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26 The Six-Lane Highway Scenario To illustrate application of the methodology developed in this research, the six-lane new highway construction scenario used in the LCCA (Figure 10) was used to evaluate different noise exposure cases representing those of neighborhoods in three states. For this purpose, a simple flat geometry was assumed, the rows of buildings and other features were not accounted for in the analysis, and the traffic conditions were those used in the LCCA. These analyses will illustrate the application of the approach to different impact scenarios of highway projects with the same design and details. The net present value (NPV) costs developed in the original LCCA were used with some modifica- tions to account for different barrier heights that were consid- ered. Noise abatement analysis was conducted loosely based on the traffic noise policies of the states from which the exposure case was taken. TNM-predicted noise levels were computed for the pave- ments and levels shown in Figures 12 and 13 as well as other pavement types using the SRTT OBSI data. The spectra and longevity data for the open-graded rubberized asphalt con- crete [RAC(O)] pavement, shown in Figure 14, were taken from Caltrans Quieter Pavement Research work performed on LA 138 (21). The values for the ARFC pavement shown in Figure 15 correspond to levels and longevity rates found in the ADOT QPPP research (18, 51). The levels and longevity rates for the longitudinally tined PCC pavement were derived from the Caltrans Quieter Pavement Research work on the Mojave Bypass (58), the data for the ground PCC pavement were taken from test sections measured in Kansas on US 69 (59), and data for the random transversely tined pavement were from I-70 in Ohio (48); all of these are shown in Fig- ure 16. The overall OBSI levels and the TNM-predicted lev- els at different distances from the highway for new and aged pavements are presented in Table 5. These example cases are specific to the six-lane new high- way case and would not apply to other highway configura- tions. As the number of lanes increase or decrease, the cost of quieter pavement options relative to barriers will change while achieving about the same noise reduction. Also, if receptors are equally located on both sides of the highway, the cost for barri- ers will be double than if receptors were only on one side, but pavement cost would remain the same. Also these examples assumed that the length of the barriers and quieter pavement will coincide, which would not necessarily occur in practice. The TNM Average Pavement is used in the LCCA although it does not provide a specific design for which a cost can be defined. For these examples, traffic noise levels are presented for TNM Average Pavement with cost based on a generic HMA pavement without an added cost for acoustic performance. The rehabilitation cycle for this pavement is assumed to be 15 years for performance issues other than noise. In practice, a SHA would base the analysis on actual, specific pavement cost and acoustic performance. The acoustic performance of this pave- ment would be documented with OBSI data. A summary of the LCCA results for the HMA pavement and other pavements and barriers used in these cases is given in Table 6 (detailed infor- mation on the LCCA is provided in Appendix C). The NPV of the 12 ft high barriers was determined from the cost difference between the options with and without barriers, yielding an NPV of $3,685,000. This value was scaled appropriately for different heights and for the use of a barrier on just one side of the high- way as needed. These estimated NPVs were then added to the NPV of the pavement alone. For the PCC pavements, it was assumed that texturing does not affect the life-cycle cost of these pavements. However, grinding was considered as a method of producing a quieter pavement initially after construction and as a rehabilitation method after 20 years of service. The costs for RAC(O) and ARFC pavements were determined to be similar enough such that the NPV of either type could be used. Example 1: High-Density Case This case is patterned after a neighborhood in Southern California along the Garden Grove Freeway (State Route 22) in the City of Garden Grove (Figure 17). In this case, one row of C H A P T E R 4 Examples of Methodology Application
27 receptors is about 63 ft away from the center of the near through lane of travel and another row is at about 235 ft. The exist- ing TNM results with receptor locations being approximated as 50 ft and 250 ft away were used for the analysis. The length of freeway shown is about 1,450 ft with 16 residences in each row. It was assumed that this pattern is repeated for at least 1 mi; thus, for the 1 mi project, receptor density is highâ72 receptors in each rowâand a barrier will be built on one side of the road. The following pavement alternatives were considered: ⢠HMA pavement with a 15-year rehabilitation cycle perform- ing as TNM Average Pavement (designated as âHMAâ in the following tables) ⢠HMA pavement constructed with a 1 in. RAC(O) surface layer replaced every 9 years (designated âRAC(O)â in the following tables) ⢠PCC pavement with longitudinal tines and rehabilitation every 20 years by grinding (designated as âLT PCCâ in the following tables) Source: Data from Donavan et al. (18), Scofield and Donavan (51). 70 75 80 85 90 95 100 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 1/3 Octave Band Center Frequency, Hz So un d In te ns ity L ev el , d BA New AFRC 7-Year Old ARFC 8-Year Old ARFC 9-Year Old ARFC Figure 15. OBSI one-third octave band spectra for ARFC pavement. Source: Data from Thornton et al. (20). 70 75 80 85 90 95 100 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 1/3 Octave Band Center Frequency, Hz So un d In te ns ity L ev el , d BA New RAC(O) 7 Year Old RAC(O) 8 Year Old RAC(O) 9 Year Old RAC(O) Figure 14. OBSI one-third octave band spectra for RAC(O) pavement.
