Traffic Noise and Vibration Impact Assessment Technical Report for the North Meadows Extension to US 85 and Interstate 25

Transcription

1 Traffic Noise and Vibration Impact Assessment Technical Report for the North Meadows Extension to US 85 and Interstate 25 February 2010 Prepared for: Town of Castle Rock Douglas County Colorado Department of Transportation Federal Highway Administration Prepared by: Dale Tischmak, Senior Environmental Scientist Felsburg Holt & Ullevig 6300 S. Syracuse Way, Suite 600 Centennial, CO (303) FHU Reference No

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3 TABLE OF CONTENTS Page 1.0 INTRODUCTION Project Description Basics of Sound Basics of Vibration Noise Analysis Approach ANALYSIS METHODS Traffic Noise Measurement Traffic Noise Modeling Methods AFFECTED ENVIRONMENT Previous Studies Traffic Noise Measurements Traffic Noise Verification Model Traffic Noise Model Results ENVIRONMENTAL CONSEQUENCES No-Build Alternative 2030 Results Refined Alternative Results Refined Alternative Results Summary of Traffic Noise Impacts Construction Noise MITIGATION EVALUATION Existing Noise Barriers Evaluation of Mitigation Other than Barriers Assessment of Nonproject Impacts Traffic Noise Barrier Evaluations Summary of Recommended Mitigation Impacted Receivers After Recommended Mitigation REFERENCES Page i

4 LIST OF FIGURES Page Figure 1 Study Area Figure 2 Build Alternatives Analyzed for Noise Impacts Figure 3 Typical Sound Levels Figure 4 Adjustments to Sound Levels by Sound Frequency for A-Weighting Figure 5 Traffic Noise Measurement Locations and Existing Sound Levels Figure 6 Traffic Noise Model Receiver Locations Figure 7 Existing Berms in Study Area Figure 8 Impacted Receivers from Existing Conditions Noise Model Figure 9 Noise Impacted Areas for No-Build Alternative-Year Figure 10 Noise Impacted Areas for Refined Alternative 6 (Year 2030) Figure 11 Noise Impacted Areas for Refined Alternative 7 (Year 2030) Figure 12 Locations of Traffic Noise Mitigation Barriers Evaluated Figure 13 Traffic Noise Impacts After Recommended Mitigation Actions LIST OF TABLES Table 1 CDOT Noise Abatement Criteria Table 2 Existing Traffic Noise Measurement Results Table 3 Verification Noise Model Results Table 4 Summary of Receivers Impacted by Traffic Noise Table 5 Traffic Noise Mitigation Barrier Summary APPENDIX APPENDIX A Noise Measurement Data APPENDIX B Noise Model Receivers and Results APPENDIX C Traffic Noise Mitigation Barriers APPENDIX D Barrier Evaluation Forms Page ii

