FINAL REPORT. On Project Supplemental Guidance on the Application of FHWA s Traffic Noise Model (TNM) APPENDIX L Tunnel Openings

Transcription

1 FINAL REPORT On Project 2-34 Supplemental Guidance on the Application of FHWA s Traffic Noise Model (TNM) APPENDIX L Tunnel Openings Prepared for: National Cooperative Highway Research Program (NCHRP) Transportation Research Board of The National Academies March 14 HMMH Report No. 47 Prepared by: Research Topic Lead in association with Bowlby & Associates, Inc. Environmental Acoustics Grant S. Anderson Douglas E. Barrett

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3 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM Contents... L-1 L.1 Introduction... L-1 L.2 Modeling Techniques and Validation Data Compiled... L-1 L.2.1 Woehner, Noise Control Engineering Journal L-1 L.2.2 Olafsen, Inter-noise L-2 L.2.3 Takagi, Inter-noise... L-2 L.2.4 Tachibana, Inter-noise L-3 L.2. Yano, Inter-noise 7... L-3 L.2.6 Probst, Noise Control Engineering Journal, 1... L-4 L.3 Gaps or Weaknesses Identified... L-6 L.4 Evaluation of Candidate Modeling Techniques... L-6 L.4.1 Overview... L-7 L.4.2 Perpendicular road across & just outside tunnel opening with a single road inside the tunnel. L-8 L.4.3 Perpendicular road across & just inside tunnel opening with a single road inside the tunnel... L-9 L.4.4 Three parallel and evenly spaced roads inside the tunnel each with 1X volume of road outside..... L-1 L.4. Three parallel and evenly spaced roads inside the tunnel each with 2.X volume of road outside... L-11 L.4.6 Four parallel and evenly spaced roads inside the tunnel each with 1.9X volume of road outside.... L-11 L.4.7 Statistics of the differences between TNM-calculated noise levels and SoundPLAN-calculated noise levels... L-11 L. Tunnel Effects... L-11 L.6 Traffic Noise Measurements near a Tunnel Opening... L-12 iii

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5 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM Appendix L L.1 Introduction Tunnel Openings In addition to traffic volumes and speeds, the non-traffic factors that affect the noise levels radiated from tunnel openings include scattering and absorption elements inside tunnels and the size of the tunnel. Most highway tunnels have acoustically hard surfaces with limited absorption, and they often have few scattering elements besides the vehicles themselves. Therefore, noise levels at tunnel openings are often somewhat greater than they would be otherwise without the presence of the tunnel. We conducted a data survey and literature review to determine if existing noise measurement data exist that are sufficient for model validation. No data were forthcoming from the survey, and limited measurement data are cited in the published literature. Past modeling approaches have included the placement of point sources, area sources or short roadways across the mouth of tunnels, with the sound power of the point or area sources or volumes of traffic on the roadways adjusted to represent the appropriate level of noise emanating from the tunnel opening. These approaches have the advantage of putting sources very close to the proper location and allowing for any degree of sound energy to be attributed to the tunnel opening emissions. A significant uncertainty in modeling lies in determining an appropriate sound power level (or traffic volumes on roadways) to reasonably represent the tunnel opening emissions. The literature points out that the degree of absorption and scattering present inside the tunnel, particularly near the opening is an important parameter. Another uncertainty in modeling relates to the directional characteristics of the sound emanating from the opening. Best practices presented include relatively precise methods for more detailed analyses, and more approximate approaches, such as for environmental document studies, where such detail and precision is not necessary. L.2 Modeling Techniques and Validation Data Compiled The only modeling techniques with validation data that were available were from the published literature. The data survey produced no usable information. Below we summarize the papers that present practical approaches for modeling and/or validation data that may be of value. L.2.1 Woehner, Noise Control Engineering Journal 1992 Helmut Woehner s paper describes and presents the results of measurements in and around some tunnels in Germany. 1 At one relatively short tunnel, sound level measurements were conducted at several locations inside, at the opening, and adjacent to the same highway away from the opening both before and after absorptive treatment was applied to the interior of the tunnel with a hard, reflective surface. Relative to the levels adjacent to the highway away from the tunnel with reflective surface, levels at the opening were found to be 6 to 9 dba higher, and inside the tunnel, 1 to 14 dba higher. A diffuse sound field was observed at the opening of the reflective tunnel, with constant levels over the area of the opening. The same tunnel after absorptive linings were installed showed increases of up to only 3 to 4 dba at the portal. A mathematical model to assess the value of absorption is discussed, but no details are presented. Since no clear details of the measurement locations are given, the results of this paper cannot effectively be used 1 Woehner, Helmut, Sound Propagation at Tunnel Openings, Noise Control Engineering Journal, Vol. 39(2), pp. 47-6, L-1