28 Source: Data from Donavan and Rymer (58), Donavan (59), Illingworth & Rodkin, Inc. (48). 75 80 85 90 95 100 105 110 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 1/3 Octave Band Center Frequency, Hz So un d In te ns ity L ev el , d BA New Ground New Long. Tine Old Long. Tine Rand. Trans. Tine Figure 16. OBSI one-third octave band spectra for PCC pavements. Level and Distance Pavement Type, Texture, and Age (Levels in dBA) RAC(O) ARFC Long. Tine PCC Ground PCC Random Trans. Tine PCCNew 9 yr New 9 yr New Aged OBSI 96.0 100.2 95.3 100.6 102.4 105.1 99.6 108.6 TNM @ 25 ft 74.4 77.5 74.3 78.7 79.0 81.9 76.8 85.0 TNM @ 50 ft 72 75.1 72.5 76.9 76.7 79.5 74.4 82.5 TNM @ 100 ft 68.9 71.9 70.0 74.4 73.4 76.3 71.3 79.3 TNM @ 175 ft 65.6 68.4 67.5 71.8 69.9 72.7 67.9 75.7 TNM @ 250 ft 63.1 65.7 65.2 69.4 67.2 69.9 65.3 72.8 Table 5. OBSI and corresponding TNM predictions for different pavements. Pavement Type (Rehabilitation Cycle) with & without 12 ft Barrier Agency Cost ($000) User Cost ($000) Total Cost ($000) Abatement Cost ($000) HMA Construction (15 yr)âBaseline 1 6,937 10 6,947 0 HMA Construction + Barrier 10,763 10 10,773 3,826 RAC(O)/HMA (7 yr) 9,624 25 9,649 2,687 RAC(O)/HMA (7 yr) + Barrier 13,450 25 13,475 6,513 RAC(O)/HMA (8 yr) 8,985 18 9,003 2,049 RAC(O)/HMA (8 yr) + Barrier 12,811 18 12,829 5,875 RAC(O)/HMA (9 yr) 8,539 21 8,560 1,603 RAC(O)/HMA (9 yr) + Barrier 12,365 21 12,386 5,429 PCC ConstructionâBaseline 2 7,925 9 7,934 0 PCC + Barrier 11,751 9 11,760 3,826 PCC + Initial Grinding 9,273 9 9,282 1,348 PCC + Initial Grinding + Barrier 13,099 9 13,108 5,174 Table 6. Summary of NPV costs used in example cases.
29 ⢠PCC pavement with initial ground texture and rehabili- tation every 20 years by grinding (designated as âGround PCCâ in the following tables) ⢠PCC pavement with random transverse tines and a 20-year rehabilitation cycle (designated as âRT PCCâ in the follow- ing tables) Although transversely tined texture is not typically used in California for on-grade pavements, it is included in this example as an alternative. For each pavement design, one or two barrier designs were considered; these barriers were assumed to be 1 mi long, of different heights, and placed on the outside edge of the near shoulder. The analysis for the different pavement alternatives with- out barriers is shown in Table 7. The noise impacts were assessed by applying Caltrans and WSDOT criteria (60, 61) that define a benefited receptor as obtaining a 5 dB reduction and use a noise reduction design goal of 7 dB for at least one first row receptor and the Noise Abatement Criteria (NAC) of 66 dBA. Table 7 shows that although the predicted level at 50 ft ranges from 72 to 83 dBA, all receptors are impacted. At 250 ft, all receptors are impacted by all pavement alternatives except the RAC(O) and ground PCC. At the end of the respec- tive rehabilitation cycles, the RAC(O) would reach the impact threshold and ground PCC would exceed it (when consider- ing a 3 dB increase for the LT PCC). In terms of performance, the amount of reduction for the RAC(O) and ground PCC depends on the baseline pavement. For receptors at 50 ft, the initial reduction for the RAC(O) is 5 dB relative to HMA and LT PCC, and 11 dB relative to RT PCC. These reductions meet the 5 dB feasibility criteria relative to each of the other three pavement types. After 9 years, a reduction of 5 dB or greater would only exist relative to RT PCC. For receptors at 50 ft, the reduction for the ground PCC is 3 dB relative to HMA and LT PCC, which does not meet current feasibility criteria, but the reduction is 9 dB relative to RT PCC. The RAC(O) and ground PCC would achieve a 7 dB design goal only relative to RT PCC. Source: Google Earth © 2011 Google Barrier Figure 17. Aerial photograph of a portion of the Garden Grove Freeway in Garden Grove, California. Pavement 72 Receptors at 50 ft 72 Receptors at 250 ft Total Number of Impacts Agency NPV Cost ($000) Level (dBA) Impacts Level (dBA) Impacts HMA 77 72 67 72 144 6,937 RAC(O) 72 72 63 0 72 8,539 LT PCC 77 72 67 72 144 7,925 Ground PCC 74 72 65 0 72 9,273 RT PCC 83 72 73 72 144 7,925 9-yr RAC(O) 75 72 66 72 144 8,539 20-yr LT PCC 80 72 70 72 144 7,925 Table 7. Predicted traffic noise levels, number of impacted receptors, and NPV costs for Example 1.
30 The use of 8 ft high barriers on one side of the highway was considered for all pavements and 12 ft high barriers were also considered for the HMA and RT PCC pavements. The calculated traffic noise levels at 50 ft and 250 ft together with the overall pavementâbarrier system noise reductions relative to the HMA, LT PCC, and RT PCC pavements are shown in Table 8. For receptors at the 50 ft distance, the lowest absolute levels were for the HMA with a 12 ft barrier at 65 dBA followed by the RAC(O) with an 8 ft barrier at 66 dBA. Both the HMA with a 12 ft barrier and the RAC(O) with an 8 ft barrier pro- duced the lowest levels at 60 dBA for receptors at the 250 ft distance. The insertion loss of the barriers ranged from 6 to 13 dB at 50 ft. To assess feasibility, the noise reduction rela- tive to the baseline pavement was used instead of the barrier insertion loss alone. Relative to the LT PCC and HMA base- lines, all alternatives except ground PCC with no barrier and RT PCC with a 12 ft barrier are acoustically feasible and pro- vide benefit. For receptors at 250 ft, the insertion losses range from 4 to 7 dB. In terms of noise reduction at 250 ft relative to the HMA and LT PCC baselines, the RT PCC baseline with a 12 ft barrier does not provide benefit (it showed negative noise reduction), but the RAC(O) and ground PCC with 8 ft barriers and HMA with 12 ft barriers all provide benefit. Also, the RAC(O) pavement with an 8 ft barrier provides benefit after 9 years. Relative to the RT PCC baseline, all alternatives provide benefit at 250 ft. Relative to the HMA and LT