtual scenarios in a rising scale of complexity. © 2014 Elsevier B.V. All rights reserved.
1. Introduction The need of a reliable noise prediction method has been pointed out after the two starting rounds of Noise Mapping according to the 2002/ 49/EC Directive. In addition to the difficulties in comparing results of different national methods, the inapplicability of interim method without calibration arises in local contexts. Thus, CNOSSOS-EU methodology has been set up by JRC (Kephalopoulos et al., 2012), on behalf of European Commission, to provide a common methodology. However, this methodology still lacks of implementation in commercial software and of application in legal terms due to the Member States resistance to change, though some software and validation tests were performed. ⁎ Corresponding author. E-mail address: [email protected] (G. Licitra).
http://dx.doi.org/10.1016/j.scitotenv.2014.10.052 0048-9697/© 2014 Elsevier B.V. All rights reserved.
Apart from the potential developments that may come in the future from the EU commission, this paper analyzes mapping methods using also the outcomes of the local LEOPOLDO project (LEOPOLDO). This project was cofounded by Tuscany Region (Italy) and started in 2005 to develop a detailed knowledge of traffic noise and to implement actions including low emission pavements. Its specific goal was to evaluate absorbent and low emission asphalts as a mitigation action by means of different measurement techniques and to assess the most reliable method. One of the most relevant side outcomes of this project is a large database of vehicle emission, measured according to the Statistical Pass By (SPB) methodology (I. O. for Standardization, 1997). This database not only will constitute the base to eventually verify CNOSSOS implementation in Tuscany, but also is suitable at the moment to evaluate accordance between available models and measured noise emission.
E. Ascari et al. / Science of the Total Environment 505 (2015) 658–669
The previous comparisons (Licitra et al., 2011; Ascari et al., 2010) have shown a significant difference between interim method and spectra measured with SPB techniques, especially in low frequency bands. Evaluating correctly the whole spectrum, especially the low frequency emission, is crucial because noise effects as annoyance or sleep disturbance increase with low frequency noise (LFN) predominance (Persson Waye and Rylander, 2001). Furthermore, LFN annoyance may arise at lower sound pressure levels than high frequency dominant noise (in rural areas not so far from highways, behind barriers, inside homes). This means that many mitigation measures, reducing noise energy, may not improve noise quality nor decrease annoyance (Nilsson et al., 2008). In literature, LFN generally indicates a broadband noise with sound energy dominating at 10–250 Hz (Pawlaczyk-Luszczynska et al., 2003; Leventhall et al., 2003): potential sources of LFN are ventilation system, pumps, compressors, diesel engines and transportation vehicles too. In particular, the importance of evaluating the impact of low frequency noise from road traffic is confirmed in several studies and the Dutch study (Schreurs et al., 2008) LC − A maps of the whole Dutch Highway network are presented. Road traffic is largely studied as low frequency source also by Nilsson et al. (Nilsson, 2007; Nilsson et al., 2008; Nilsson and Berglund, 2006). These studies not only underlined that LFN annoyance is reported in several contexts, but they also assert that it is more intensive than noises without dominant low frequency components (Persson Waye and Rylander, 2001). These studies reported how self-assessed annoyance increases also if a barrier is installed due to the turning up of low frequency noise predominance, since high frequencies are dumped by the barrier. The LC − A is the main indicator identified by Nilsson to relate the annoyance rate difference between barrier and non-barrier situations. It was previously used by different authors, particularly by Kjellberg et al. (1997) that also found a relation to correlate the annoyance perceived to this indicator. Furthermore, LFN has objective effects on humans such as permanent hearing threshold shift, behavior, sleep period, task performances and social attitude as monitored in several studies (Alimohammadi et al., 2013; Kaczmarska and Luczak, 2007). Moreover, the participants surveyed within these works reported some concentration problems and annoyance if exposed to low frequency noises during working activities. At the same time these studies also reported improved mental performances due to the increased arousal of participants. All these studies evidenced that LFN could be a source of stress. The importance of being able to predict low frequency is stated in the literature. Instead only few studies reported modeled values and to date there is not enough literature on low frequency mapping accuracy issues. This study identifies the most critical situations which are relevant to have a reliable method to estimate LFN. It also aims to assess in what extent noise maps are able to predict LFN exposure, comparing the outcomes of different methods and highlighting their pros & cons. In addition to the interim method (NMPB 1996), other standard methods available have been calculated as the NMPB 2008 and the Nord 2000. Furthermore, authors developed a simple tool to obtain emission spectra of roads according to LEOPOLDO database using a modelization with ISO9613 linear sources. This experimental method is tested and compared with official methods results. Tests are performed on virtual and real scenarios in a rising scale of complexity, ending with noise maps for Pisa city center (a Tuscany small city used as test case in previous studies). Results point out the LFN contribution according to the difference between C- and Aweighted levels (LC − A), which is considered to be suitable to evaluate annoyance due to a low frequency content also for road noise (Schreurs et al., 2008; Yifan et al., 2008). The aim of this paper is to evaluate the noise levels produced according to different methods in terms of LC − A. A complete LC − A map is reported for Pisa city center. Besides that, the final goal of the ongoing
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study is to provide a tool able to show a correlation between LC − A hot spots, specific position of the building in the urban fabric, annoyance reported and health effects. 2. Methods The comparison of different prediction methods is performed step by step, from simple to more elaborated and real contexts. At first, a comparison of the methods estimates in a free field condition is needed. In this context, A-weighted levels, C-weighted levels and spectra are evaluated for light and heavy vehicles according to all the tested methods. The calibration is carried out for two measurement positions: 1. the first is positioned as the microphone of the measurements campaign of the Statistical Pass By (7.5 m far from central line, 3 m height, according to HARMONOISE methodology Jonasson, 2004), hereafter named R1; 2. the second is positioned at the reference distance of the NMPB interim method (30 m far from central line, 10 m height), hereafter named R2. In order to verify the coherence of the methods to the measurements, a comparison with on site simple measurements is carried out. This test is performed both for measurements of direct noise and in screened situations (behind noise barriers) to verify the accordance of screening formulas provided by methods, i.e. the reliability of mapping models. Then, the differences in screened and more complex urban configurations are tested on ad hoc scenarios, established by JRC for method equivalence check (Paviotti and Kephalopoulos, 2008). Through those simulations, principal differences of methods in terms of LFN will be highlighted. Within JRC proposed scenarios, the city flat scenario has been chosen because it includes several configurations of buildings and barriers, providing enough complexity and, at the same time, having no altitude variations which are beyond the aims of this paper. Finally, noise maps for Pisa city center are analyzed in terms of LFN impact in specific areas. The similarities and differences between methods on these maps are going to underline the challenges of estimating LFN for road traffic. 2.1. Calculation methods All the simulations presented in this paper have been carried out with the software SoundPLAN 7.1. Differences could be found with other noise mapping software (Marsico et al., 2010). All calculations have been done at fixed temperature (10 °C) and humidity (70%), assuming no correction for favorable propagation. Only the first reflection has been taken into account and, if not specified further, a ground absorbing factor of 0.5 and building absorbing coefficient of 0.2 have been considered. The asphalt type depends on the applied method: we have generally chosen the type of asphalt within each method that does not apply correction to the source power level. This solution is in accordance with the local procedure that actually does not implement asphalt correction. Implemented methods with their settings are briefly described in the following. 2.1.1. NMPB 1996 The “Nouvelle Method de Prevision du Bruit” (NMPB 1996 Cetur, NMPB-Routes-96, 2000) is based upon Guide de Bruit (CETUR, 1980) database and it is the official interim method for the implementation of the 2002/49/EC (to be used by those countries which do not have their own standard). It has been chosen by EU commission because it has the advantage of taking into account both frequency propagation and tested meteorological corrections, requirements fulfilled by few other methods. However, the sound power level database is quite obsolete and weighted traffic flows have to be used in many applications to