6 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM for validation, but the general conclusions can be considered and compared during the model comparisons and validation process. Of particular interest and potential value is the application of absorptive material to an existing tunnel, and the quantitative results presented. L.2.2 Olafsen, Inter-noise 1996 The Olafsen paper 2 describes a mathematical model where the tunnel is assumed to be a circular tube where the sound power generated inside the tunnel is equal to the sound power radiated at the openings times a reduction factor. The reduction factor is based on a decay function integrated over the length of the tunnel, which is evaluated as a function of frequency, since the tunnel absorption is frequency dependent. Measurements of the time histories of individual vehicles traveling in two Norwegian highway tunnels allowed for the development of the tunnel absorption factors by octave band for each tunnel. The paper suggests that the sound power radiated by the tunnel openings can be modeled as an area source or as a point source, and that the point source approach is sufficient for most practical purposes. A test of the tunnel opening noise prediction model is presented, with a prediction compared with a single measurement of L eq at one nearby location. The computed level is within one dba of measured, but of course, it is one data point. The author states that validation of tunnel opening models is confounded by the traffic noise from the open road adjacent to the opening. The author further states that the model presented has been in use for several years to predict noise from road tunnel openings. L.2.3 Takagi, Inter-noise Takagi, et. al. 3 develop a model of tunnel noise opening emissions for tunnels of both semi-circular and rectangular cross-section. As in the Olafsen study, the Takagi model derives sound power at the mouth of the tunnel from assumed sound power from vehicular traffic inside the tunnel, integrated along the length of the tunnel with an assumed absorption factor. Tunnels of both semi-circular and rectangular cross-section and with concrete surfaces were modeled using geometrical acoustics propagation concepts and then compared with measurements. It appears that the study was conducted to support the development of a tunnel opening component of the ASJ (Acoustical Society of Japan) Model 1998, a comprehensive road noise model. 4 Modeling results were compared with measurements at 1 locations outside the tunnel of the time-history of a single vehicle traveling in the tunnel, and also of the noise from continuous traffic. Absorption parameters for broadband A-weighted traffic noise of.3,.4 and.7 were tested in the model, which was used to develop time-history plots of the A-level of the single vehicle sound level at the mouth of the tunnel. These plots were compared with the measured sound levels, and the absorption parameter of.4 was found to provide the best agreement. The paper later develops a relationship between the absorption parameter and sound absorption coefficient applicable to the overall A-weighted sound level. The paper briefly presents validation results for L Aeq at the 1 measurement points near the tunnel opening. The paper cites the methodology of the ASJ Model 1998 as being used to compute the L Aeq values at the tunnel entrance, and presents the validation data and curve fit results in the graph below. 2 Olafsen, S., Noise from road tunnel openings an engineering approach, proceedings of Inter-noise 96, pp Takagi, K., T. Miyake, K. Yamamoto, H. Tachibana, Prediction of road traffic noise around tunnel mouth, proceedings of Inter-noise, paper no Research Committee of Traffic Noise in Acoustical Society of Japan, ASJ prediction model 1998 for road traffic noise, J. Acoust. Soc. Jpn, Vol. (4), pp , L-2

7 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM The paper is not clear as to whether these values and comparisons are based on single-vehicle passages or continuous traffic streams. The average difference between measured and computed L Aeq is said to be 1.6 db. The ASJ Model 1998 has not yet been investigated for its potential as a modeling tool for this Task Area, but it has potential as a way to develop estimates of tunnel opening noise levels and possible use as a validation tool for TNM modeling approaches. Takagi - ASJ Model 1998 tunnel opening validation comparison L.2.4 Tachibana, Inter-noise 1999 Copyright SFA - Internoise Hideki Tachibana and colleagues report on a scale model study of the sound radiation from a tunnel opening. This study was conducted in support of the development of the tunnel opening model in ASJ Model 1998, mentioned in the previous section. A scale model of a tunnel was constructed and tested with and without various degrees and types of absorptive treatments. An electric spark discharge was used as the sound source. The study appears to have been conducted well, and concludes that absorptive treatments are highly effective in a tunnel, and treatments near only the opening can be effective for reducing noise radiated out of the tunnel opening. No measurements of full scale tunnels were conducted. The Takagi geometrical model is cited. L.2. Yano, Inter-noise 7 Hiroo Yanoo and colleagues report on a study of the effects adding absorptive material to a full-scale tunnel near a residential area. 6 The tunnel had been built to abate noise from waste trucks accessing a treatment facility near a residential area, so significant noise radiation from the tunnel openings was unacceptable. Measurements using a loudspeaker in the tunnel and swept-sine signals enabled the researchers to determine the effectiveness of sound absorptive boards applied to the inside of the otherwise hard Tachibana, H., S. Sakamoto, A. Nakai, Scale model experiment on sound radiation from tunnel mouth, proceedings of Inter-noise Yano, H., S. Yokoyama, H. Tachibana, M. Owaki, The effect of reducing noise radiation from a tunnel mouth by sound absorption treatment, proceedings of Inter-noise 7, Istanbul, Turkey, pp L-3