PCC baselines, the RAC(O) without a barrier does not achieve a design goal of 7 dB, but with an 8 ft barrier, it achieves the goal for the first row of receptors. Other alter- natives that did not meet a 7 dB design goal relative to the HMA and LT PCC baselines are the ground PCC without a barrier, 20-year-old LT PCC with an 8 ft barrier, and RT PCC with a 12 ft barrier. The information presented in this section can be used to evaluate the acoustic feasibility and reasonableness perfor- mance for each alternative relative to the design goal. For the reasonableness evaluation, WSDOT uses a base barrier cost of $51.61/ft2 and Caltrans uses actual design costs. For LCCA, use of actual design costs is preferred but estimated costs may be used if actual costs are not available; $51.61/ft2 is used in this example (compared to the $27 national average). For cost allowance, WSDOT uses a graduated scale that increases the cost allowance as the noise-level reduction increases. Cal- trans uses a flat allowance of $55,000 per benefited receptor. To calculate the reasonableness allowance for this example, the receptors are only located on one side of the highway as shown in Figure 17. Using the results shown in Table 8, the number of benefited receptors for each alternative was estimated and is presented in Table 9 for assumed baseline noise levels of HMA or LT PCC. With only two groups of the receptors, the number of benefited receptors is either 72 or 144 depending on whether a feasible reduction was obtained at the 250 ft distance. Also shown in Table 9 are the NPV for the project together with the NPV for abatement (i.e., the cost due to quieter pavement, barriers, or a combination of the two). For each case, the NPV for the abate- ment is calculated relative to the NPV of the HMA pavement (without an added abatement). The acoustic performance of this pavement was taken to be that of TNM Average Pavement. The NPV of abatement for the PCC alternatives is also shown relative to a baseline of PCC pavement without abatement. For this analysis, the differences of NPV with and without abatement were compared to the reasonableness allowances Pavement Type and Barrier Height Receptors at 50 ft Receptors at 250 ft N oi se L ev el (d BA ) B ar rie r I L (dB ) dB Noise Reduction Relative to: N oi se L ev el (d BA ) B ar rie r I L (dB ) dB Noise Reduction Relative to: H M A [7 7 d BA ] LT P CC [7 7 d BA ] R T PC C [8 3 d BA ] H M A [6 7 d BA ] LT P CC [6 7 d BA ] R T PC C [7 3 d BA ] HMA + 8 ft 69 8 8 8 14 63 4 4 4 10 HMA + 12 ft 65 12 12 12 18 60 7 7 7 13 RAC(O) 72 n/a 5 5 11 63 n/a 4 4 10 RAC(O) + 8 ft 66 6 11 11 17 60 3 7 7 13 LT PCC + 8 ft 69 8 8 8 14 63 4 1 1 7 Ground PCC 74 n/a 3 3 9 65 n/a 2 2 8 Ground PCC + 8 ft 67 7 10 10 16 62 3 5 5 11 RT PCC + 12 ft 74 9 3 3 9 68 5 1 1 5 9-yr RAC(O) 75 n/a 2 2 8 66 n/a 1 1 7 9-yr RAC(O) + 8 ft 68 8 9 9 15 62 4 5 5 11 20-yr LT PCC + 12 ft 72 8 5 5 11 66 4 1 1 7 Table 8. Traffic noise levels, barrier insertion loss, and overall system noise reduction for Example 1.
31 calculated with WSDOT and Caltrans methods; the NPV was below the allowed amount for all cases except for the ground PCC pavement without a barrier and the random transver- sally tined PCC pavement. In these cases, the noise reduction relative to the predicted noise levels for the HMA and LT PCC pavements shown in Table 8 was less than the required 5 dB minimum reduction. However, if a baseline noise level of RT PCC pavement is assumed, a 12 ft high barrier provides a 5 and 9 dB insertion loss at 250 and 50 ft, respectively, and the grind- ing produces a tireâpavement noise reduction of 8 and 9 dB. With this baseline, both options would be reasonable for cost. Based on a design goal criterion of 7 dB, the RAC(O) without the 8 ft barrier would not be reasonable. Acoustic feasibility, cost reasonableness, and ability to meet the design goals of Caltrans and WSDOT are summarized in Table 10 for all of the pavementâbarrier alternatives using Table 9. Predicted noise levels with abatement, number of benefited receptors, NPV costs, and reasonable allowances for various abatement scenarios (receptors on one side). Pavement Type and Barrier Height Predicted Noise Level (dBA) N um be r o f B en ef ite d R ec ep to rs To ta l P ro jec t N PV ($ 00 0) NPV for Noise Abatement Relative to Ca ltr an s R ea so na bl en es s A llo w an ce ($ 00 0) W SD O T Re as on ab le ne ss A llo w an ce ($ 00 0) R ec ep to rs a t 17 5 ft R ec ep to rs a t 37 5 ft H M A B as el in e ($0 00 ) PC C Ba se lin e ($0 00 ) HMA + 8 ft 69 63 72 9,374 2,438 3,960 5,126 HMA + 12 ft 65 60 144 10,593 3,657 7,920 7,978 RAC(O) 72 63 72 8,539 1,603 3,960 5,126 RAC(O) + 8 ft 66 60 144 10,977 4,041 7,920 7,978 LT PCC + 8 ft 69 63 72 10,363 3,426 2,429 3,960 5,126 Ground PCC 74 65 0 9,273 2,337 1,339 0 0 Ground PCC + 8 ft 67 62 1441 11,711 4,774 3,777 7,9201 7,9781 RT PCC + 12 ft 74 68 0 11,582 4,645 3,648 0 0 9-yr RAC(O) 75 66 0 8,539 1,603 0 0 9-yr RAC(O) + 8 ft 68 62 144 10,977 4,041 3,043 7,920 7,978 20-yr LT PCC + 8 ft 72 66 72 10,363 3,426 2,429 3,960 5,126 1 Relative to RT PCC baseline only, not for HMA or LT PCC. Pavement Type and Barrier Height Caltrans WSDOT Ef fe ct iv en es s ( dB ) Cost Difference ($000) Relative to Fe as ib le Co st Re as on ab le D es ig n G oa l Fe as ib le Co st Re as on ab le D es ig n G oa l H M A PC C HMA + 8 ft Y Y Y Y Y Y 4 835 HMA + 12 ft Y Y Y Y Y Y 0 2,054 RAC(O) Y Y N Y Y N 7 0 RAC(O) + 8 ft Y Y Y Y Y Y 1 2,438 LT PCC + 8 ft Y Y Y Y Y Y 4 1,823 1,090 Ground PCC N N N N N N 9 734 0 Ground PCC + 8 ft Y Y Y Y Y Y 2 3,171 2,438 RT PCC + 12 ft Y1 Y1 Y1 Y1 Y1 Y1 9 3,042 2,309 9-yr RAC(O) N N N N N N 10 0 9-yr RAC(O) + 8 ft Y Y Y Y Y Y 3 2,438 20-yr LT PCC + 8 ft Y Y N Y Y N 7 1,823 1,090 1 Relative to RT PCC baseline only, not for HMA or LT PCC. Table 10. Assessment of options under Caltrans and WSDOT policies for Example 1.