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urban agglomerations. Moreover, another disadvantage is the use of a constant reference spectrum between 100 Hz and 5 kHz: no speed dependency is estimated and a fixed percentage of heavy vehicles is considered, regardless of the road type and real predominance of heavy vehicles. In fact, setting the amount of heavy vehicles only changes the overall sound power but not the spectrum. In this study, only A-levels and C-levels are reported in order to compare the official standard with other methods: unfortunately, the software does not include spectra export for this specific model. 2.1.2. NMPB 2008 The NMPB 2008 (Dutilleux et al., 2010) improved power level reliability with respect to its previous version, since the old database of the Guide de Bruit has been updated with new power levels. Therefore, light vehicles' flows do not need anymore adaptation in order to calibrate A-Levels. However, the heavy vehicles are still too noisy for urban environment (heavy traffic flows should be halved as shown in the following paragraphs) and it uses still a constant reference spectrum. As in the previous version, this characteristic makes French models generally unsuitable for the evaluation of the low frequency content, which it is well known to be strongly dependent on heavy vehicles and more generally on engine noise at low speeds. Nevertheless, the propagation methodology has been improved in this new version, including diffraction also for low barriers. Since this issue is crucial in examining the frequency propagation, the method has been computed and compared with other ones. 2.1.3. Nord 2000 The Nord 2000 model (Jonasson et al., 2001) is the national standard for Nordic countries and it has a very detailed description of noise sources. Several vehicle categories are available, particularly for trucks that are divided into medium and heavy ones. Each category has different representative point sources that are located at different heights. Another interesting feature is having the full spectrum between 25 Hz and 10 kHz available for calculation. Sound power levels are derived from SPB measurements and they are coherent with previous validated models, so there is no need of weighting flows (cars can be considered in the first category and medium urban trucks in the second one that includes heavy vehicles with 2 axes). In addition to a detailed source model, the Nord 2000 also provides a propagation model based on geometrical ray theory combined with diffraction and analysis of Fresnel-zone effects. Significant refraction due to meteorological effects can also be taken into account. In order to compare the methods, a solution with standard meteorological condition according to guidelines (Kragh et al., 2006) is chosen; in the application of this method, different values of ground flow resistivity have been set to correspond to absorbing ground factors used (see Table 1). Being so detailed, the method is worthy to be applied and tested in this study to analyze in depth frequency content. 2.1.4. Local procedure The local procedure is based upon SPB measurements performed on an extra-urban road in Tuscany within the LEOPOLDO project: Sound Exposure Levels (SEL) are measured for different vehicles and speeds
according to the ISO 1996-2 (I. O. for Standardization, 2010). Thus, a fitted curve is available giving the value of SEL for each speed v: SEL ¼ Alog
v þ B: 50
ð1Þ
Then the sound power level per meter LW corresponding to the Leq per hour is calculated as follows: Q 0 LW ¼ SEL þ 10log þk 3600
ð2Þ
where Q is the number of vehicles per hour and k is a factor depending on the experimental distance and the road angle of sight (Ascari et al., 2010). Sound power is provided for each third octave band between 50 Hz and 10 kHz and it is given as an input of a linear source of the ISO 9613-2 method (I. O. for Standardization, 1996). The regression coefficients are established for each vehicle categories according to CNOSSOS-EU/HARMONOISE classification. Then, vehicle classes suitable for urban noise maps are selected: 1a (car) is considered as light vehicles and 2b and 2c (trucks with two axes) are considered as heavy vehicles, in accordance with the decision taken for the Nord 2000 model. 3. Results 3.1. Calibration in free field virtual scenario The calibration aimed to reach the same noise level through all the included methods at the measurement point (3 m height and 7.5 m far from the central line, R1). Results of the local procedure and standard methods are compared through software calculation. To verify the need of any calibration, methods are tested against the results of the NMPB96 model, which was already calibrated. In fact, a comparison between the interim method and measurements was carried out in 2008 to produce a weighted version validated on the noise map of Pisa (Ascari, 2009). This model needs a decreasing of the simulated traffic flow compared with the real one due to the lowering of the noise emission in the last decades. Basing on the actual simulation, also the new version of the French model turns out to overestimate. It needs a weighting factor but only for heavy vehicles (50% of real traffic is simulated): this is not anymore due to an obsolete database, but to the fact that city lorries are not as heavy as highway ones and this model makes no difference between lorries with 2 or 3 axes. On the other hand, the local procedure cannot be calibrated since it comes from measurements and it produces results that are consistent with the interim method. Finally, the Nord 2000 turns out to be enough comparable to the local procedure to need any reasonable calibration, even if it is a bit overestimating. After model weighting, A-levels on the reference points are quite well calibrated both at the measurement point and at greater distance (on NMPB reference curve 30 m far, 10 m height, R2). Results are reported in Table 2 for 100 light vehicles and 100 heavy vehicles (free field simulated scenario). Table 2 Noise A-levels at reference points according to the methods for light and heavy vehicles scenarios.
Table 1 Ground effect settings. Ground type
Absorbing factor
Flow resistivity [kN sm−4]
Water or concrete Mixed urban Fields
0 0.5 1
20,000 500 31.5
Model
Light @ R1
Light @ R2
Heavy @ R1
Heavy @ R2
Local Nord 2000 NMPB96 NMPB08 Mean Std.
57.5 59.2 56.2 56.5 57.4 1.4
50.4 51.6 49.7 50.1 50.5 0.8
64.2 64.9 62.6 63.0 63.7 1.1
57.0 57.5 56.1 56.5 56.8 0.6
E. Ascari et al. / Science of the Total Environment 505 (2015) 658–669 Table 3 Noise C-levels at reference points according to the methods for light and heavy vehicle scenarios. Model
Light @ R1
Light @ R2
Heavy @ R1
Heavy @ R2
Local Nord 2000 NMPB96 NMPB08 Mean Std.
62.2 65.5 61.3 61.3 62.6 2.0
55.4 58.6 55.0 55.0 56.0 1.7
72.4 72.5 67.8 67.8 70.1 2.7
65.9 65.8 61.5 61.4 63.7 2.5
These values, calculated in the software with different models, can be compared to the SEL value of a single light vehicle passing by at 50 km/h (parameter L1 according to ISO standard I. O. for Standardization, 1997) measured along several suburban roads in Tuscany. In fact, within the Leopoldo project in addition to new experimental surfaces, several standard surfaces were surveyed as a reference according to HARMONOISE procedure (Jonasson et al., 2004). The following equation highlights how to transform software data into SEL:
L1;sw ¼ LLight@R1 þ 10log
3600 →L1;sw ¼ LLight@R1 þ 15:6: Q
ð3Þ
The mean value for models turns out to be 72.9 ± 1.4 dBA in accordance with averaged measurements value of 73.4 ± 1.3 dBA. Obviously, this weighting methodology does not change the frequency content of models and they still differ a lot in terms of C weighted levels and spectra too (see Table 3 and Fig. 1). In Fig. 1 spectra are reported for all methods except for NMPB96 which is not set in the software to export spectra results. This calibration has outlined the differences between methods in the very simple free field virtual scenario; a validation through measurements is claimed.
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3.2. Validation in simple measurement sites Measurements have been carried out on two dual carriage roads (a motorway and an urban road) in Pisa in order to verify the averaged measured spectra where vehicle categories are mixed. Each real scenario has been simulated applying the detected traffic during the measurement-time (using the above corrected values for traffic flows based upon theoretical calibration and previous measurements). Two measurements have been performed, one along the motorway (embanked scenario, large distance, 90 km/h) at 4 m height and one along the urban road (flat scenario, next to the source, 60 km/h) at 3 m height. Spectra values and LA and LC levels are compared in Fig. 2 and in Table 4 (models cover different frequencies bands as already explained in the Methods section). The spectra analysis of both scenarios point out that generally Nord 2000 seems to be shaped like measurements better than the other methods despite reporting higher C and A weighted level differences. On the other hand, the French one is differently shaped, but it has the smaller differences in terms of C and A weighted levels. This is essentially due to a small overestimation of Local and Nord methodologies that reflects a net shift to higher values; instead, the French one, even not following the spectrum shape, produces good global values. The overestimation of the noise levels produced by Local and Nord methods could be related to screening effects of vehicle rows in dense traffic flows in the real scenario, which are not taken into account by the simulation and not necessarily by wrong sound power assigned. Moreover, correct shaped power spectra contribute to have reliable values behind barriers and obstacles, where frequency attenuations change the spectral content. Thus, good shaped methods are expected to obtain better results behind barriers. In the following paragraph, measurements will be shown in order to verify this hypothesis. 3.3. Comparison with in situ measurements with noise barriers Measurements shown in the previous paragraph for embanked and flat scenarios are carried out within campaigns of insertion
Fig. 1. Spectra at reference points R1 & R2 for light and heavy vehicles.