5 1.0 INTRODUCTION The National Environmental Policy Act (NEPA) of 1969 established a mandate for federal agencies to consider the potential environmental consequences of their proposed actions, to document the analysis, and to make the information available to the public for comment prior to implementation. In accordance with NEPA and related regulations, the Federal Highway Administration (FHWA), as the Lead Agency, in cooperation with the Colorado Department of Transportation (CDOT) as a Joint Lead Agency, has prepared this (EA) for a proposed extension of North Meadows Drive from The Meadows area to US Highway 85 (US 85) and to Interstate 25 (I-25) in Douglas County, Colorado. The proposed North Meadows Extension would cross the Burlington Northern Santa Fe (BNSF) Railway, East Plum Creek, and the Union Pacific Railroad (UPRR) (Figure 1 Study Area). The project is sponsored by the Town of Castle Rock and Douglas County. The US Department of the Interior Fish and Wildlife Service (USFWS) is a Cooperating Agency. The purpose of the analyses presented in this report is to conclude whether noise or vibration levels at the properties (i.e., receivers) near the potential road improvements from the project alternatives may exceed applicable thresholds, according to CDOT or FHWA guidelines. This report presents an overall analysis that was performed as part of the EA to evaluate existing and future traffic noise levels as well as assess potential impacts to properties near the road improvements from noise and vibration from road traffic. Train noise will not be changed by the proposed improvements and was not part of the analysis. 1.1 Project Description The study area has residences, businesses, schools and undeveloped areas abutting the streets and roads of interest for the project. The study area includes several developing areas, so more homes and businesses are expected in the area in the future. Residential areas are typically the land use most sensitive to noise or vibration impacts (Section 2.0 Analysis Methods) and there are many residences close to roads examined for the project (Section 3.4 Traffic Noise Model Results). Other sensitive land uses include parks, schools, some types of businesses, and hospitals. The locations normally examined for noise are occupied exterior (ground level) spaces while those examined for vibration would be any buildings or interior spaces. Two future build alternatives, and the No-Build Alternative, are being considered in the traffic noise analysis, and each alternative was examined for potential noise or vibration impacts. The No-Build Alternative has no new road improvements as part of this project, though changes to the road network may be made by other projects. The two build alternatives evaluated in this report would each establish a new 4-lane roadway connection between I-25 and Meadows Boulevard. Refined Alternatives 6 and 7 each consist of different sets of road improvements within the study area. Both would extend and widen North Meadows Drive to the Burlington Northern Santa Fe Railway, but from there the alternatives follow one of two different routes across US 85 to connect with one location at I-25 (Figure 2 Build Alternatives Analyzed for Noise Impacts). For additional details on the road improvements, see the EA document. Page 1

6 Figure 1 Study Area Source: Felsburg Holt & Ullevig (FHU) project data, Page 2

7 Figure 2 Build Alternatives Analyzed for Noise Impacts Source: FHU project data, Page 3

8 1.2 Basics of Sound Sound is created when an object vibrates and radiates part of that energy as acoustic pressure or waves through a medium, such as air, water or a solid. Noise is commonly defined as unwanted sound. Sound and noise have many characteristics that are important to consider for impacts, including loudness (energy intensity), frequency, and fluctuations over time. Sound and noise intensities are measured in units of decibels (db). The db scale is logarithmic, not linear. To illustrate this, consider that two identical noise sources, each producing 60 db, would produce 63 db when added together. Likewise, a 10-dB increase in sound levels represents ten times more sound energy. The human ear can accommodate a wide range of sound energy levels, with the maximum levels having more than a million times the sound energy of the minimum levels. Examples of common sound levels are shown in Figure 3 Typical Sound Levels. Figure 3 Typical Sound Levels Source: FTA, 2006 The human ear is not equally receptive to all frequencies of sound-producing vibrations. Mathematical adjustments to sound levels by sound frequencies using the A weighting network are often used to approximate how the human ear perceives a sound, mostly by reducing the contributions from low and extremely high sound frequencies by a specified amount (Figure 4 Adjustments to Sound Levels by Sound Frequency for A-Weighting). Sound levels that have been weighted this way are reported in dba. Research has shown that most people do not notice a difference in loudness between sound levels of less than 3 dba, which is a two-fold change in the sound energy. Most people relate a 10-dBA increase in sound levels to a doubling of sound loudness. Page 4