32 each agencyâs criteria. Effectiveness as indicated by the differ- ence between the lowest absolute level for any of the alterna- tives and the level for a specific alternative and the additional cost relative to the lowest cost alternative are also shown to allow consideration of cost and effectiveness. The lowest NPV cost is the RAC(O) with no barrier, which is also acoustically feasible and cost reasonable (at least initially). However, this alternative does not provide the design goal of 7 dB reduction, is not as effective as some of the other alternatives in produc- ing low overall traffic noise levels, and does not meet either the feasibility or cost-reasonableness criterion at the end of the 9-year rehabilitation cycle. The next least expensive alter- native is ground PCC without a barrier; it is also one of the least effective alternatives and it does not provide an acoustic feasibility level of 5 dB. HMA with an 8 ft barrier is the next least expensive option; it meets a 5 dB feasibility and 7 dB rea- sonableness design criteria. However, the most effective solu- tion is the HMA with a 12 ft barrier followed closely by the RAC(O) with an 8 ft barrier. These two alternatives produce twice as many benefited receptors as the HMA with an 8 ft barrier but their NPV costs are higher than the HMA with the 8 ft barrier; both alternatives are well within the allowances for Caltrans and WSDOT. The LT PCC with the 8 ft barrier is a viable option that meets all the criteria and has the lowest cost of all PCC alternatives and effectiveness similar to that of the HMA with 8 ft barrier but at a somewhat higher cost. LT PCC could be further optimized by increasing the barrier height to increase effectiveness without adversely affecting its cost advantage over the other PCC options. The cost and effectiveness of the RT PCC with 12 ft barrier is not as good as that of LT PCC with 8 ft barrier and it is feasible and cost rea- sonable and meets the design goal only when it is compared to a baseline of the RT PCC pavement. When considering effectiveness in the selection process, trade-offs will be required. For example, HMA with both 8 ft and 12 ft barriers meet the feasible and reasonable criteria, but HMA with a 12 ft barrier performs better for effectiveness at a higher cost. Similarly, LT PCC with an 8 ft barrier is not as effective as ground PCC with an 8 ft barrier, but it has a lower NPV (about $1,350,000 less). In actual agency decisions, other considerationsâsuch as blocking the view of truck exhaust stacks (e.g., 13 ft barriers for WSDOT), highway/ pavement design practices, exposure to higher noise levels, and the opinions of residents affected by the abatementâ may also affect the selection process. The scenarios presented in Table 9 consider receptors and barriers on only one side of the highway. If receptors were mirrored on the other side of the highway, the NPVs for the barrier cases would increase together with corresponding increases in the reasonableness allowances as the number of benefited receptors is doubled. Table 11 shows the adjusted NPVs and allowances. In spite of the increased NPV for the barriers and allowance for receptors on both sides, all results in Table 10 will apply except for the cost differences. The changes in the cost difference do not affect the analysis of the barrier alternatives but the RAC(O) pavement with- out a barrier shows much lower NPVs by about $3,300,000 to $6,700,000. For the RAC(O) with no barrier, the predicted levels at 250 ft are equal to those of the HMA with an 8 ft bar- rier but less effective by 3 dB at 50 ft. After 9 years, the RAC(O) Pavement Type and Barrier Height Predicted Noise Level (dBA) N um be r o f B en ef ite d R ec ep to rs To ta l P ro jec t N PV ($0 00 ) NPV for Noise Abatement Relative to Ca ltr an s R ea so na bl en es s A llo w an ce ($ 00 0) W SD O T Re as on ab le ne ss A llo w an ce ($ 00 0) R ec ep to rs a t 17 5 ft R ec ep to rs a t 37 5 ft H M A B as el in e ($0 00 ) PC C Ba se lin e ($0 00 ) HMA + 8 ft 69 63 144 11,812 4,876 7,920 10,253 HMA + 12 ft 65 60 288 14,250 7,313 15,840 15,955 RAC(O) 72 63 144 8,539 1,603 7,920 10,253 RAC(O) + 8 ft 66 60 288 13,415 6,478 15,840 15,955 LT PCC + 8 ft 69 63 144 12,801 5,864 4,867 7,920 10,253 Ground PCC 74 65 0 9,273 2,337 1,339 0 0 Ground PCC + 8 ft 67 62 288 14,149 7,212 6,215 15,840 10,253 RT PCC + 12 ft 74 68 0 15,239 8,302 7,305 0 0 9-yr RAC(O) 75 66 0 8,539 1,603 0 0 9-yr RAC(O) + 8 ft 68 62 288 13,415 6,478 5,481 15,840 10,253 20-yr LT PCC + 8 ft 72 66 144 12,801 5,864 4,867 7,920 10,253 Table 11. Predicted noise levels with abatement, number of benefited receptors, NPV costs, and reasonable allowances for various abatement scenarios (receptors on both sides).