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a
b
Fig. 2. Measured vs. estimated spectra in embanked (a) and flat (b) scenarios.
loss monitoring. Therefore, they were performed next to noise barriers and other measurements behind barriers were acquired in the same places. So, it is possible to evaluate methods performances also behind barriers. At the embanked scenario the tested barrier is at 2.5 m height over the road plan and the flat one is at 4 m height; microphones are positioned respectively at 1.6 m and 1 m below the edges of barriers. Notice that in the flat scenario microphones are much closer to the roadside than in the embanked one. Fig. 3 shows spectra estimations and measurements. The Nord 2000 method seems to follow quite correctly the shape but there is a less effective dumping effect on the higher frequencies in the flat scenario. This may be due to the inaccuracy of the modeled distances, ground effects and maybe also the traffic screening effects which are expected to influence the high frequency dumping. Unfortunately, the local procedure seems to overestimate noise behind the barrier for the flat scenario: however, if we correct for the shift seen above in terms of high traffic flows, the overestimation decreases. French model, especially in terms of LC levels, seems to underestimate the noise behind the barrier. As expected, the better shaped methods provide better L C values behind barriers (see Table 5). As we can see from these real scenarios, not only the presence of obstacles but also their height, the distance from the road and maybe the terrain strongly affect results and their comparison with models. Besides all these effects, results highlight the difference between methods in modeling barriers and obstacles that should be better verified and understood. In this direction, JRC scenarios could help to focus only on barriers and obstacles in a complicated but controlled virtual scenario.
3.4. Different modelizations of specific aspects in virtual scenarios The city flat scenario has been implemented to verify the differences existing in propagation methods and to quantify effects of noise barriers according to methods. Traffic flows of 100 light vehicles and 100 heavy vehicles have been modeled in two separate scenarios. Three main zones are available in this scenario: unscreened area with single row buildings, screened area with single row buildings, and unscreened zone with multi-row buildings. The second zone is divided in two symmetric zones in which only adjoined zones differ. In fact, the first and each half of the second zones are not exactly symmetric because the first zone does not have segments of source at both sides as the second one (see Fig. 4). The identified tasks on the different zones are the following: 1. compare the first zone without barriers with the second one (A & B) with barriers and verify differences; 2. compare LFN effects at buildings in the third zone where complicated building scheme has been designed. In order to perform the first task, symmetric receivers with the numbering highlighted in Fig. 5 are compared. Differences according to methods between the first and the second zone (A and B sections) are calculated. Fig. 6 reports differences in terms of A and C levels for the JRC scenario with a traffic of 100 light vehicles at 50 km/h. It is evident that further receivers have a lower insertion loss according to Nord 2000 than with the other methods. This confirms that all the other methods use basically the same propagation and obstacle rules
Table 4 A & C level differences between models and measurements in flat and embanked scenarios. LA [dBA]
(a) emb. 4 m (b) flat 3 m
LC [dBC]
Meas. — Nord 2000
Meas. — NMPB08
Meas. — Local
Meas. — Nord 2000
Meas. — NMPB08
Meas. — local
−3.9 −2.1
1.2 1.3
−1.6 −1.6
−2.8 −2.3
−0.7 0.2
−1.3 −2.3
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a
b
Fig. 3. Measured vs. estimated spectra in screened embanked (a) and flat (b) scenarios.
(essentially based on ISO-9613); instead the Nord 2000 has its own very different methodology. Finally, if we calculate the difference between A and B sections within the second zone, we can notice that the Nord 2000 is completely different in considering other sections next to the examined one (Fig. 7). The Nord 2000 method depends more than the ISO-based ones on distance and obstacle specific orientation. This is confirmed performing task 2. In fact results in the third zone provide a quite constant value of L C − A except for the Nord 2000, which is the most varying along receivers (and the one with higher values). Finally we can notice that the local method is the only one that produces a great difference between light and heavy categories which is expected from common experience: Fig. 8(a) shows the LC − A values according to methods for light and heavy vehicle scenarios in the third zone (Fig. 8(b) highlights receivers positions). This virtual scenario has highlighted to what extent these models differ in considering obstacles and how much the estimated insertion loss, both in terms of C and A levels, differs according to methods. In particular, Nord 2000 has a completely different behavior which is worth to be further investigated in terms of options and settings before it could be said to correctly estimate low frequency contribution in general conditions.
3.5. Complex real scenarios (noise city maps) After having tested a complicated virtual scenario, the attempt is to verify differences in a real city center. The test was again performed in Pisa municipality where traffic model is available (Licitra and Memoli,
2008). As already said, different ground types have been used according to the land cover layer (see Table 1). The city center has a medieval layout with a lot of small roads crossed by main arteries. Therefore, a lot of low frequency noise is expected to affect people living also apparently far from high noise levels. Pisa, in fact, is a small city in Tuscany with less than 100,000 inhabitants; nevertheless, it has also important Universities with about 50,000 students, most of them living in the city. Therefore, since 2007 a pilot study implemented the 2002/49/EC Directive to test challenges of noise mapping (Licitra and Memoli, 2008). Noise studies did not stop and the city took part in a national project to attest the cardiovascular risks related with airport and road noise (SERA project 2012-2013 Ancona et al., 2013). The study succeeded in finding a correlation between noise levels and blood pressure permanent increases. However a deeper analysis of noise estimates can support the survey reliability and provide data to understand people perception and annoyance due to low frequency. In fact, self assessed annoyance has not been correlated within that study to noise and in particular to LFN. In this phase, simulation of the historical center of the city was completed (see Fig. 9), including more than 31,500 inhabitants and more than 55,000 students. Here a lot of surveys (on health and on pleasantness) have been already carried out. A previous study (CETUR, 1980) reported comparison between methods, in this paper a new simulation has been carried out in order to align all parameters as highlighted in already shown scenarios, also in terms of those factors that are usually left as default values but that differs between methods. In these simulations, also Powered two wheelers (PTW) are included because they have a relevant impact in the city. Since noise from PTW is known to be more
Table 5 A & C levels of differences between models and measurements in screened flat and embanked scenarios. LA [dBA]
(a) emb. 2 m (b) flat 3 m
LC [dBC]
Meas. — Nord 2000
Meas. — NMPB08
Meas. — local
Meas. — Nord 2000
Meas. — NMPB08
Meas. — local
0.1 −3.4
0.1 −1.0
1.1 −3.9
0.9 2.4
1.7 4.1
−1.1 −0.2
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Fig. 4. JRC city flat scenario: zone identification.
Fig. 5. First and second zone building scheme.
annoying (Voos, 2006), specific studies on their sound power were done in the past. Basing also upon findings in Greece (Paviotti and Vogiatzis, 2012), the flows of PTW were doubled and inserted as light vehicles in order to simulate their higher sound power.
Noise maps according to different acoustical methods have been calculated (local, NMPB08 and Nord 2000). The Lden values in terms of A-weighted and C-weighted levels are calculated to evaluate exposure, as the difference between themselves. The distribution of
Fig. 6. A & C level differences between the 1st and 2nd A zones and the 1st zone and 2nd B zones.
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Fig. 7. A & C level differences between 2nd A zone and 2nd B zone.
the differences between the local procedure and the standard methods both for A and C weighted levels has been evaluated. It can be observed in Table 6 that differences with Nord 2000 for A-weighted levels are
large; on the other hand, the French model is more similar to the local procedure. The differences in C-weighted level distributions have almost the same variance, but the differences with French model are
a
b
Fig. 8. a) LC − A levels in the 3rd zone according to methods for light and heavy vehicle scenarios; and the b) third zone building scheme.
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Fig. 9. Calculation area (pink) and limited traffic zone (blue). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
larger on average. Properties of distributions are summarized in Table 6 and in the box plot graph (Fig. 10). Analysis of LC − A was performed on the calculated grid (5 m grid step): results highlight high variability according to methods (see Fig. 11). It can be observed that NMPB 2008 values are quite constant, due to the fixed percentage of heavy vehicles in the road noise spectrum (all values below 8 dB). On the other hand, local procedure estimates a large amount (N60%) of calculation points over 8 dB and the Nord 2000 has about 100% of points over this threshold. The large variability of exposure according to models points out to be difficult in mapping this kind of indicator. The use of LC − A intended also to verify how much a mitigation measure as, for example, the restriction of vehicles access could change the low frequency content of the noise. In the previous paper (Ascari et al., 2013), an analysis with local procedure highlighted that inner areas, where a traffic limited zone is in force, were affected by higher values of this parameter. Here a confirmation is expected for the result obtained in Ascari et al. (2013) with local procedure, using the Nord 2000 model, even if absolute values of LC − A are so different. As shown in Fig. 12, lower values of LC − A are estimated right along the roads, higher values are located inside the city center, along the river, in the courtyards of the historical city center. To confirm these qualitative observations, comparative analysis of LC − A values inside and outside the traffic restricted area is carried out. Distribution of LC − A values of the calculated grid is reported in Fig. 13.