8 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM concrete tunnel. Reductions of db to 1 db in the Hz to Hz octave bands were observed at the tunnel opening. No measurements of truck noise levels before and after treatment were conducted. L.2.6 Probst, Noise Control Engineering Journal, 1 In his recent paper, Wolfgang Probst cites some of the studies described above, as well as some in German that we have not reviewed for this report. 7 In his comprehensive and detailed article, Mr. Probst outlines a well thought-out approach for modeling tunnel opening noise emissions using national noise emission models as a starting point (including the FHWA TNM). The modeling method is based on wellestablished ray-tracing modeling methods. (The author is with Datakustik, the developers of CadnaA, and his modeling tools and approach appear to be based on an advanced application of CadnaA.) In the article he provides tables and curves of adjustments to account for varying tunnel cross section and length, and absorption characteristics, including location and length. Interestingly, the author shows how tunnels can be modeled using standard room acoustics models, and he offers the figure below, suggesting the two cases shown are equivalent. And, the acoustical model for Probst modeling of tunnels using room acoustics models Institute of Noise Control Engineering tunnels is developed using well-understood room acoustics methods and software (CadnaR). The result is sound power level in the artificial room, which relates to the sound power level at the tunnel opening. The model presented has the capability to model uneven distribution of absorptive material in the tunnel/room. The author s analysis also develops directivity for the tunnel opening. This is developed based on standard ray-tracing modeling methods. The figure below from the paper shows the computed directivity in the horizontal plane from a tunnel of rectangular section and size 1m x 6 m. This directivity characteristic results in levels from the tunnel opening ranging by about 1 db over the degree angle from on-axis with the tunnel to perpendicular to the road at the opening. 7 Probst, Wolfgang, Prediction of sound radiated from tunnel openings, Noise Control Engineering Journal, Vol. 8(2), pp , 1. L-4

9 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM Probst computed directivity of a tunnel opening in the horizontal plane Institute of Noise Control Engineering The author suggests modeling the tunnel opening as a vertical line source with directivity characteristics computed from the various parameters. The result of radiation from the tunnel opening is shown as increases in sound level relative to the roadway alone in a contour map presented in the article as Fig. 26, shown below. Probst model increase in sound level at tunnel opening; no absorption in tunnel Institute of Noise Control Engineering The paper does not provide any validation data or comparisons with measurements. Instead, the author assumes the national road noise emission models that would be used to develop reference noise emissions and the room acoustics methods proposed are sufficiently validated such that no validation is necessary. L-

10 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM This model holds considerable promise as a way to identify appropriate sound power level to apply to a tunnel opening, since the model accommodates many variables. Using a model such as CadnaA or SoundPLAN, this method would provide a more accurate approach to tunnel opening modeling than would be possible with TNM, which does not allow users to specify source directivity. However, there are simpler ways to utilize the information presented in this article that could be beneficial to the highway noise analyst. L.3 Gaps or Weaknesses Identified A number of models for computing noise levels from tunnel openings have been presented and published over the past years or so. The most recent identified publication from Probst is comprehensive, thorough and based upon well-established methods, and therefore it holds significant promise as a model for serious consideration by this study team and others. The major weakness in the Probst methodology is that no true validation is presented. A significant challenge with obtaining high quality noise measurements near tunnel openings is that noise from the uncovered section of the roadway is almost always present in addition to noise from the opening itself. Therefore, determining the contribution from the tunnel alone is not possible through direct measurement. Modeling of the uncovered sections of roadway is required to estimate that contribution, which introduces uncertainty into the measurement conclusions. In addition, increases in sound level from tunnel openings can be small, on the order of a few decibels. This increases uncertainty in identifying the contribution from the opening itself. Perhaps as a result of these difficulties, very limited noise measurement and validation data were found in the published literature. The Takagi paper may provide the most data presently available; however, those data are not in a form that can be used conveniently. Therefore, we believe that additional measurements near tunnel openings could provide needed validation of models such as that of Probst. Measurements will also provide validation of more approximate methods that may be suggested for lower-precision needs, such as environmental document noise studies. L.4 Evaluation of Candidate Modeling Techniques As discussed above, one modeling technique that will allow for relatively precise modeling of noise from tunnel openings is that presented by Probst in his Noise Control Engineering Journal (NCEJ) article. The approach should have validation, since all indications suggest that it could be a predictive methodology, particularly if there is the potential of significant noise impact near tunnel openings, and abatement measures are needed. However, it may be more complex than many will be able to pursue. Particularly, those pursuing environmental document noise analysis and/or those without access to noise modeling programs such as CadnaA and SoundPLAN. In the development of recommended best modeling practices, the study team has tested and evaluated candidate modeling techniques that could be used to generate the approximate sound power levels at the tunnel opening, using TNM roadways and vehicles as the source, since it is not possible to directly specify sound power levels in TNM. The study team decided to use SoundPLAN s implementation of the Takagi model as our benchmark for evaluating the candidate modeling techniques described in the following sections. Even though it is not clear whether the Takagi model was compared to measurement data for a single vehicle passage or for a traffic stream, the approach was nevertheless validated in some manner and forms the basis of the tunnel opening algorithms in SoundPLAN. For this reason, it was adopted as our benchmark. L-6