33 will become only 2 dB quieter than the HMA baseline with no abatement. However, there is no acoustic longevity in per- formance of the HMA as its acoustic performance is taken to be the same as TNM Average Pavement (i.e., 0 dB/year). Cal- trans Quieter Pavement Research work estimates an increase in the noise level for a dense-graded HMA of about 1 to 1.5 dB in a 9-year period (20). Even considering this increase, the RAC(O) alternative will not meet a 7 dB design goal and it will not meet feasibility and cost-reasonableness requirements at the end of the rehabilitation cycle. This example case illustrates the analysis that could be done using the methodology developed in this research. In these high-density alternatives and for these agency allowances, cost reasonableness is not an issue as long as there are some benefited receptors. Other iterations of barrier height, quieter pavement life cycle, policy criterion, reasonableness allowances, pavement type, acoustic longevity, etc., could alter the results significantly. Therefore, more appropriate results will be obtained if an agencyâs own data, practices, costs, etc. are used in the analysis. Example 2: Low-Density Case This example is patterned after an area along I-475 in Michigan in the Grand Blanc/Flint area. The residents are more widely spaced and set back further from the highway; the geometry of the site is shown in Figure 18. In this case, the den- sity of the receptors is low. The first row of 13 residential recep- tors is about 175 ft from the center of the near lane with 3 more at a distance of about 250 ft. The second row of 11 receptors is about 375 ft from the roadway. The pavements considered are the same as those used in the high-density case. This project extends only 1,690 ft for the length of a barrier that would shield these receptors. The levels and impacts for the three receptor distances are shown in Table 12 together with the NPV of each pavement alternative. The Michigan Department of Transportation (MDOT) uses a level of 66 dBA to identify impacted receptors (62) (similar to Caltrans and WSDOT). With this criterion none of the receptors at the 375 ft distance would be considered as impacted initially except if RT PCC were considered as the baseline pavement (Table 12). Similar to the previous example case, barrier heights of 8 and/or 12 ft were considered for noise abatement in com- bination with different pavement alternatives. The resulting noise levels are shown in Table 13 together with the barrier insertion losses (as appropriate) and the overall noise reduc- tion compared to either the HMA and LT PCC or the RT PCC (noise reductions for the HMA and LT PCC are the same regardless of pavement type, see Table 8). The MDOT policy uses the design goal of a 10 dB reduction for at least one ben- efited receptor and a 7 dB reduction for 75% of all benefited receptors. If the HMA or the LT PCC levels are considered as the baseline, none of the receptors realize this goal. However, with the RT PCC as a baseline, all options meet this criterion Pavement 13 Receptors at 175 ft 3 Receptors at 250 ft 11 Receptors at 375 ft Total Number of Impacts NPV Cost ($000) Level (dBA) Impacts Level (dBA) Impacts Level (dBA) Impacts HMA 70 13 67 3 63 0 16 2,220 RAC(O) 66 13 63 0 60 0 13 2,733 LT PCC 70 13 67 3 63 0 16 2,537 Ground PCC 68 13 65 0 61 0 13 2,968 RT PCC 76 13 73 3 68 11 27 2,537 9-yr RAC(O) 68 13 66 3 62 0 16 20-yr LT PCC 73 13 70 3 66 11 27 Table 12. Predicted traffic noise levels, number of impacted receptors, and NPV costs for Example 2. Barrier Source: Google Earth © 2011 Europa Technologies Figure 18. Aerial photograph of a portion of I-475 near Grand Blanc/Flint, Michigan, used as an example case for lower density receptors.
34 except the ground PCC pavement without a barrier. Although the design goals are not achieved, the analysis was carried through to completion. For feasibility, MDOT requires a 5 dB reduction for at least 75% of the impacted receptors. Relative to the HMA or LT PCC baseline, the RAC(O) without a bar- rier, ground PCC without a barrier, and RT PCC do not meet this criterion (or that for Caltrans and WSDOT). If the RT PCC is used as the baseline, all alternatives except the ground PCC without a barrier meet the MDOT design goal of a 10 dB reduction and all alternatives meet the WSDOT and Caltrans goal of a 7 dB reduction and the feasibility requirement. For the evaluation of cost reasonableness, MDOT uses a barrier cost of $45/ft2 and an allowance of $41,208 per ben- efited receptor (i.e., those who receive 5 dB or more reduc- tion). Table 14 shows the allowance, the number of benefited receptors, the reasonableness allowance, and the NPV for the Pavement Type and Barrier Height 175 ft Receptors 250 ft Receptors 375 ft Receptors N oi se L ev el (d BA ) B ar rie r I L (dB ) dB Noise Reduction Relative to: N oi se L ev el (d BA ) B ar rie r I L (dB ) dB Noise Reduction Relative to: N oi se L ev el (d BA ) B ar rie r I L (dB ) dB Noise Reduction Relative to: H M A /L T PC C [7 0 d BA ] R T PC C [7 6 d BA ] H M A /L T PC C [6 7 d BA ] R T PC C [7 3 d BA ] H M A /L T PC C [6 3 d BA ] R T PC C [6 8 d BA ] HMA + 8 ft 65 5 5 11 63 4 4 10 60 3 3 8 HMA + 12 ft 62 8 8 14 60 7 7 13 57 6 6 11 RAC(O) 66 n/a 4 10 63 n/a 4 10 60 n/a 3 8 RAC(O) + 8 ft 61 9 9 15 60 4 7 13 57 3 6 11 LT PCC + 12 ft 61 9 9 15 60 7 7 13 57 6 6 11 Ground PCC 68 n/a 2 8 65 n/a 2 8 61 n/a 2 7 Ground PCC + 8 ft 64 6 6 12 62 3 5 11 59 2 4 9 RT PCC + 12 ft 66 10 4 10 65 7 2 8 62 6 1 6 9-yr RAC(O) + 8 ft 64 7 6 12 62 5 5 11 59 3 4 9 20-yr LT PCC + 12 ft 64 6 6 12 62 5 5 11 60 3 3 8 Table 13. Traffic noise levels, barrier insertion loss, and overall system noise reduction for Example 2. Table 14. Predicted noise levels with abatement, number of benefited receptors, NPV costs, and reasonable allowances for abatement scenarios â Example 2 (receptors on one side). Pavement Type and Barrier Height Predicted Noise Level (dBA) N um be r o f B en ef ite d R ec ep to rs To ta l P ro jec t N PV ($ 00 0) NPV for Noise Abatement Relative to M D O T Re as on ab le ne ss A llo w an ce ($ 00 0) Ca ltr an s R ea so na bl en es s A llo w an ce ($ 00 0) W SD O T Re as on ab le ne ss A llo w an ce ($ 00 0) R ec ep to rs a t 17 5 ft R ec ep to rs a t 37 5 ft H M A B as el in e ($0 00 ) PC C Ba se lin e ($0 00 ) HMA + 8 ft 65 60 16 2,901 680 659 880 771 HMA + 12 ft 62 57 27 3,241 1,021 1,113 1,485 1,168 RAC(O) 66 60 0 2,733 513 0 0 0 RAC(O) + 8 ft 61 57 27 3,414 1,193 1,113 1,485 1,168 LT PCC + 12 ft 61 57 27 3,557 1,337 1,021 1,113 1,485 1,168 Ground PCC 68 61 0 2,968 748 431 0 0 0 Ground PCC + 8 ft 64 59 16 3,648 1,428 1,112 659 880 771 RT PCC + 12 ft 66 62 27 3,557 1,337 1,021 1,113 1,485 1,168 9-yr RAC(O) + 8 ft 64 59 16 3,414 1,193 659 880 771 20-yr LT PCC + 12 ft 66 60 16 3,557 1,337 1,021 659 880 771