The figure shows that, even if average values are similar (14 and 15 dB), in the city center, where traffic policies have been applied, LC − A values have a different distribution. In particular, back façades and courtyards could have high–low frequency annoyance even if the traffic is low. Furthermore, it is possible to evaluate the increased perceived A level according to the formula described in Nilsson (2007) and Kephalopoulos et al. (2012): 0
LA ¼ LA þ 0:4LC−A :
ð4Þ
Using this indicator, a map reflecting both low frequency content and overall sound level is calculated.
Table 6 A &C levels of differences between models and measurements in screened flat and embanked scenarios. Local — NMPB08
Mean Std.
Local — Nord 2000
A — levels [dBA]
C — Levels [dBC]
A — levels [dBA]
C — levels [dBC]
0.34 1.32
4.21 2.90
2.96 2.79
−2.27 2.96
Fig. 10. Box plots of levels of differences (Lden) between methods in terms of dBA and dBC. Whiskers represent maximum and minimum values.
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Fig. 11. LC − A distribution in the city center according to the methods.
The here introduced indicator applies a correction that should be verified through specific local surveys. Nevertheless, it can be observed that in many areas of the city center the exposure rises significantly. In particular, if we consider only A-levels over 60 dBA as a threshold for annoyance, it is possible to estimate that more than 4500 inhabitants and about 4400 students increase their exposure of more than 3 dB according to this new indicator that takes into account the low frequency. In Fig. 14 dispersion of those building with a significant increase in exposure is reported. In particular, comparing the distributions with LA, it is clear that an average increase of 5–6 dB is perceived according to Nord 2000 (lower with local procedure). However, absolute increased perception is simply a demonstrative value because no local survey on perception has already been analyzed to this purpose. Whatever the amount of
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Fig. 13. LC − A distribution inside and outside the restricted area.
this increase would be, it is important to notice that it is not simply a translation of the distribution but it differs between inside and outside areas. In fact, in the inner areas the shape changes especially at low levels; on the other hand, outside, the middle levels are those which increase the most. 4. Conclusions Several simulations have been shown in order to highlight pro and cons of different prediction methods in evaluating low frequency noises. Current results point out that French methods, even being the reference models and accurate in terms of A-levels, are not appropriate to evaluate low frequency contribution with enough reliability. The new
Fig. 12. LC − A map according to the Nord 2000 method.
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Fig. 14. Distribution of buildings with a significantly higher exposure due to low frequency noise.
procedure, based upon local measurements and ISO 9613 propagation methodology, and the Nord 2000 methods have pointed out that low frequency perception could be higher in areas where action plans are in force. In particular, the rise of C levels and LC − A values both behind barriers and in limited traffic zones has been shown. Therefore, these considerations should be taken into account when establishing mitigation actions, paying attention to the low frequency modelizations and estimations. However, there is not a standard method that could be used without further analysis to provide a reliable low frequency exposure. On one hand the Nord 2000 seems to be accurate in reproducing noise emission spectra (as much as the local procedure) according to measurement database, on the other hand simulated values behind barriers seem to be too different from ones coming from other methods. In fact, the application of the Nord 2000 method with default values (especially in the case of virtual scenario) without measured data on ground impedance seems to produce results significantly different from all other methods. A deeper analysis, including new real scenarios specifically designed to assess noise behind barriers and obstacles, could permit to better compare results with measured input data. To have correct power spectra within official methods is paramount in order to use the LC − A indicator to compare different zones and correlate them with the reported annoyance of citizens. In fact, it has been shown that people exposure to LFN and inferable annoyance change significantly according to methods (percentage of calculation points being below 8 dB of LC − A could vary from 100% to 0%). Only the implementation of a robust method might lead to predict correctly annoyance after mitigation taking into account not only the overall energy pollution, but also the quality of noise perceived in terms of spectra and other sound quality criteria. In fact, preliminary data show a large amount of population affected by a significant increase of perceived levels due to a low frequency noise. Further studies will be carried out to assess relationship between LFN estimate and
reported annoyance in order to validate regression coefficient. In this studies psychoacoustical indicators will be also considered and compared to the estimate of LFN, in fact it is known that also loudness may be a relevant indicator of reported annoyance (Schomer et al., 2001). In evaluating annoyance correlation, a particular attention is due on the presence of other sources that could not be neglected at least in the case of Pisa city in which different studies on annoyance due to many sources have been already carried out (Licitra et al., 2011).
References Alimohammadi I, Sandrock S, Gohari M. The effects of low frequency noise on mental performance and annoyance. Environ Monit Assess 2013;185:7043–51. Ancona C, Ancona L, Badaloni C, Cesaroni G, Bucci S, Golini MN, et al. Impatto dell'inquinamento ambientale prodotto dagli aeroporti sulla salute dei residenti (progetto SERA — studio sugli effetti del rumore aeroportuale) (Airport impact on health (SERA project, study on airport noise effects)). Tech. rep., DEP Lazio; 2013. Ascari E. Traffic model uncertainty for noise mapping (Master's thesis) University of Pisa; 2009. Ascari E, Teti L, Cerchiai M, Licitra G. Low frequency modeling: analysis and comparison of standard national methods. Proceedings of 1st EAA-EUROREGIO, no. 023; 2010. Ascari E, Licitra G, Cerchiai M. Reliable methods for low frequency map to improve action plans. Proceedings of Internoise 2013; 2013. CETUR. Guide du bruit des transports terrestres: prevision des niveaux sonores. Cetur -Centre Etud Transp; 1980. Cetur, NMPB-Routes-96. Bruit des infrastructures routières, méthode de calcul incluant les effets météorologiques. CERTU, CSTB, LCPC, SETRA; 2000. Dutilleux G, Defrance J, Ecotière D, Gauvreau B, Berengier M, Besnard F, et al. NMPBRoutes-2008: the revision of the French method for road traffic noise prediction. Acta Acust united Ac 2010;96:452–62. I. O. for Standardization. ISO 9613-2 acoustics—attenuation of sound during propagation outdoors—part 2: general method of calculation; 1996. I. O. for Standardization. ISO 11819-1: acoustics — measurement of the influence of road surfaces on traffic noise — part 1: statistical pass-by method, revised and unchanged in 2013; 1997. I. O. for Standardization. ISO 1996-2:2010 acoustics — description, measurement and assessment of environmental noise — part 2: determination of environmental noise levels; 2010.
E. Ascari et al. / Science of the Total Environment 505 (2015) 658–669 Jonasson H. Test method for the whole vehicle. Tech. Rep. HAR11TR-020301–SP10, Harmonoise Project, Report; 2004. Jonasson H, Storeheier S. Nord 2000, new nordic prediction method for road traffic noise. Tech. Rep. SP Report 2001:10. SP Swedish National Testing and Research Institute; 2001. Jonasson H, Sandberg U, van Blokland G, Ejsmont J, Watts G, Luminari M. Source modelling of road vehicles — deliverable 9. Tech. Rep. HAR11TR-041210–SP10, Harmonoise Project, Report; 2004. Kaczmarska A, Luczak A. A study of annoyance caused by low frequency noise during mental work. Int J Occup Safety Ergon (JOSE) 2007;13/2:117–25. Kephalopoulos S, Paviotti M, Anfosso-Lédée F. Common Noise Assessment Methods in Europe (CNOSSOS-EU). Tech. Rep. EUR 25379 EN., Luxenbourg: Publication Office of the European Union; 2012. Kjellberg A, Tesarz M, Holmberg K, Landström U. Evaluation of frequency-weighted sound level measurements for prediction of low-frequency noise annoyance. Environ Int 1997;23:519–27. Kragh J, Jonasson H, Plovsing B, Sarinen A. User's guide Nord 2000 road, Tech. Rep. AV1171/06, Delta report; 2006. LEOPOLDO. Tuscany region. LEOPOLDO project. predisposizione delle linee guida per la progettazione ed il controllo delle pavimentazioni stradali per la viabilità ordinaria (Guidelines for planning and monitoring asphalts on ordinary roads). http://leopoldo.pjxp.com. Leventhall G, Pelmear P, Benton S. A review of published research on low frequency noise and its effects. Tech. Rep. Contract ref:EPG 1/2/50. DEFRA; 2003. Licitra G, Memoli G. Limits and advantages of good practice guide to noise mapping. J Acoust Soc Am 2008;123(5):3033. [06]. Licitra G, Cerchiai M, Ascari E, Teti L. Low frequency modelling: comparison between standard methods and a local procedure on standard testing scenarios. Proceedings of Forum Acusticum 2011; 2011. p. 689–94.