11 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM L.4.1 Overview For the evaluation of these candidate modeling techniques, traffic noise levels were calculated using SoundPLAN s tunnel opening objects and algorithms. The SoundPLAN-calculated values were used as the baseline against which each modeling technique was evaluated. This process resulted in the development of methodologies to adjust the basic FHWA TNM output data to as closely as possible incorporate the effects of tunnel openings. The recommended best modeling practices for TNM users are based on the modeling technique that was found to yield the best agreement with the tunnel opening algorithms in SoundPLAN. The following parameters were included in each of the modeling techniques that were evaluated in this study: A single TNM road (1, meters long with. percent grade) located outside the tunnel with 3, automobiles, 1 medium trucks, and 1 heavy trucks per hour, all traveling at a speed of kilometers per hour; Pavement as default ground type everywhere; A x 7 matrix of receptors outside the tunnel at distances of 1, 2,, 1, and meters from the roadway centerline and at distances of 1,, 1, 2,, 1, and meters from the tunnel opening; Receptor elevations of 1. and 4. meters above ground level (AGL); Noise barriers at a height of.48 meters to represent the side walls of the tunnel; No absorption in the tunnel; and Tunnel openings of meters wide by 6 meters high and meters wide by 6 meters high. The study team generally focused the evaluation on tunnels that were and 1 meters in length; however, tunnel lengths of 1 meter and 1, meters also were evaluated in an attempt to understand the dependency of the calculated tunnel effect upon tunnel length. Before evaluating and testing the modeling techniques against SoundPLAN s tunnel opening algorithms, the team tested SoundPLAN s implementation of the TNM algorithms for the road outside the tunnel. Excellent agreement between SoundPLAN s implementation of the TNM algorithms and TNM itself was found for the simple straight road located outside the tunnel. Calculated traffic noise levels in SoundPLAN ranged from.1 dba less than to.2 dba greater than the noise levels calculated with TNM Version 2. at both 1. and 4. meters AGL. On average, SoundPLAN calculated noise levels were.1 dba higher than TNM-calculated noise levels for the x 7 receptor matrix at 1. meters AGL. At 4. meters AGL, SoundPLAN-calculated noise levels were within.1 dba of the TNM-calculated noise levels. Figure 1 provides a graph of the TNM-calculated noise levels as a function of the SoundPLANcalculated noise levels for the roadway outside the tunnel for the x 7 matrix of receptors at 1. meters AGL. Although we have not shown the graph, similar results were obtained for the x 7 matrix of receptors at 4. meters AGL. Note that the overall trends for the x 7 matrix of receptors at 4. meters AGL were very similar to the trends at 1. meters AGL. Consequently, the study team decided to show only the comparisons between TNM and SoundPLAN for the receptor matrix at 1. meters AGL in this Appendix. L-7

12 Calculated Leq (dba) for Road Outside Tunnel Only (FHWA TNM) Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM 7 Roadway Outside the Tunnel Calculated traffic noise levels at different distances from the tunnel opening Calculated Leq (dba) for Road Outside Tunnel Only (SoundPLAN) m from road 1 m from road m from road Figure 1 TNM-Calculated L eq Vs. SoundPLAN-Calculated L eq for the Roadway Outside the Tunnel for the x 7 matrix of receptors at 1. meters AGL Having demonstrated that SoundPLAN was appropriately implementing TNM s algorithms for the roadway outside the tunnel, the candidate modeling techniques were evaluated using SoundPLAN s calculated noise levels as a benchmark, as described below. For the evaluation of the following modeling techniques, the contributions from the road outside the tunnel were ignored, and calculated tunnel-only noise levels from FHWA-TNM Version 2. were compared to calculated tunnel-only noise levels from SoundPLAN. L.4.2 Perpendicular road across & just outside tunnel opening with a single road inside the tunnel This technique consisted of a perpendicular roadway across and just outside the tunnel opening to represent the reflected sound field from within the tunnel. This technique also included a single roadway within the tunnel to represent the contribution from the direct sound field, on the basis that receptors outside the tunnel will have direct lines-of-sight to portions of the road inside the tunnel. The geometry for this modeling technique is shown in Figure 2. The traffic volumes and speeds on each of the two tunnel-only roads matched the traffic volumes and speeds that were modeled for the road outside the tunnel. Using this modeling technique, TNM-calculated tunnel-only noise levels demonstrated poor agreement with the SoundPLAN-calculated levels and showed very little directionality as shown in the graphs of Figure 4 to Figure 6 (attached to the end of this Appendix). Figure 4 shows TNM and SoundPLAN tunnel-only noise levels for this modeling technique for the X 7 matrix of receptors at 1. meters AGL. 8 8 In Figure 4 to Figure 19, receptors are labeled using the notation shown in quotes Rec_X_Y : where X is the distance from the tunnel opening (parallel to the road) in meters; and Y is the perpendicular distance from the roadway in meters. See also Figure 2. In some figures the following text is appended to the receptor name Flr1 this text indicates that the receptor was modeled at a 1 st floor location; i.e. 1. meters AGL. L-8