9 Noise often fluctuates over time because of the characteristics of the source. Traffic noise will fluctuate from changes in traffic volumes, vehicle types, and vehicle speeds. This fluctuation makes it difficult to describe noise adequately through a single value, but FHWA and CDOT use the one-hour equivalent sound level (L eq ) as the metric for assessing traffic noise impacts. In simple terms, the L eq is the average of the fluctuating noise levels over a time period, or more precisely, the constant noise level that would produce the same amount of sound energy overall as the fluctuating noise level. Figure 4 Adjustments to Sound Levels by Sound Frequency for A-Weighting Sound Level Adjustment (db) Source: FTA, 2006 Sound levels decrease with distance from the source because of spreading, atmospheric absorption, interference from objects and ground effects. "Hard" ground (such as asphalt) and "soft" ground (such as grass) affect sound transmission differently. Hard ground is more reflective and will produce louder sound levels farther from the source. Using traffic noise passing over hard ground as an example, either doubling the traffic volume or cutting the distance from the listener to the roadway in half could cause a 3-dBA increase in noise levels, which would be barely noticeable to most people. On busy roads and highways, the loudest traffic noise generally occurs when the largest traffic volume can travel at the highest speed, which is not necessarily rush hour when the traffic volume can be so high that roads become congested and speeds slow. This noisiest traffic condition generally corresponds to Level of Service (LOS) C for a highway. Page 5

10 1.3 Basics of Vibration Ground-borne vibration is the oscillatory motion of the ground about some equilibrium position, and can be described in terms either of displacement, velocity or acceleration. Because human sensitivity to vibration typically corresponds best to the amplitude of vibration velocity within the low frequency range of most concern (approximately Hertz), vibration velocity is the preferred measure for evaluating ground-borne vibration from transportation projects. There are no federal or state requirements directed specifically to traffic-induced vibration. Studies that have been done to assess the impact of traffic vibrations have shown that both measured and predicted traffic vibration levels are less than any known criteria for causing structural damage to buildings (FHWA, 1995). Often, normal indoor activities like closing doors have been shown to create greater levels of vibration in homes than nearby highway traffic. Because of these findings, vibration from road traffic is not a concern within the EA and will not be examined further in this analysis. Vibration from road construction could be a concern, if high-vibration construction techniques such as pile driving or blasting are used. Issues with construction-generated vibrations would depend on high-vibration activities occurring close to vibration-sensitive locations (Section 1.1 Project Description). At present, it is not expected that these types of construction techniques would be necessary and occur near sensitive properties, given the physical characteristics of the project area. If such construction techniques are necessary at a specific location, the vibration concerns will be addressed during construction planning on a case-by-case basis and appropriate mitigation action taken for the specific situation. Therefore, vibration from road construction will not be examined further in this analysis. 1.4 Noise Analysis Approach The overall purpose of the following noise analysis is to conclude whether noise levels at any receivers within 500 feet of potential project improvements may exceed applicable impact thresholds from the project alternatives. If so, mitigation actions for the impacted receivers would be considered for the project design. The analyses examined roads that would be changed or newly built by the project or would have substantially different traffic volumes because of an alternative. The overall analysis was based on measurements of existing conditions and on modeling of both existing (2007) conditions and future design year (2030) conditions (Section 2.0 Analysis Methods). Current conditions and the three future alternatives being considered in the analysis were examined. Currently, there are residences, schools and businesses near potential project roads, which are the most sensitive receivers to noise. Several measurements of existing noise were performed in the project area in 2007 (Section 3.0 Affected Environment). Computer modeling was used to examine existing and expected future conditions for numerous locations in the project area, focusing on potential impacts to the most sensitive receivers (Section 3.0 Affected Environment and Section 4.0 Environmental Consequences). The resulting noise levels were compared to applicable criteria to assess for and identify impacted areas (Section 4.0 Environmental Consequences). The efficacy of various mitigation measures for the impacted areas were evaluated and select mitigation measures were recommended, if appropriate according to FHWA and CDOT feasibility and reasonableness guidelines (Section 5.0 Mitigation Evaluation). Page 6