35 project and the abatement strategy considering MDOT cri- teria (the allowances using Caltrans and WSDOT criteria are also shown). Of the alternatives that meet the feasible criteria, the HMA with an 8 ft barrier does not meet the MDOT design goal and thus is not reasonable (but it meets the goals of both Caltrans and WSDOT). Relative to the PCC NPV baseline, the LT PCC with a 12 ft barrier is reasonable according to the criteria for the three agencies. The ground PCC with an 8 ft (or increased height) barrier is not reasonable by any of the agenciesâ criteria. The RT PCC with a 12 ft barrier is reason- able for all agencies only if the baseline pavement is RT PCC. The assessment of the feasibility, cost reasonableness, and achievement of design goals of the pavementâbarrier alter- natives is summarized in Table 15. Effectiveness is shown as the difference between the lowest absolute level for any of the options and the level for a specific option. The additional cost relative to the lowest cost option is also shown. The HMA, LT PCC, or RT PCC all with 12 ft barriers would meet the MDOT criteria but not the design goal. Of these alternatives with 12 ft barriers, the LT PCC pavement is most effective in providing the lower levels, but the HMA alternative is only 1 dB higher and only at the 175 ft receptor distance. The RT PCC alterna- tive is less effective than the LT PCC even though the NPV is the same. Of the HMA and LT PCC with 12 ft barriers, the HMA has the overall lowest NPV by $316,000. Using the Cal- trans allowances, RAC(O) with an 8 ft barrier would also be cost reasonable (in addition to the HMA and LT PCC with 12 ft barriers alternatives). The levels for the RAC(O) with an 8 ft barrier are similar to the HMA and LT PCC with 12 ft barriers with the total cost in between these two. The selection from among the RAC(O) with an 8 ft barrier, the HMA with a 12 ft barrier, and the LT PCC with a 12 ft barrier when con- sidering Caltrans criteria may be determined by other consid- erations such as cost, preferred pavement type, and user costs. Example 3: Two-Barrier Case This example is for a six-lane new highway construction developed around the geometry shown in Figure 19 along I-93 near the Town of Medford, Massachusetts, north of Table 15. Assessment of alternatives under MDOT, Caltrans, and WSDOT policies for Example 2. Pavement Type and Barrier Height MDOT Caltrans WSDOT Ef fe ct iv en es s ( dB ) Cost Difference ($000) Relative to Fe as ib le Co st Re as on ab le D es ig n G oa l Fe as ib le Co st Re as on ab le D es ig n G oa l Fe as ib le Co st Re as on ab le D es ig n G oa l H M A PC C HMA + 8 ft Y N N Y Y N Y Y N 4 167 HMA + 12 ft Y Y N Y Y Y Y Y Y 1 508 RAC(O) N N N N N N 5 0 RAC(O) + 8 ft Y N N Y Y Y Y N Y 0 680 LT PCC + 12 ft Y Y2 N Y Y Y Y Y2 Y 0 824 589 Ground PCC N N N N N N 7 235 0 Ground PCC + 8 ft Y N N Y N N Y N N 3 915 680 RT PCC + 12 ft Y1 Y2 Y1 Y1 Y Y1 Y1 Y Y1 5 824 589 9-yr RAC(O) + 8 ft Y N N Y N N Y N N 3 680 20-yr LT PCC + 12 ft Y N N Y N N Y N N 5 824 589 1 Relative to RT PCC baseline only, not for HMA or LT PCC 2 Relative to PCC cost only, not for HMA cost Barriers Figure 19. Aerial photograph of a portion of I-93 near Medford, Massachusetts, with receptors and proposed barriers on both sides of a highway.
36 Boston. In this case, receptors with about the same density are located on both sides of the highway. The project area is from Webster Street to Valley Street for a length of about 1,140 ft. There are 47 receptors along the project area. On the south- bound side, there are 30 receptors (the sum of those located approximately 100 ft, 175 ft, and 250 ft from the near lane of travel). On the northbound side, a total of 17 receptors are distributed over these same three distances. Tables 16 and 17 provide the predicted noise levels and impacts for the south- bound and northbound sides, respectively. The Massachusetts Department of Transportation (MassDOT) defines an impact as when the noise levels are within 1 dB of the FHWA NAC (66 dBA) (63)âthe same criteria used by WSDOT, Caltrans, and MDOTâresulting in the same number of impacted recep- tors. For both the RAC(O) and ground PCC pavements, the levels are below 66 dBA at 250 ft, which reduces the number of impacted receptors. Tables 16 and 17 also provide the NPV costs for each pave- ment type. For this example case, the pavement NPVs apply to both the northbound and southbound directions, but the barrier NPVs apply to each side individually and are analyzed separately. MassDOT considers acoustic feasibility to be achieved when more than 50% of the first row receptors receive a 5 dB reduc- tion. The design goal of 10 dB is met when at least one receptor in the first row receives this reduction. For cost reasonable- ness, MassDOT uses an index calculation procedure that is not directly compatible with the LCCA methodology developed in this research. The cost-effectiveness index used by MassDOT is the cost of the barrier based on $50/ft2 divided by the aver- age insertion loss divided by the number of benefited recep- tors that receive a 5 dB or more reduction. In these cases, a cost allowance could not be determined, but the MassDOT-type barrier cost was used in the LCCA to determine whether the barrier met the cost-effectiveness index. The barrier heights considered in the analysis ranged from 8 to 12 ft depending on the pavement. Cost allowances were also calculated using MDOT and WSDOT methods. The predicted levels, barrier insertion losses, and pavementâ barrier noise reductions are shown in Table 18 for the differ- ent receptor distances and pavement baselines. As in the previ- ous example, the HMA and LT PCC baselines were considered together because of their similar levels at most receptor loca- tions and the RT PCC was considered as an additional base- line. The data in Table 18 applies to both the southbound Pavement 7 Receptors at 100 ft 2 Receptors at 175 ft 8 Receptors at 250 ft Total Number of Impacts NPV Cost ($000) Level (dBA) Impacts Level (dBA) Impacts Level (dBA) Impacts HMA 74 7 70 2 67 8 17 1,498 RAC(O) 69 7 66 2 63 0 9 1,844 LT PCC 73 7 70 2 67 8 17 1,711 Ground PCC 71 7 68 2 65 0 9 2,002 RT PCC 79 7 76 2 73 8 17 1,711 9-yr RAC(O) 72 7 68 2 66 8 17 20-yr LT PCC 76 7 73 2 70 8 17 Table 17. Predicted traffic noise levels, number of impacted receptors, and NPV costs for Example 3 (northbound side). Pavement 14 Receptors at 100 ft 6 Receptors at 175 ft 10 Receptors at 250 ft Total Number of Impacts NPV Cost ($000) Level (dBA) Impacts Level (dBA) Impacts Level (dBA) Impacts HMA 74 14 70 30 67 10 1,498 RAC(O) 69 14 66 20 63 0 1,844 LT PCC 73 14 70 6 67 10 30 1,711 Ground PCC 71 14 68 6 65 0 20 2,002 RT PCC 79 14 76 6 73 10 30 1,711 9-yr RAC(O) 72 14 68 6 66 10 30 20-yr LT PCC 76 14 73 6 70 10 30 Table 16. Predicted traffic noise levels, number of impacted receptors, and NPV costs for Example 3 (southbound side).