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Licitra G, Gallo P, Rossi E, Brambilla G. A novel method to determine multiexposure priority indices tested for Pisa action plan. Appl. Acoust. July 2011;72(8):505–10. Marsico G, Curcuruto S, Berlier F, Cerchiai M, Fabozzi T, Fogola J, et al. A comparison of noise simulation models. Proceedings of ICSV 17; 2010. Nilsson ME. A-weighted sound pressure level as an indicator of short-term loudness or annoyance of road-traffic sound. J Sound Vib 2007;302:197–207. Nilsson M, Berglund B. Noise annoyance and activity disturbance before and after the erection of a roadside noise barrier. J Acoust Soc Am 2006;119(4):2178–88. Nilsson M, Andéhn M, Leśna P. Evaluating roadside noise barriers using an annoyancereduction criterion. J Acoust Soc Am 2008;124(6):3561–7. Paviotti M, Kephalopoulos S. Implementation of directive 2002/49/ec on environmental noise: protocols for checking the equivalence of national noise mapping methods against the interim methods. Tech. rep., IHCP:JRC Technical report to DG ENV; 2008. Paviotti M, Vogiatzis K. On the outdoor annoyance from scooter and motorbike noise in the urban environment. Sci Total Environ 2012;430:223–30. Pawlaczyk-Luszczynska M, Dudarewicz A, Waszkowska M, Sliwinska-Kowalska M. Assessment of annoyance from low frequency and broadband noises. Int J Occup Med Environ Health 2003;16(4):337–43. Persson Waye K, Rylander R. The prevalence of annoyance and effects after long-term exposure to low-frequency noise. J Sound Vib 2001;240(3):483–97. Schomer PD, Suzuki Y, Saito F. Evaluation of loudness-level weightings for assessing the annoyance of environmental noise. J Acoust Soc Am 2001;110:2390–7. Schreurs E, Koeman T, Jabben J. Low frequency noise impact of road traffic in the Netherlands. Proceedings of Acoustics '08; 2008. p. 1943–8. Voos J. Noise annoyance caused by mopeds and other traffic sources. Proceedings of Internoise 2006; 2006. Yifan H, Guoqing D, Yiting Z, Youpeng H, Bangjun Z. Pair-wise comparison experiment on subjective annoyance rating of noise samples with different frequency spectrums but same A-weighted level. Appl Acoust 2008;69:1205–11.
Contents lists available at ScienceDirect
Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv
Low frequency noise impact from road traffic according to different noise prediction methods Elena Ascari a,b, Gaetano Licitra c,⁎, Luca Teti d, Mauro Cerchiai d a
CNR-IDASC, Via Fosso del Cavaliere 100, I-00133 Roma, Italy University of Siena, Via Roma 56, I-53100 Siena, Italy CNR-IPCF, Via Moruzzi 1, I-56124 Pisa, Italy d ARPAT — Settore Agenti Fisici-AVL, Via Vittorio Veneto 27, I-56127 Pisa, Italy b c
H I G H L I G H T S • • • • •
Low frequency noise (LFN) from road traffic is simulated with many mapping methods. The difference between C- and A-weighted levels is analyzed in several scenarios. Values are provided within virtual and real scenarios and for Pisa city center. LFN may increase in mitigated areas according to a new method and the Nord2000. Correct power spectra in methods are paramount in order to use the C–A indicator.
a r t i c l e
i n f o
Article history: Received 22 September 2014 Received in revised form 16 October 2014 Accepted 16 October 2014 Available online xxxx Editor: P. Kassomenos Keywords: Noise mapping Standard method comparison Low frequency Annoyance
a b s t r a c t The European Noise Directive 2002/49/EC requires to draw up noise action plans. Most of the implemented solutions consist in using barriers, even if some studies evidenced that annoyance could increase after their installation. This action dumps the high frequencies, decreasing the masking effect on low ones. Therefore, people annoyance and complaints may increase despite the mitigation. This can happen even in pedestrian zones near main roads due to the screening effect of first buildings row. In this paper, the authors analyze the post-operam screening effects in terms of low frequency noise. The difference between C- and A-weighted levels is calculated as annoyance indicator (LC − A). Different methods able to map noise with octave bands detail are tested in order to establish differences in the estimates of annoyance exposure. In particular, a comparison is carried out between data from interim method NMPB 96, its updated version 2008, NORD 2000 and those provided by a customized procedure through ISO 9613 propagation and Statistical Pass By measurements. Test sites are simulated in order to validate each model results through measurements. Results are discussed for real locations in Pisa city center and virtual scenarios in a rising scale of complexity. © 2014 Elsevier B.V. All rights reserved.
1. Introduction The need of a reliable noise prediction method has been pointed out after the two starting rounds of Noise Mapping according to the 2002/ 49/EC Directive. In addition to the difficulties in comparing results of different national methods, the inapplicability of interim method without calibration arises in local contexts. Thus, CNOSSOS-EU methodology has been set up by JRC (Kephalopoulos et al., 2012), on behalf of European Commission, to provide a common methodology. However, this methodology still lacks of implementation in commercial software and of application in legal terms due to the Member States resistance to change, though some software and validation tests were performed. ⁎ Corresponding author. E-mail address: [email protected] (G. Licitra).
http://dx.doi.org/10.1016/j.scitotenv.2014.10.052 0048-9697/© 2014 Elsevier B.V. All rights reserved.
Apart from the potential developments that may come in the future from the EU commission, this paper analyzes mapping methods using also the outcomes of the local LEOPOLDO project (LEOPOLDO). This project was cofounded by Tuscany Region (Italy) and started in 2005 to develop a detailed knowledge of traffic noise and to implement actions including low emission pavements. Its specific goal was to evaluate absorbent and low emission asphalts as a mitigation action by means of different measurement techniques and to assess the most reliable method. One of the most relevant side outcomes of this project is a large database of vehicle emission, measured according to the Statistical Pass By (SPB) methodology (I. O. for Standardization, 1997). This database not only will constitute the base to eventually verify CNOSSOS implementation in Tuscany, but also is suitable at the moment to evaluate accordance between available models and measured noise emission.
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The previous comparisons (Licitra et al., 2011; Ascari et al., 2010) have shown a significant difference between interim method and spectra measured with SPB techniques, especially in low frequency bands. Evaluating correctly the whole spectrum, especially the low frequency emission, is crucial because noise effects as annoyance or sleep disturbance increase with low frequency noise (LFN) predominance (Persson Waye and Rylander, 2001). Furthermore, LFN annoyance may arise at lower sound pressure levels than high frequency dominant noise (in rural areas not so far from highways, behind barriers, inside homes). This means that many mitigation measures, reducing noise energy, may not improve noise quality nor decrease annoyance (Nilsson et al., 2008). In literature, LFN generally indicates a broadband noise with sound energy dominating at 10–250 Hz (Pawlaczyk-Luszczynska et al., 2003; Leventhall et al., 2003): potential sources of LFN are ventilation system, pumps, compressors, diesel engines and transportation vehicles too. In particular, the importance of evaluating the impact of low frequency noise from road traffic is confirmed in several studies and the Dutch study (Schreurs et al., 2008) LC − A maps of the whole Dutch Highway network are presented. Road traffic is largely studied as low frequency source also by Nilsson et al. (Nilsson, 2007; Nilsson et al., 2008; Nilsson and Berglund, 2006). These studies not only underlined that LFN annoyance is reported in several contexts, but they also assert that it is more intensive than noises without dominant low frequency components (Persson Waye and Rylander, 2001). These studies reported how self-assessed annoyance increases also if a barrier is installed due to the turning up of low frequency noise predominance, since high frequencies are dumped by the barrier. The LC − A is the main indicator identified by Nilsson to relate the annoyance rate difference between barrier and non-barrier situations. It was previously used by different authors, particularly by Kjellberg et al. (1997) that also found a relation to correlate the annoyance perceived to this indicator. Furthermore, LFN has objective effects on humans such as permanent hearing threshold shift, behavior, sleep period, task performances and social attitude as monitored in several studies (Alimohammadi et al., 2013; Kaczmarska and Luczak, 2007). Moreover, the participants surveyed within these works reported some concentration problems and annoyance if exposed to low frequency noises during working activities. At the same time these studies also reported improved mental performances due to the increased arousal of participants. All these studies evidenced that LFN could be a source of stress. The importance of being able to predict low frequency is stated in the literature. Instead only few studies reported modeled values and to date there is not enough literature on low frequency mapping accuracy issues. This study identifies the most critical situations which are relevant to have a reliable method to estimate LFN. It also aims to assess in what extent noise maps are able to predict LFN exposure, comparing the outcomes of different methods and highlighting their pros & cons. In addition to the interim method (NMPB 1996), other standard methods available have been calculated as the NMPB 2008 and the Nord 2000. Furthermore, authors developed a simple tool to obtain emission spectra of roads according to LEOPOLDO database using a modelization with ISO9613 linear sources. This experimental method is tested and compared with official methods results. Tests are performed on virtual and real scenarios in a rising scale of complexity, ending with noise maps for Pisa city center (a Tuscany small city used as test case in previous studies). Results point out the LFN contribution according to the difference between C- and Aweighted levels (LC − A), which is considered to be suitable to evaluate annoyance due to a low frequency content also for road noise (Schreurs et al., 2008; Yifan et al., 2008). The aim of this paper is to evaluate the noise levels produced according to different methods in terms of LC − A. A complete LC − A map is reported for Pisa city center. Besides that, the final goal of the ongoing