11 2.0 ANALYSIS METHODS Noise impacts from automobile traffic were evaluated through a combination of measurements and computer modeling. The specific methods used for each part of the analysis are described below. Because the roads of interest in the study area include state and federal highways, the appropriate noise impact criteria are the state and federal highway noise guidelines. CDOT has the most restrictive requirements of this group. Therefore, traffic noise impacts are assessed by comparing the traffic noise levels to the relevant CDOT Noise Abatement Criteria (NAC) (Table 1 CDOT Noise Abatement Criteria). For further comparison, typical noise levels are shown in Figure 3 Typical Sound Levels. The CDOT NAC for residences and other Category B properties is an exterior L eq of 66 dba, and the NAC for commercial areas (Category C) is an exterior L eq of 71 dba. Under CDOT guidelines, equaling or exceeding the NAC is viewed as a noise impact and triggers an investigation of noise mitigation measures (Section 5.0 Mitigation Evaluation). A substantial noise increase is also a noise impact and leads to evaluation of traffic noise mitigation actions. A substantial noise increase is defined as the future noise level increasing by 10 dba or more over existing levels. Table 1 CDOT Noise Abatement Criteria Land Use Category CDOT NAC (L eq ) Description of Land Use Category A 56 dba (Exterior) Tracts of land in which serenity and quiet are of extraordinary significance and serve an important public need and where the preservation of those qualities is to continue to serve its intended purpose. Such areas could include amphitheaters, particular parks, or open spaces which are recognized by appropriate local officials for activities requiring special qualities of serenity and quiet. B 66 dba (Exterior) Residences, motels, hotels, public meeting rooms, schools, churches, libraries, hospitals, picnic areas, playgrounds, active sports areas, and parks. C 71 dba (Exterior) Developed lands, properties or activities not included in categories A and B above. D None Undeveloped lands. E 51 dba (Interior) Residences, motels, public meeting rooms, schools, churches, libraries, hospitals, and auditoriums. Source: CDOT, 2002 For the noise impact discussion, the peak hour refers to the highest traffic noise hour, which may or may not correspond to the hour of largest traffic volume. Traffic noise can decrease during rush hour due to lower vehicle speeds from overloaded and congested roads. Page 7

12 2.1 Traffic Noise Measurement The traffic noise measurements were taken with a Svantek 945A Type 1 sound level meter calibrated at the site with a Norsonic 1251 calibrator. This equipment conforms to American National Standards Institute Standard S1.4 for Type 1 sound level meters. Calibrations traceable to the U.S. National Institute of Standards and Technology were performed in the field before and after each set of measurements using the acoustical calibrator. The measurement microphone was protected by a windscreen and located on a tripod approximately 5 feet above the ground. The microphone was positioned at each site to characterize the exposure to the dominant noise sources in the area. Noise measurements were made during weather conditions, including wind speed, that were acceptable according to FHWA guidance (FHWA, 1996) and weather conditions were monitored during the measurements. The traffic noise measurements were spread over a variety of locations in the study area. Short-term (10-minute) traffic noise measurements were performed in duplicate back to back in the afternoon at a number of locations (Section 3.2 Traffic Noise Measurements) to document existing ambient conditions in the study area. Traffic counts, including the number of large trucks, were collected when possible during the noise measurement periods (Appendix A); however, clear views of traffic were not always available from the measurement site. The measurement results were used to document ambient conditions and to evaluate the performance of the computer models. 2.2 Traffic Noise Modeling Methods Three future alternatives are being evaluated through this analysis one no-build alternative and two build alternatives. Each build alternative may include new interchanges (I-25 or US 85), new roads, or realigned/widened roads. Other changes, such as increased traffic volumes or increased traffic speeds, may lead to noise impacts from traffic. The build alternatives (Refined Alternatives 6 and 7) would add an interchange to I-25, so it is important to consider I-25 traffic. The other important noise sources that are the focus of the traffic noise modeling include US 85 and the current/future arterial streets. Computer modeling was performed for both current conditions and the three project alternatives for Year Modeling is used because day-to-day variations in traffic or weather conditions that affect noise levels cannot be captured or quantified by brief noise measurements alone, and because the future noise levels can not be measured now. In addition, the modeling can evaluate many more locations than can reasonably be field measured. The modeling results represent predicted typical average traffic conditions during peak noise periods. The traffic noise modeling software is FHWA s Traffic Noise Model (TNM) Version 2.5. The ultimate purpose of the models is to examine whether traffic noise levels would be high enough to impact neighboring properties, and subsequently whether noise mitigation should be provided for any such impacts within the study area. The existing traffic conditions model included the 2007 road configurations and traffic volumes. The three alternatives were modeled for their respective 2030 conditions (Section 1.1 Project Description). Often, LOS C traffic conditions (1,600 vehicles per lane per hour) are modeled for I-25 because 2030 peak traffic volumes are often predicted to exceed LOS C capacities. The conditions examined for the other highways and arterial roads use the predicted afternoon peak traffic volumes, except for North Meadows Drive (near Castle View High School) where the peak morning traffic is used because it is predicted to be higher than the afternoon peak. Page 8