37 and northbound sides of the highway as the results are inde- pendent of the number of receptors. For the HMA/LT PCC baseline, only the HMA with 12 ft barriers, the RAC(O) with 8 ft barriers, and the LT PCC with 12 ft barriers meet the MassDOT (and MDOT) design goal. Relative to RT PCC, all alternatives except the ground PCC meet the 10 dB design goal. In terms of acoustic feasibility, all alternatives except ground PCC meet the criterion relative to both the HMA/LT PCC and the RT PCC baselines. The LCCA NPVs for the two sides of the highway are the same because the pavement and barrier lengths are the same; results are presented in Table 19. The allowances based on MDOT and WSDOT criteria for the southbound and north- bound sides are different due to the difference in the number Pavement Type and Barrier Height 100 ft Receptors 175 ft Receptors 250 ft Receptors N oi se L ev el (d BA ) B ar rie r I L (dB ) dB Noise Reduction Relative to: N oi se L ev el (d BA ) B ar rie r I L (dB ) dB Noise Reduction Relative to: N oi se L ev el (d BA ) B ar rie r I L (dB ) dB Noise Reduction Relative to: H M A /L T PC C [7 4 d BA ] R T PC C [7 9 d BA ] H M A /L T PC C [7 0 d BA ] R T PC C [7 6 d BA ] H M A /L T PC C [6 7 d BA ] R T PC C [7 3 d BA ] HMA + 10 ft 66 8 8 13 64 6 6 12 63 4 4 4 HMA + 12 ft 64 10 10 15 62 8 8 14 60 7 7 7 RAC(O) 69 n/a 5 10 66 n/a 4 10 63 n/a 4 4 RAC(O) + 8 ft 64 5 10 15 61 4 9 15 60 3 7 7 LT PCC + 12 ft 63 10 11 16 61 9 9 15 60 7 7 7 Ground PCC 71 n/a 3 8 68 n/a 2 8 65 n/a 2 2 Ground PCC + 8 ft 66 6 8 13 64 4 6 12 62 4 5 5 RT PCC + 12 ft 68 11 6 11 66 10 4 10 65 8 2 2 9-yr RAC(O) + 8 ft 66 6 8 13 64 5 6 12 62 4 5 5 20-yr LT PCC + 12 ft 65 11 9 14 63 9 7 13 62 8 5 5 Table 18. Traffic noise levels, barrier insertion loss, and overall system noise reduction for receptors for Example 3 (both sides). Pavement Type and Barrier Heights To ta l P ro jec t N PV ($ 00 0) NPV for Noise Abatement Relative to Southbound Side Northbound Side H M A B as el in e ($0 00 ) PC C Ba se lin e ($0 00 ) N um be r o f B en ef ite d R ec ep to rs M D O T Re as on ab le ne ss A llo w an ce ($ 00 0) W SD O T Re as on ab le ne ss A llo w an ce ($ 00 0) N um be r o f B en ef ite d R ec ep to rs M D O T Re as on ab le ne ss A llo w an ce ($ 00 0) W SD O T Re as on ab le ne ss A llo w an ce ($ 00 0) HMA + 10 ft 2,135 637 20 824 899 9 371 449 HMA + 12 ft 2,263 765 30 1,236 1,596 17 701 867 RAC(O) 1,844 346 14 577 1,200 7 288 550 RAC(O) + 8 ft 2,354 856 30 1,236 1,596 17 701 867 LT PCC + 12 ft 2,476 978 765 30 1,236 1,596 17 701 867 Ground PCC 2,002 504 291 0 0 0 0 0 0 Ground PCC + 8 ft 2,512 1,014 801 30 1,236 1,596 17 701 867 RT PCC + 12 ft 2,476 978 765 301 1,236 1,596 171 701 867 9-yr RAC(O) + 8 ft 2,354 856 643 30 1,236 1,596 17 701 867 20-yr LT PCC + 12 ft 2,476 978 765 30 1,236 1,596 17 701 867 1 Relative to RT PCC baseline only, not for HMA or LT PCC Table 19. Total project and abatement NPV, number of benefited receptors, and reasonableness allowances for Example 3 (both sides).