13 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM Figure shows the difference between tunnel-only noise levels calculated with TNM and SoundPLAN. Figure 6 plots the calculated TNM tunnel-only noise levels against the SoundPLAN tunnel-only noise levels. Consequently, the team evaluated the separate contributions from the reflected field (i.e. from the perpendicular road across and just outside the tunnel opening) and the direct sound field (i.e. from the single road inside the tunnel). This supplemental analysis demonstrated that the directional characteristics of traffic noise radiating from the tunnel opening were not accurately represented by the perpendicular road across and just outside the tunnel opening. Figure 2 Plan view of TNM-modeled geometry for x 6 x m tunnel with perpendicular road across and just outside tunnel opening (with x 7 matrix of receptors) L.4.3 Perpendicular road across & just inside tunnel opening with a single road inside the tunnel The team then considered placing the perpendicular road across and just inside the tunnel opening. It was thought that the noise barriers representing the walls of the tunnel would more effectively attenuate noise from the perpendicular road and thereby introduce some directionality into the calculated results for the x 7 matrix of receptors. Although the TNM-calculated noise levels showed somewhat better agreement with SoundPLAN (considering the standard deviation of the differences between TNM and SoundPLAN), the TNM-calculated sound levels did not exhibit the anticipated directional characteristics of the tunnel opening for the receptors at either 1. meters AGL or 4. meters AGL. The results of this modeling technique are shown in the graphs of Figure 7 to Figure 9, which are attached to the end of this Appendix. L-9

14 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM L.4.4 Three parallel and evenly spaced roads inside the tunnel each with 1X volume of road outside This modeling technique considered three evenly-spaced roads inside the tunnel, between the noise barriers that were included in the model to represent the walls of the tunnel. Each road inside the tunnel was modeled with the same traffic volumes and speeds as the road outside the tunnel so in effect, the traffic volumes inside the tunnel were 3 times the traffic volumes on the road outside the tunnel. Figure 3 shows a detail of a plan view of the modeled geometry for a x 6 x meter tunnel within TNM. Figure 3 Close-up of plan view showing TNM-modeled geometry for x 6 x m tunnel with three parallel and evenly spaced roads inside the tunnel (with a subset of x 7 matrix of receptors) Four tunnel lengths (1,, 1, and 1, meters) were evaluated for this modeling technique to understand the extent to which tunnel length influences the amount of noise radiated from the tunnel opening. Figure 1 shows SoundPLAN-calculated noise levels radiated from a x 6 meter tunnel opening for each of the four lengths. Based on the results in this figure, it is apparent that the length of the tunnel affects the noise radiated from the tunnel opening. The SoundPLAN calculations show that noise emissions increase with increasing tunnel length up to a point. Over the range of tunnel lengths from to 1 meters, the additional tunnel length adds approximately.3 db of radiated noise per meter. At greater tunnel lengths, over the range from 1 to 1, meters, the additional tunnel length adds only.2 db of radiated noise per meter. The results of this modeling technique are presented in the graphs of Figure 11 to Figure 13, which are attached to the end of this Appendix. Figure 11 shows TNM and SoundPLAN tunnel-only noise levels for this modeling technique for the receptors at 1. meters AGL. Figure 12 shows the difference between tunnel-only noise levels calculated with TNM and with SoundPLAN and Figure 13 plots the calculated TNM tunnel-only noise levels against the SoundPLAN tunnel-only noise levels. The results of this modeling technique were judged to be acceptable for both tunnel widths at a length of meters; however, at a tunnel length of 1 meters, the TNM-calculated tunnel effect was approximately 4 db lower than the tunnel effect calculated with SoundPLAN. Determination: The results of this modeling technique were judged to be acceptable for both the -meter and the -meter tunnel width at a length of meters, and so this modeling technique is recommended for tunnel lengths between and meters. L-1