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study is to provide a tool able to show a correlation between LC − A hot spots, specific position of the building in the urban fabric, annoyance reported and health effects. 2. Methods The comparison of different prediction methods is performed step by step, from simple to more elaborated and real contexts. At first, a comparison of the methods estimates in a free field condition is needed. In this context, A-weighted levels, C-weighted levels and spectra are evaluated for light and heavy vehicles according to all the tested methods. The calibration is carried out for two measurement positions: 1. the first is positioned as the microphone of the measurements campaign of the Statistical Pass By (7.5 m far from central line, 3 m height, according to HARMONOISE methodology Jonasson, 2004), hereafter named R1; 2. the second is positioned at the reference distance of the NMPB interim method (30 m far from central line, 10 m height), hereafter named R2. In order to verify the coherence of the methods to the measurements, a comparison with on site simple measurements is carried out. This test is performed both for measurements of direct noise and in screened situations (behind noise barriers) to verify the accordance of screening formulas provided by methods, i.e. the reliability of mapping models. Then, the differences in screened and more complex urban configurations are tested on ad hoc scenarios, established by JRC for method equivalence check (Paviotti and Kephalopoulos, 2008). Through those simulations, principal differences of methods in terms of LFN will be highlighted. Within JRC proposed scenarios, the city flat scenario has been chosen because it includes several configurations of buildings and barriers, providing enough complexity and, at the same time, having no altitude variations which are beyond the aims of this paper. Finally, noise maps for Pisa city center are analyzed in terms of LFN impact in specific areas. The similarities and differences between methods on these maps are going to underline the challenges of estimating LFN for road traffic. 2.1. Calculation methods All the simulations presented in this paper have been carried out with the software SoundPLAN 7.1. Differences could be found with other noise mapping software (Marsico et al., 2010). All calculations have been done at fixed temperature (10 °C) and humidity (70%), assuming no correction for favorable propagation. Only the first reflection has been taken into account and, if not specified further, a ground absorbing factor of 0.5 and building absorbing coefficient of 0.2 have been considered. The asphalt type depends on the applied method: we have generally chosen the type of asphalt within each method that does not apply correction to the source power level. This solution is in accordance with the local procedure that actually does not implement asphalt correction. Implemented methods with their settings are briefly described in the following. 2.1.1. NMPB 1996 The “Nouvelle Method de Prevision du Bruit” (NMPB 1996 Cetur, NMPB-Routes-96, 2000) is based upon Guide de Bruit (CETUR, 1980) database and it is the official interim method for the implementation of the 2002/49/EC (to be used by those countries which do not have their own standard). It has been chosen by EU commission because it has the advantage of taking into account both frequency propagation and tested meteorological corrections, requirements fulfilled by few other methods. However, the sound power level database is quite obsolete and weighted traffic flows have to be used in many applications to
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urban agglomerations. Moreover, another disadvantage is the use of a constant reference spectrum between 100 Hz and 5 kHz: no speed dependency is estimated and a fixed percentage of heavy vehicles is considered, regardless of the road type and real predominance of heavy vehicles. In fact, setting the amount of heavy vehicles only changes the overall sound power but not the spectrum. In this study, only A-levels and C-levels are reported in order to compare the official standard with other methods: unfortunately, the software does not include spectra export for this specific model. 2.1.2. NMPB 2008 The NMPB 2008 (Dutilleux et al., 2010) improved power level reliability with respect to its previous version, since the old database of the Guide de Bruit has been updated with new power levels. Therefore, light vehicles' flows do not need anymore adaptation in order to calibrate A-Levels. However, the heavy vehicles are still too noisy for urban environment (heavy traffic flows should be halved as shown in the following paragraphs) and it uses still a constant reference spectrum. As in the previous version, this characteristic makes French models generally unsuitable for the evaluation of the low frequency content, which it is well known to be strongly dependent on heavy vehicles and more generally on engine noise at low speeds. Nevertheless, the propagation methodology has been improved in this new version, including diffraction also for low barriers. Since this issue is crucial in examining the frequency propagation, the method has been computed and compared with other ones. 2.1.3. Nord 2000 The Nord 2000 model (Jonasson et al., 2001) is the national standard for Nordic countries and it has a very detailed description of noise sources. Several vehicle categories are available, particularly for trucks that are divided into medium and heavy ones. Each category has different representative point sources that are located at different heights. Another interesting feature is having the full spectrum between 25 Hz and 10 kHz available for calculation. Sound power levels are derived from SPB measurements and they are coherent with previous validated models, so there is no need of weighting flows (cars can be considered in the first category and medium urban trucks in the second one that includes heavy vehicles with 2 axes). In addition to a detailed source model, the Nord 2000 also provides a propagation model based on geometrical ray theory combined with diffraction and analysis of Fresnel-zone effects. Significant refraction due to meteorological effects can also be taken into account. In order to compare the methods, a solution with standard meteorological condition according to guidelines (Kragh et al., 2006) is chosen; in the application of this method, different values of ground flow resistivity have been set to correspond to absorbing ground factors used (see Table 1). Being so detailed, the method is worthy to be applied and tested in this study to analyze in depth frequency content. 2.1.4. Local procedure The local procedure is based upon SPB measurements performed on an extra-urban road in Tuscany within the LEOPOLDO project: Sound Exposure Levels (SEL) are measured for different vehicles and speeds
according to the ISO 1996-2 (I. O. for Standardization, 2010). Thus, a fitted curve is available giving the value of SEL for each speed v: SEL ¼ Alog
v þ B: 50
ð1Þ
Then the sound power level per meter LW corresponding to the Leq per hour is calculated as follows: Q 0 LW ¼ SEL þ 10log þk 3600
ð2Þ
where Q is the number of vehicles per hour and k is a factor depending on the experimental distance and the road angle of sight (Ascari et al., 2010). Sound power is provided for each third octave band between 50 Hz and 10 kHz and it is given as an input of a linear source of the ISO 9613-2 method (I. O. for Standardization, 1996). The regression coefficients are established for each vehicle categories according to CNOSSOS-EU/HARMONOISE classification. Then, vehicle classes suitable for urban noise maps are selected: 1a (car) is considered as light vehicles and 2b and 2c (trucks with two axes) are considered as heavy vehicles, in accordance with the decision taken for the Nord 2000 model. 3. Results 3.1. Calibration in free field virtual scenario The calibration aimed to reach the same noise level through all the included methods at the measurement point (3 m height and 7.5 m far from the central line, R1). Results of the local procedure and standard methods are compared through software calculation. To verify the need of any calibration, methods are tested against the results of the NMPB96 model, which was already calibrated. In fact, a comparison between the interim method and measurements was carried out in 2008 to produce a weighted version validated on the noise map of Pisa (Ascari, 2009). This model needs a decreasing of the simulated traffic flow compared with the real one due to the lowering of the noise emission in the last decades. Basing on the actual simulation, also the new version of the French model turns out to overestimate. It needs a weighting factor but only for heavy vehicles (50% of real traffic is simulated): this is not anymore due to an obsolete database, but to the fact that city lorries are not as heavy as highway ones and this model makes no difference between lorries with 2 or 3 axes. On the other hand, the local procedure cannot be calibrated since it comes from measurements and it produces results that are consistent with the interim method. Finally, the Nord 2000 turns out to be enough comparable to the local procedure to need any reasonable calibration, even if it is a bit overestimating. After model weighting, A-levels on the reference points are quite well calibrated both at the measurement point and at greater distance (on NMPB reference curve 30 m far, 10 m height, R2). Results are reported in Table 2 for 100 light vehicles and 100 heavy vehicles (free field simulated scenario). Table 2 Noise A-levels at reference points according to the methods for light and heavy vehicles scenarios.