13 TNM was used to calculate noise levels at more than 300 points up to 500 feet from a modeled roadway. This distance follows CDOT guidance (CDOT, 2002) and was identified as being sufficient to identify the receivers that could be impacted by the alternatives. In some cases, a single model point represents several nearby receivers/properties where traffic and geography were similar (e.g., one point for a multi-unit apartment building), so the number of model points is not always the same as the number of individual receivers. The modeled roadways are the roads that would be built or changed by the build alternatives or are important local noise sources. The same model points are used in each model for consistency (Appendix B), unless a specific alternative removes a specific receiver. The TNM models require a considerable amount of input data regarding the geometry of the roadways as well as traffic volumes, vehicle mix and vehicle speeds. Detailed traffic studies were completed for the project (FHU, 2008) to provide traffic volumes. The current positions of roads and streets were mapped and used in both the existing and No-Build Alternative models, though individual road parameters differed between the two models. Refined Alternatives 6 and 7 (Section 1.1 Project Description) were modeled to assess the possible noise impacts from the proposed roadway additions and changes. In general, the following data were used in the models: Units feet and miles per hour Current Roadway Alignments XY coordinates from CAD files and aerial photographs Future Roadway Alignments XY coordinates from CAD files Vehicle Speeds ranged from miles per hour (MPH), depending on road Traffic Volumes from traffic study (LOS C volumes for I-25 when needed, peak hour for others) Vehicle Mix from noise measurement vehicle count data and CDOT traffic count data Elevations from ground surface contours of the study area and preliminary road designs; model points were 5 feet above ground Structural and terrain barriers were used as needed to emulate the existing area; mitigation barriers were added to models where appropriate for the mitigation evaluations. Several traffic noise barriers have been built in the area and these were included in the models. Page 9

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15 3.0 AFFECTED ENVIRONMENT The current traffic noise conditions in the study area were assessed through a combination of measurements and modeling. There are several residential and business areas within the study area that are of interest to the project. The existing conditions for traffic noise for these areas are presented below. 3.1 Previous Studies A traffic noise study was completed previously for much of the study area by the South I-25 Corridor and US 85 Corridor Final Environmental Impact Statement (EIS) project (CDOT, 2001). Of importance for the EA traffic noise analysis, the EIS identified some impacted receivers within the current study area and recommended one noise mitigation berm along I-25 for the Happy Canyon neighborhood. A berm has since been built. The EIS study differs from the current study for a couple of key reasons: the EIS examined a different design year (2020), so future traffic volumes were lower the EIS examined fewer receivers (some buildings were not yet built) the EIS did not examine any new interchanges in the study area the EIS used different modeling software (STAMINA), as required at that time For these reasons, there are differences in results between the EA noise study and the EIS analyses. 3.2 Traffic Noise Measurements The short-term noise measurements described below were intended to be representative of daily peak traffic noise periods. Short-term traffic noise measurements were performed in the afternoon in the project area to document existing ambient conditions (Table 2 Existing Traffic Noise Measurement Results). These locations (Figure 5 Traffic Noise Measurement Locations and Existing Sound Levels) include residential, commercial and undeveloped areas along the project corridors that are under consideration for the EA. Each location is also representative of other nearby properties that may have the same or different land uses. Table 2 Location Number Existing Traffic Noise Measurement Results Location Description Land Use CDOT NAC Category* (dba)* block North Meadows Drive B block Castlegate Drive West D None block US 85 D None block Allen Street B block North Meadows Drive B block Meadows Boulevard D None block Castlegate Drive North B block Canyon Lane B * See Table 1. Source: FHU field data, Measured L eq (dba) Page 11