15 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM L.4. Three parallel and evenly spaced roads inside the tunnel each with 2.X volume of road outside This modeling technique was evaluated to address the 4 db under prediction that was previously observed for the 1 meter length tunnel. Since the calculated tunnel-only noise levels demonstrated the expected directionality pattern using the previous modeling technique, the 4 db under prediction was addressed by increasing the traffic volumes on the three roads inside the tunnel by a factor of 2. times the traffic volume on the road outside the tunnel. This upward adjustment effectively increases the traffic volumes inside the tunnel by a total of 7. times the traffic on the road outside the tunnel. The graphs of Figure 14 to Figure 16, which are attached at the end of this Appendix, show the results of the evaluation for this candidate modeling technique. Determination: The results for the 1 meter long tunnel were judged to be acceptable, and so this modeling technique is recommended for tunnel lengths greater than meters. L.4.6 Four parallel and evenly spaced roads inside the tunnel each with 1.9X volume of road outside The previous modeling technique is easily used for cases with a single road on the outside of the tunnel. Realizing that there may be real-world situations for which two roads may be modeled outside the tunnel, e.g. to accommodate two directions of travel, this modeling technique was evaluated to provide the user with a more straight-forward method of distributing the traffic volumes across each of the roads inside the tunnel. This modeling technique uses 1.9 times the traffic volume(s) on the road(s) outside the tunnel on each of the four roads inside the tunnel. This technique effectively increases the traffic volumes inside by a total of 7.6 times the traffic on the road outside the tunnel. As expected, the results of this modeling technique closely matched the results of the previous technique that utilized three roads inside the tunnel each with 2. times the traffic on the road outside the tunnel. The graphs of Figure 17 to Figure 19, which are attached to the end of this Appendix, show the results for the evaluation of this candidate modeling technique. Determination: This modeling technique may be used interchangeably with the previous 3-road modeling technique. This 4-road modeling technique also was judged to be suitable for tunnel lengths greater than meters. L.4.7 Statistics of the differences between TNM-calculated noise levels and SoundPLAN-calculated noise levels Table 1 provides a summary of descriptive statistics for the differences between the TNM and SoundPLAN tunnel-only noise levels for the modeling techniques that were evaluated in this study. Note that Tables 1 to appear at the end of this appendix, after Figures 4 to 23. L. Tunnel Effects Based on the results of the previous section, the study team identified preferred modeling techniques for use in the FHWA TNM as follows: 1. For tunnels less than meters in length, there is no need to model radiated noise, since the effects are negligible for this geometry; 2. For short tunnels (between and meters in length) with a single road outside the tunnel model three parallel and evenly spaced roadways inside the tunnel each with 1X the volume of the road outside the tunnel. L-11

16 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM 3. For longer tunnels (greater than meters in length) with a single road outside the tunnel model three parallel and evenly spaced roadways inside the tunnel each with 2.X the volume of the road outside the tunnel. 4. For longer tunnels with two roads outside the tunnel model four parallel and evenly spaced roads inside the tunnel each with 1.9X the volume of the road outside the tunnel. Note that the TNM- and SoundPLAN-calculated noise levels presented in the previous section and shown in the graphs of Figure 4 to Figure 19 only include the contributions from the traffic noise sources inside the tunnel, i.e. sources associated with the direct sound field and the reflected sound field that are radiated from the tunnel opening. Table 2 to Table compare the tunnel effect that was calculated using the SoundPLAN-Takagi model with the tunnel effect calculated using the specified modeling technique within FHWA TNM Version 2.. The tunnel effect is simply the increase due to radiated noise from the tunnel opening. The tables show the tunnel effect for receptors along a roadway with a line of sight to the tunnel opening at heights of 1. and 4. meters above ground. As shown in those tables, when the contribution from the road outside the tunnel is combined with tunnelradiated noise, the overall effect ranges from to dba. In general, the tunnel effect may be as much as dba in close proximity to long tunnels and less than 1 dba at distances of 1 meters, or more, from the centerline of the roadway. The tunnel effects in Table 2 to Table were arithmetically averaged to generate the tabulated values in the lookup table in the main body of the report. L.6 Traffic Noise Measurements near a Tunnel Opening With the cooperation of the Massachusetts Department of Transportation, the study team conducted traffic noise measurements in the vicinity of the Thomas O. O'Neill, Jr. Tunnel, south of Kneeland Street in Boston, Massachusetts. Figure shows an aerial image of the southbound lanes of I-93 coming out of the tunnel. Figure 21 and Figure 22 show photographs of the tunnel opening and I-93 southbound. Note the presence of a reflective surface on the left hand side of the photograph in Figure 21. That photograph also shows the top of a retaining wall on the right hand side. The photograph of Figure 23 shows concrete pavement with transverse tining on I-93 southbound coming out of the tunnel. The study team had intended to validate the recommended modeling technique for tunnel radiated traffic noise using measurement data obtained at this site. However, in hindsight, this Boston site is likely to be a poor validation site. Multiple non-traffic and non-tunnel effects from reflective surfaces, pavement surface, and expansion joints would likely mask the effect of the tunnel radiated noise that we are attempting to quantify in this study. This observation is underscored when the relatively small tunnel effects (from to dba) shown in Table 2 to Table are considered. The study team recommends consideration of a range of alternate sites to validate the recommended modeling techniques for tunnel openings as the focus of future research. L-12