Table 1 Ground effect settings. Ground type
Absorbing factor
Flow resistivity [kN sm−4]
Water or concrete Mixed urban Fields
0 0.5 1
20,000 500 31.5
Model
Light @ R1
Light @ R2
Heavy @ R1
Heavy @ R2
Local Nord 2000 NMPB96 NMPB08 Mean Std.
57.5 59.2 56.2 56.5 57.4 1.4
50.4 51.6 49.7 50.1 50.5 0.8
64.2 64.9 62.6 63.0 63.7 1.1
57.0 57.5 56.1 56.5 56.8 0.6
E. Ascari et al. / Science of the Total Environment 505 (2015) 658–669 Table 3 Noise C-levels at reference points according to the methods for light and heavy vehicle scenarios. Model
Light @ R1
Light @ R2
Heavy @ R1
Heavy @ R2
Local Nord 2000 NMPB96 NMPB08 Mean Std.
62.2 65.5 61.3 61.3 62.6 2.0
55.4 58.6 55.0 55.0 56.0 1.7
72.4 72.5 67.8 67.8 70.1 2.7
65.9 65.8 61.5 61.4 63.7 2.5
These values, calculated in the software with different models, can be compared to the SEL value of a single light vehicle passing by at 50 km/h (parameter L1 according to ISO standard I. O. for Standardization, 1997) measured along several suburban roads in Tuscany. In fact, within the Leopoldo project in addition to new experimental surfaces, several standard surfaces were surveyed as a reference according to HARMONOISE procedure (Jonasson et al., 2004). The following equation highlights how to transform software data into SEL:
L1;sw ¼ LLight@R1 þ 10log
3600 →L1;sw ¼ LLight@R1 þ 15:6: Q
ð3Þ
The mean value for models turns out to be 72.9 ± 1.4 dBA in accordance with averaged measurements value of 73.4 ± 1.3 dBA. Obviously, this weighting methodology does not change the frequency content of models and they still differ a lot in terms of C weighted levels and spectra too (see Table 3 and Fig. 1). In Fig. 1 spectra are reported for all methods except for NMPB96 which is not set in the software to export spectra results. This calibration has outlined the differences between methods in the very simple free field virtual scenario; a validation through measurements is claimed.
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3.2. Validation in simple measurement sites Measurements have been carried out on two dual carriage roads (a motorway and an urban road) in Pisa in order to verify the averaged measured spectra where vehicle categories are mixed. Each real scenario has been simulated applying the detected traffic during the measurement-time (using the above corrected values for traffic flows based upon theoretical calibration and previous measurements). Two measurements have been performed, one along the motorway (embanked scenario, large distance, 90 km/h) at 4 m height and one along the urban road (flat scenario, next to the source, 60 km/h) at 3 m height. Spectra values and LA and LC levels are compared in Fig. 2 and in Table 4 (models cover different frequencies bands as already explained in the Methods section). The spectra analysis of both scenarios point out that generally Nord 2000 seems to be shaped like measurements better than the other methods despite reporting higher C and A weighted level differences. On the other hand, the French one is differently shaped, but it has the smaller differences in terms of C and A weighted levels. This is essentially due to a small overestimation of Local and Nord methodologies that reflects a net shift to higher values; instead, the French one, even not following the spectrum shape, produces good global values. The overestimation of the noise levels produced by Local and Nord methods could be related to screening effects of vehicle rows in dense traffic flows in the real scenario, which are not taken into account by the simulation and not necessarily by wrong sound power assigned. Moreover, correct shaped power spectra contribute to have reliable values behind barriers and obstacles, where frequency attenuations change the spectral content. Thus, good shaped methods are expected to obtain better results behind barriers. In the following paragraph, measurements will be shown in order to verify this hypothesis. 3.3. Comparison with in situ measurements with noise barriers Measurements shown in the previous paragraph for embanked and flat scenarios are carried out within campaigns of insertion
Fig. 1. Spectra at reference points R1 & R2 for light and heavy vehicles.
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a
b
Fig. 2. Measured vs. estimated spectra in embanked (a) and flat (b) scenarios.
loss monitoring. Therefore, they were performed next to noise barriers and other measurements behind barriers were acquired in the same places. So, it is possible to evaluate methods performances also behind barriers. At the embanked scenario the tested barrier is at 2.5 m height over the road plan and the flat one is at 4 m height; microphones are positioned respectively at 1.6 m and 1 m below the edges of barriers. Notice that in the flat scenario microphones are much closer to the roadside than in the embanked one. Fig. 3 shows spectra estimations and measurements. The Nord 2000 method seems to follow quite correctly the shape but there is a less effective dumping effect on the higher frequencies in the flat scenario. This may be due to the inaccuracy of the modeled distances, ground effects and maybe also the traffic screening effects which are expected to influence the high frequency dumping. Unfortunately, the local procedure seems to overestimate noise behind the barrier for the flat scenario: however, if we correct for the shift seen above in terms of high traffic flows, the overestimation decreases. French model, especially in terms of LC levels, seems to underestimate the noise behind the barrier. As expected, the better shaped methods provide better L C values behind barriers (see Table 5). As we can see from these real scenarios, not only the presence of obstacles but also their height, the distance from the road and maybe the terrain strongly affect results and their comparison with models. Besides all these effects, results highlight the difference between methods in modeling barriers and obstacles that should be better verified and understood. In this direction, JRC scenarios could help to focus only on barriers and obstacles in a complicated but controlled virtual scenario.
3.4. Different modelizations of specific aspects in virtual scenarios The city flat scenario has been implemented to verify the differences existing in propagation methods and to quantify effects of noise barriers according to methods. Traffic flows of 100 light vehicles and 100 heavy vehicles have been modeled in two separate scenarios. Three main zones are available in this scenario: unscreened area with single row buildings, screened area with single row buildings, and unscreened zone with multi-row buildings. The second zone is divided in two symmetric zones in which only adjoined zones differ. In fact, the first and each half of the second zones are not exactly symmetric because the first zone does not have segments of source at both sides as the second one (see Fig. 4). The identified tasks on the different zones are the following: 1. compare the first zone without barriers with the second one (A & B) with barriers and verify differences; 2. compare LFN effects at buildings in the third zone where complicated building scheme has been designed. In order to perform the first task, symmetric receivers with the numbering highlighted in Fig. 5 are compared. Differences according to methods between the first and the second zone (A and B sections) are calculated. Fig. 6 reports differences in terms of A and C levels for the JRC scenario with a traffic of 100 light vehicles at 50 km/h. It is evident that further receivers have a lower insertion loss according to Nord 2000 than with the other methods. This confirms that all the other methods use basically the same propagation and obstacle rules
Table 4 A & C level differences between models and measurements in flat and embanked scenarios. LA [dBA]
(a) emb. 4 m (b) flat 3 m
LC [dBC]
Meas. — Nord 2000
Meas. — NMPB08
Meas. — Local
Meas. — Nord 2000
Meas. — NMPB08
Meas. — local
−3.9 −2.1
1.2 1.3
−1.6 −1.6
−2.8 −2.3
−0.7 0.2
−1.3 −2.3
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a
b
Fig. 3. Measured vs. estimated spectra in screened embanked (a) and flat (b) scenarios.
(essentially based on ISO-9613); instead the Nord 2000 has its own very different methodology. Finally, if we calculate the difference between A and B sections within the second zone, we can notice that the Nord 2000 is completely different in considering other sections next to the examined one (Fig. 7). The Nord 2000 method depends more than the ISO-based ones on distance and obstacle specific orientation. This is confirmed performing task 2. In fact results in the third zone provide a quite constant value of L C − A except for the Nord 2000, which is the most varying along receivers (and the one with higher values). Finally we can notice that the local method is the only one that produces a great difference between light and heavy categories which is expected from common experience: Fig. 8(a) shows the LC − A values according to methods for light and heavy vehicle scenarios in the third zone (Fig. 8(b) highlights receivers positions). This virtual scenario has highlighted to what extent these models differ in considering obstacles and how much the estimated insertion loss, both in terms of C and A levels, differs according to methods. In particular, Nord 2000 has a completely different behavior which is worth to be further investigated in terms of options and settings before it could be said to correctly estimate low frequency contribution in general conditions.