38 of benefited receptors. For the southbound side, all alternatives except ground PCC without a barrier provided sufficient allow- ances to be cost reasonable for both MDOT and WSDOT cri- teria. None of the alternatives for the northbound side (with the fewer number of benefited receptors) are cost reasonable using the MDOT allowances. Using WSDOT criteria, only the HMA with 10 ft barriers is not cost reasonable. However, the PCC alternatives are only cost reasonable when a PCC pavement NPV cost is used. The summary provided in Table 20 shows if an alternative meets acoustic feasibility requirements, cost-reasonableness requirements, and the design goals for the southbound side when considering the MassDOT, MDOT, and WSDOT cri- teria. The MassDOT cost-effectiveness index was calculated for each alternative, except for the RAC(O) and ground PCC without barriers. A review of the cost-reasonableness data shows that all alternatives except ground PCC with- out barriers meet the three agenciesâ criteria but the RT PCC with 12 ft barriers only meets the criteria when the noise reduction is compared to the RT PCC without bar- riers. Similar results were obtained for feasibility with the ground PCC without barriers being the only alternative that did not meet the criteria. The RAC(O) without barriers did not achieve the 5 dB threshold when applied to 75% of the impacted receptors (MDOT criteria). Considering effec- tiveness and cost difference, the HMA with 12 ft barriers, the RAC(O) with 8 ft barriers, and the LT PCC with 12 ft barriers were nearly equal to the HMA baseline but have a slight cost advantage. As all alternatives met the feasible and reasonable criteria, other criteria will be used to select the preferred alternative. Because of the smaller number of impacted and benefited receptors, the cost-reasonableness considerations for the north- bound side are somewhat different from that for the south- bound side; a summary of the results is given in Table 21. Under the MDOT criteria, none of the alternatives are cost reasonable, but the HMA with 12 ft barriers, the RAC(O) with 8 ft barri- ers, and the LT PCC with 12 ft barriers meet the feasibility and cost-reasonableness criteria under the MassDOT and WSDOT criteria. This example case illustrates another feature in noise abate- ment analysis when quieter pavements are used. If the RAC(O) with 8 ft barriers was selected for the southbound side, it would benefit seven more receptors on the northbound side even with- out the barrier on that side because of the quieter pavement. Therefore, when considering MDOT criteria, the combined alternative of RAC(O) with an 8 ft barrier on the southbound and no barrier on the northbound side would become cost rea- sonable for both sides with some amount of noise reduction provided to the impacted receptors on the northbound side. Also, this combined alternative would be acoustically feasible and meet the goal of one receptor receiving a 10 dB reduction and 75% of the receptors receiving 7 dB reductions. When con- sidering the other statesâ criteria, this combined alternative also may have merit because the RAC(O) without a barrier was also an acoustically feasible alternative. This combined alternative would provide cost savings of about $510,000 to $730,000 com- pared to the alternatives with barriers on both sides. Pavement Type and Barrier Height MassDOT MDOT WSDOT Ef fe ct iv en es s ( dB ) Cost Difference ($000) Relative to Fe as ib le Co st Re as on ab le D es ig n G oa l Fe as ib le Co st Re as on ab le D es ig n G oa l Fe as ib le Co st Re as on ab le D es ig n G oa l H M A PC C HMA + 10 ft Y Y N Y Y N Y Y Y 3 291 HMA + 12 ft Y Y Y Y Y Y Y Y Y 1 419 RAC(O) Y N N Y N Y Y N 6 0 RAC(O) + 8 ft Y Y Y Y Y Y Y Y Y 1 510 LT PCC 12 ft Y Y Y Y Y Y Y Y Y 0 632 474 Ground PCC N N N N N N N N 8 158 0 Ground PCC + 8 ft Y Y N Y Y N Y Y Y 3 668 510 RT PCC + 12 ft Y1 Y1 Y1 Y1 Y Y1 Y1 Y Y1 5 632 474 9-yr RAC(O) + 8 ft Y Y N Y Y N Y Y Y 3 510 20-yr LT PCC + 12 ft Y Y N Y Y N Y Y Y 2 632 474 1 Relative to RT PCC baseline only, not for HMA or LT PCC Table 20. Assessment of alternatives under different criteria for Example 3 (southbound side).
39 Summary and Discussion The preceding examples illustrated the applicability of the methodology for evaluating noise abatement alterna- tives using barriers, quieter pavement, and combinations of both. It showed that acoustic feasibility for alternatives could be evaluated in a similar manner to that currently used for barriers alone. For reasonableness, the methodology could be applied con- sidering existing or modified agency criteria. For example, con- sideration may be given to lowering design goals to the levels achievable by quieter pavement. The concept of effectiveness based on the differences in absolute level from the quietest to noisiest alternatives was also useful in comparing alternatives when considering the economic features and the NPV of the alternatives. Also, acoustic longevity could be included in the analysis with the use of OBSI data as a performance measure at the end of the rehabilitation cycle (or other established appro- priate time). Although the specific cases presented in this chapter dem- onstrate that the methodology can be used within the con- text of existing policies, some cases (e.g., use of two barriers) require special attention. In evaluating noise abatement for barriers, currently, each case is considered individually even on two sides of a single pavement section. If receptors on both sides are impacted, it would be appropriate to evaluate them together, particularly when quieter pavement or combinations of barriers and pavement are considered. Pavement Type and Barrier Height MassDOT MDOT WSDOT Ef fe ct iv en es s ( dB ) Cost Difference ($000) Relative to Fe as ib le Co st Re as on ab le D es ig n G oa l Fe as ib le Co st Re as on ab le D es ig n G oa l Fe as ib le Co st Re as on ab le D es ig n G oa l H M A PC C HMA + 10 ft Y N N Y N N Y N Y 3 291 HMA + 12 ft Y Y Y Y N Y Y Y Y 1 419 RAC(O) Y N N N N Y Y N 6 0 RAC(O) + 8 ft Y Y Y Y N Y Y Y Y 1 510 LT PCC + 12 ft Y Y Y Y N Y Y Y2 Y 0 632 474 Ground PCC N N N N N N N N 8 158 0 Ground PCC + 8 ft Y Y N Y N N Y Y2 Y 3 668 510 RT PCC + 12 ft Y1 Y1 Y1 Y1 N Y1 Y1 Y2 Y1 5 632 474 9-yr RAC(O) + 8 ft Y Y N Y N N Y Y Y 3 510 20-yr LT PCC + 12 ft Y Y N Y N N Y Y Y 2 632 474 1 Relative to RT PCC baseline only, not for HMA or LT PCC 2 Relative to PCC cost only, not for HMA cost Table 21. Assessment of alternatives under MassDOT, MDOT, and WSDOT policies for Example 3 (northbound side).