17 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM x 6 x m Tunnel at 1. m AGL x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL Appendix L - Additional Figures x 6 x 1m Tunnel at 1. m AGL x 6 x m Tunnel at 1. m AGL re: SP x 6 x m Tunnel at 1. m AGL re: SP Figure 4 TNM and SoundPLAN tunnel-only noise levels for perpendicular road across & just outside tunnel opening with a single road inside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL 1 x 6 x 1m Tunnel at 1. m AGL re: SP - -1 x 6 x 1m Tunnel at 1. m AGL re: SP Figure Plots of TNM tunnel-only noise level minus SoundPLAN tunnel-only noise level for perpendicular road across & just outside tunnel opening with a single road inside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL L-13

18 Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal m from road 1 m from road m from road m from road 1 m from road m from road x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal m from road 1 m from road m from road Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal m from road 1 m from road m from road Figure 6 FHWA TNM tunnel-only noise levels compared to SoundPLAN tunnel-only noise levels for perpendicular road across & just outside tunnel opening with a single road inside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL L-14

19 x 6 x m Tunnel at 1. m AGL Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL x 6 x m Tunnel at 1. m AGL 1 re: SP - -1 x 6 x m Tunnel at 1. m AGL re: SP Figure 7 TNM and SoundPLAN tunnel-only noise levels for perpendicular road across & just inside tunnel opening with a single road inside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL 1 x 6 x 1m Tunnel at 1. m AGL re: SP x 6 x 1m Tunnel at 1. m AGL re: SP - -1 Figure 8 Plots of TNM tunnel-only noise level minus SoundPLAN tunnel-only noise level for perpendicular road across & just inside tunnel opening with a single road inside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL L

20 Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal and the Road Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal and the Road m from road 1 m from road m from road m from road 1 m from road m from road x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal and the Road Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal and the Road m from road 1 m from road m from road m from road 1 m from road m from road Figure 9 FHWA TNM tunnel-only noise levels compared to SoundPLAN tunnel-only noise levels for perpendicular road across & just inside tunnel opening with a single road inside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL L-16

21 Rec_1_1 Rec 1 Rec_1_1 Rec_2_1 Rec 1 Rec_1_1 Rec 1 Rec_1_2 Rec 2 Rec_1_2 Rec_2_2 Rec 2 Rec_1_2 Rec 2 Rec_1_ Rec Rec_1_ Rec_2_ Rec Rec_1_ Rec Rec_1_1 Rec 1 Rec_1_1 Rec_2_1 Rec 1 Rec_1_1 Rec 1 Tunnel-Only Leq (dba) Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM SoundPLAN-Calculated Tunnel-Only Noise Levels at 1. m AGL for Different Tunnel Lengths 1 meter meters 1 meters 1, meters Figure 1 SoundPLAN-calculated tunnel-only noise levels as a function of tunnel length for a x 6 meter opening for receptors at 1, 2,, and 1 meters from the centerline of the road and at distances of 1,, 1, 2,, 1, and meters from the tunnel opening x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL Figure 11 TNM and SoundPLAN tunnel-only noise levels for 3 parallel and evenly spaced roads inside the tunnel with 1X the volume of the road outside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL L-17

22 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL 1 re: SP 1 re: SP x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL 1 re: SP 1 re: SP Figure 12 Plots of TNM tunnel-only noise level minus SoundPLAN tunnel-only noise level for 3 parallel and evenly spaced roads inside the tunnel with 1X the volume of the road outside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL L-18

23 Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal m from road 1 m from road m from road m from road 1 m from road m from road x 6 x m Tunnel at 1. m AGL Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal x 6 x 1m Tunnel at 1. m AGL Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal m from road 1 m from road m from road m from road 1 m from road m from road Figure 13 FHWA TNM tunnel-only noise levels compared to SoundPLAN tunnel-only noise levels for 3 parallel and evenly spaced roads inside the tunnel with 1X the volume of the road outside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL L-19

24 x 6 x m Tunnel at 1. m AGL Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL x 6 x m Tunnel at 1. m AGL re: SP x 6 x m Tunnel at 1. m AGL re: SP Figure 14 TNM and SoundPLAN tunnel-only noise levels for 3 parallel and evenly spaced roads inside the tunnel with 2.X the volume of the road outside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL 1 x 6 x 1m Tunnel at 1. m AGL re: SP x 6 x 1m Tunnel at 1. m AGL re: SP - -1 Figure Plots of TNM tunnel-only noise level minus SoundPLAN tunnel-only noise level for 3 parallel and evenly spaced roads inside the tunnel with 2.X the volume of the road outside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL L-