3.5. Complex real scenarios (noise city maps) After having tested a complicated virtual scenario, the attempt is to verify differences in a real city center. The test was again performed in Pisa municipality where traffic model is available (Licitra and Memoli,
2008). As already said, different ground types have been used according to the land cover layer (see Table 1). The city center has a medieval layout with a lot of small roads crossed by main arteries. Therefore, a lot of low frequency noise is expected to affect people living also apparently far from high noise levels. Pisa, in fact, is a small city in Tuscany with less than 100,000 inhabitants; nevertheless, it has also important Universities with about 50,000 students, most of them living in the city. Therefore, since 2007 a pilot study implemented the 2002/49/EC Directive to test challenges of noise mapping (Licitra and Memoli, 2008). Noise studies did not stop and the city took part in a national project to attest the cardiovascular risks related with airport and road noise (SERA project 2012-2013 Ancona et al., 2013). The study succeeded in finding a correlation between noise levels and blood pressure permanent increases. However a deeper analysis of noise estimates can support the survey reliability and provide data to understand people perception and annoyance due to low frequency. In fact, self assessed annoyance has not been correlated within that study to noise and in particular to LFN. In this phase, simulation of the historical center of the city was completed (see Fig. 9), including more than 31,500 inhabitants and more than 55,000 students. Here a lot of surveys (on health and on pleasantness) have been already carried out. A previous study (CETUR, 1980) reported comparison between methods, in this paper a new simulation has been carried out in order to align all parameters as highlighted in already shown scenarios, also in terms of those factors that are usually left as default values but that differs between methods. In these simulations, also Powered two wheelers (PTW) are included because they have a relevant impact in the city. Since noise from PTW is known to be more
Table 5 A & C levels of differences between models and measurements in screened flat and embanked scenarios. LA [dBA]
(a) emb. 2 m (b) flat 3 m
LC [dBC]
Meas. — Nord 2000
Meas. — NMPB08
Meas. — local
Meas. — Nord 2000
Meas. — NMPB08
Meas. — local
0.1 −3.4
0.1 −1.0
1.1 −3.9
0.9 2.4
1.7 4.1
−1.1 −0.2
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Fig. 4. JRC city flat scenario: zone identification.
Fig. 5. First and second zone building scheme.
annoying (Voos, 2006), specific studies on their sound power were done in the past. Basing also upon findings in Greece (Paviotti and Vogiatzis, 2012), the flows of PTW were doubled and inserted as light vehicles in order to simulate their higher sound power.
Noise maps according to different acoustical methods have been calculated (local, NMPB08 and Nord 2000). The Lden values in terms of A-weighted and C-weighted levels are calculated to evaluate exposure, as the difference between themselves. The distribution of
Fig. 6. A & C level differences between the 1st and 2nd A zones and the 1st zone and 2nd B zones.
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Fig. 7. A & C level differences between 2nd A zone and 2nd B zone.
the differences between the local procedure and the standard methods both for A and C weighted levels has been evaluated. It can be observed in Table 6 that differences with Nord 2000 for A-weighted levels are
large; on the other hand, the French model is more similar to the local procedure. The differences in C-weighted level distributions have almost the same variance, but the differences with French model are
a
b
Fig. 8. a) LC − A levels in the 3rd zone according to methods for light and heavy vehicle scenarios; and the b) third zone building scheme.
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Fig. 9. Calculation area (pink) and limited traffic zone (blue). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
larger on average. Properties of distributions are summarized in Table 6 and in the box plot graph (Fig. 10). Analysis of LC − A was performed on the calculated grid (5 m grid step): results highlight high variability according to methods (see Fig. 11). It can be observed that NMPB 2008 values are quite constant, due to the fixed percentage of heavy vehicles in the road noise spectrum (all values below 8 dB). On the other hand, local procedure estimates a large amount (N60%) of calculation points over 8 dB and the Nord 2000 has about 100% of points over this threshold. The large variability of exposure according to models points out to be difficult in mapping this kind of indicator. The use of LC − A intended also to verify how much a mitigation measure as, for example, the restriction of vehicles access could change the low frequency content of the noise. In the previous paper (Ascari et al., 2013), an analysis with local procedure highlighted that inner areas, where a traffic limited zone is in force, were affected by higher values of this parameter. Here a confirmation is expected for the result obtained in Ascari et al. (2013) with local procedure, using the Nord 2000 model, even if absolute values of LC − A are so different. As shown in Fig. 12, lower values of LC − A are estimated right along the roads, higher values are located inside the city center, along the river, in the courtyards of the historical city center. To confirm these qualitative observations, comparative analysis of LC − A values inside and outside the traffic restricted area is carried out. Distribution of LC − A values of the calculated grid is reported in Fig. 13.
The figure shows that, even if average values are similar (14 and 15 dB), in the city center, where traffic policies have been applied, LC − A values have a different distribution. In particular, back façades and courtyards could have high–low frequency annoyance even if the traffic is low. Furthermore, it is possible to evaluate the increased perceived A level according to the formula described in Nilsson (2007) and Kephalopoulos et al. (2012): 0
LA ¼ LA þ 0:4LC−A :
ð4Þ
Using this indicator, a map reflecting both low frequency content and overall sound level is calculated.
Table 6 A &C levels of differences between models and measurements in screened flat and embanked scenarios. Local — NMPB08
Mean Std.
Local — Nord 2000
A — levels [dBA]
C — Levels [dBC]
A — levels [dBA]
C — levels [dBC]
0.34 1.32
4.21 2.90
2.96 2.79
−2.27 2.96
Fig. 10. Box plots of levels of differences (Lden) between methods in terms of dBA and dBC. Whiskers represent maximum and minimum values.
E. Ascari et al. / Science of the Total Environment 505 (2015) 658–669
Fig. 11. LC − A distribution in the city center according to the methods.
The here introduced indicator applies a correction that should be verified through specific local surveys. Nevertheless, it can be observed that in many areas of the city center the exposure rises significantly. In particular, if we consider only A-levels over 60 dBA as a threshold for annoyance, it is possible to estimate that more than 4500 inhabitants and about 4400 students increase their exposure of more than 3 dB according to this new indicator that takes into account the low frequency. In Fig. 14 dispersion of those building with a significant increase in exposure is reported. In particular, comparing the distributions with LA, it is clear that an average increase of 5–6 dB is perceived according to Nord 2000 (lower with local procedure). However, absolute increased perception is simply a demonstrative value because no local survey on perception has already been analyzed to this purpose. Whatever the amount of
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Fig. 13. LC − A distribution inside and outside the restricted area.
this increase would be, it is important to notice that it is not simply a translation of the distribution but it differs between inside and outside areas. In fact, in the inner areas the shape changes especially at low levels; on the other hand, outside, the middle levels are those which increase the most. 4. Conclusions Several simulations have been shown in order to highlight pro and cons of different prediction methods in evaluating low frequency noises. Current results point out that French methods, even being the reference models and accurate in terms of A-levels, are not appropriate to evaluate low frequency contribution with enough reliability. The new
Fig. 12. LC − A map according to the Nord 2000 method.
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Fig. 14. Distribution of buildings with a significantly higher exposure due to low frequency noise.
procedure, based upon local measurements and ISO 9613 propagation methodology, and the Nord 2000 methods have pointed out that low frequency perception could be higher in areas where action plans are in force. In particular, the rise of C levels and LC − A values both behind barriers and in limited traffic zones has been shown. Therefore, these considerations should be taken into account when establishing mitigation actions, paying attention to the low frequency modelizations and estimations. However, there is not a standard method that could be used without further analysis to provide a reliable low frequency exposure. On one hand the Nord 2000 seems to be accurate in reproducing noise emission spectra (as much as the local procedure) according to measurement database, on the other hand simulated values behind barriers seem to be too different from ones coming from other methods. In fact, the application of the Nord 2000 method with default values (especially in the case of virtual scenario) without measured data on ground impedance seems to produce results significantly different from all other methods. A deeper analysis, including new real scenarios specifically designed to assess noise behind barriers and obstacles, could permit to better compare results with measured input data. To have correct power spectra within official methods is paramount in order to use the LC − A indicator to compare different zones and correlate them with the reported annoyance of citizens. In fact, it has been shown that people exposure to LFN and inferable annoyance change significantly according to methods (percentage of calculation points being below 8 dB of LC − A could vary from 100% to 0%). Only the implementation of a robust method might lead to predict correctly annoyance after mitigation taking into account not only the overall energy pollution, but also the quality of noise perceived in terms of spectra and other sound quality criteria. In fact, preliminary data show a large amount of population affected by a significant increase of perceived levels due to a low frequency noise. Further studies will be carried out to assess relationship between LFN estimate and
reported annoyance in order to validate regression coefficient. In this studies psychoacoustical indicators will be also considered and compared to the estimate of LFN, in fact it is known that also loudness may be a relevant indicator of reported annoyance (Schomer et al., 2001). In evaluating annoyance correlation, a particular attention is due on the presence of other sources that could not be neglected at least in the case of Pisa city in which different studies on annoyance due to many sources have been already carried out (Licitra et al., 2011).
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