25 Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal m from road 1 m from road m from road Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal m from road 1 m from road m from road x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal m from road 1 m from road m from road Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal m from road 1 m from road m from road Figure 16 FHWA TNM tunnel-only noise levels compared to SoundPLAN tunnel-only noise levels for 3 parallel and evenly spaced roads inside the tunnel with 2.X the volume of the road outside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL L-21

26 x 6 x m Tunnel at 1. m AGL Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL x 6 x m Tunnel at 1. m AGL re: SP x 6 x m Tunnel at 1. m AGL re: SP Figure 17 TNM and SoundPLAN tunnel-only noise levels for 4 parallel and evenly spaced roads inside the tunnel with 1.9X the volume of the road outside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL 1 x 6 x 1m Tunnel at 1. m AGL re: SP x 6 x 1m Tunnel at 1. m AGL re: SP - -1 Figure 18 Plots of TNM tunnel-only noise level minus SoundPLAN tunnel-only noise level for 4 parallel and evenly spaced roads inside the tunnel with 1.9X the volume of the road outside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL L-22

27 Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Calculated Leq (dba) for Tunnel Only (FHWA TNM) Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM x 6 x m Tunnel at 1. m AGL Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal x 6 x 1m Tunnel at 1. m AGL Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal m from road 1 m from road m from road m from road 1 m from road m from road x 6 x m Tunnel at 1. m AGL x 6 x 1m Tunnel at 1. m AGL Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal Calculated Tunnel-only noise levels at Different Distances from the Tunnel Portal m from road 1 m from road m from road m from road 1 m from road m from road Figure 19 FHWA TNM tunnel-only noise levels compared to SoundPLAN tunnel-only noise levels for 4 parallel and evenly spaced roads inside the tunnel with 1.9X the volume of the road outside the tunnel at distances of 1,, 1, 2,, 1, and meters from the tunnel opening and 1, 2,, and 1 meters from the road centerline and 1. meters AGL L-23

28 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM Imagery 13 Google Figure Traffic noise measurement locations in the vicinity of the Thomas O. O'Neill, Jr. Tunnel (I-93) in Boston, Massachusetts Source: HMMH Figure 21 Photograph of I-93 southbound coming out of the Thomas O. O'Neill, Jr. Tunnel, south of Kneeland Street in Boston, Massachusetts L-24

29 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM Source: HMMH Figure 22 Microphone location above and adjacent to the portal of the Thomas O. O'Neill, Jr. Tunnel in Boston, Massachusetts Source: HMMH Figure 23 Pavement on I-93 southbound south of the Thomas O. O'Neill, Jr. Tunnel in Boston, Massachusetts L-2

30 Final Technical Report: NCHRP 2-34 Supplemental Guidance on the Application of FHWA s TNM Appendix L - Additional Tables Table 1 Summary of descriptive statistics for differences between TNM-calculated and SoundPLAN-calculated tunnel-only noise levels for the modeling techniques that were evaluated TNM One (1) Perpendicular Road Just Outside Tunnel (w/ 1X Volume of Road Outside) Geometry: Length TNM re: SP in db for a X 6 m Portal TNM re: SP in db for a X 6 m Portal Std. Std. (m) Maximum Average Minimum Maximum Average Minimum Dev. Dev TNM Geometry: One (1) Perpendicular Road Just Inside Tunnel (w/ 1X Volume of Road Outside) Length TNM re: SP in db for a X 6 m Portal TNM re: SP in db for a X 6 m Portal (m) Maximum Average Minimum Std. Dev. Maximum Average Minimum TNM Geometry: Three (3) Parallel Roads Inside Tunnel (each with 1 X Volume of Road Outside) Length TNM re: SP in db for a X 6 m Portal TNM re: SP in db for a X 6 m Portal (m) Maximum Average Minimum Std. Dev. Maximum Average Minimum TNM Geometry: Three (3) Parallel Roads Inside Tunnel (each with 2. X Volume of Road Outside) Length TNM re: SP in db for a X 6 m Portal TNM re: SP in db for a X 6 m Portal (m) Maximum Average Minimum Std. Dev. Maximum Average Minimum TNM Geometry: Four (4) Parallel Roads Inside Tunnel (each with 1.9 X Volume of Road Outside) Length TNM re: SP in db for a X 6 m Portal TNM re: SP in db for a X 6 m Portal (m) Maximum Average Minimum Std. Dev. Maximum Average Minimum Std. Dev. Std. Dev. Std. Dev. Std. Dev. L-26