16 Figure 5 Traffic Noise Measurement Locations and Existing Sound Levels Source: FHU field data, Page 12

17 None of the measurement results exceed the applicable CDOT NAC for the locations in the project area (Table 2 Existing Traffic Noise Measurement Results). These include properties along I-25 protected by existing berms (Section 3.4 Traffic Noise Model Results). However, some of the results are near the NAC, so noise levels at other times or nearby locations may reach the relevant NAC. 3.3 Traffic Noise Verification Model As a check on noise model parameters, the traffic conditions observed during the noise measurements were used to construct a verification model in TNM. The intent is to check the accuracy of the noise levels calculated through a model that reflects the road alignment, traffic volumes and model receivers at the time of field measurement. A close match between model results and field measurements ensures that the models are providing accurate noise results (CDOT, 2002). The verification model covers the areas where noise level measurements were made (Figure 5 Traffic Noise Measurement Locations and Existing Sound Levels). The model was constructed in TNM using the same approach as the alternatives models (Section 2.2 Traffic Noise Modeling Methods). The two sets of results are in close agreement (Table 3 Verification Noise Model Results), as the measured and modeled results differ by less than 3 dba. The results are acceptable according to the CDOT guidelines (CDOT, 2002) which require the variation in results to be no more than 3 dba. Table 3 Verification Noise Model Results Location Number Location Measurement L eq (dba) Verification Model Result (dba) Difference (dba) block North Meadows Drive block Castlegate Drive West block US block Allen Street block North Meadows Drive block Meadows Boulevard block Castlegate Drive North block Canyon Lane Source: FHU modeling results, Traffic Noise Model Results A noise model was developed (Section 2.2 Traffic Noise Modeling Methods) to evaluate existing conditions on a broader basis than allowed by the field measurements alone. The existing conditions model included the major existing roads that may be affected by the project, with existing (2007) traffic volumes and road layouts. More than 300 points were modeled for traffic noise (Figure 6 Traffic Noise Model Receiver Locations and Appendix B). There are several existing berms (Figure 7 Existing Berms in Study Area) that were included in the models. Page 13

18 The calculated result for each model point is presented in Appendix B. Overall, the calculated noise level range for the model points was dba. Modeled points that represent two individual receivers are calculated to have existing traffic noise levels above the respective NAC during the peak hour (Figure 8 Impacted Receivers from Existing Conditions Noise Model). Both impacted receivers are Category B properties (residential); one home is in The Meadows and one is in Silver Heights. None of the Category B model points currently are at or above 75 dba (i.e., severely impacted [CDOT, 2002]). I-25 traffic is the predominant noise source for eastern portion of the study area while US 85 predominates in the center. Noise from traffic on local streets predominates in the other areas. The existing conditions model results agreed with the measurement results in that few study area locations currently meet or exceed the applicable CDOT NAC. Page 14

19 Figure 6 Traffic Noise Model Receiver Locations Source: FHU modeling data, Page 15

20 Figure 7 Existing Berms in Study Area Source: FHU project data, Page 16

21 Figure 8 Impacted Receivers from Existing Conditions Noise Model Source: FHU modeling results, Page 17

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23 4.0 ENVIRONMENTAL CONSEQUENCES The alternatives being considered for the project were described in Section 1.1 Project Description. The traffic noise modeling effort was conducted as described in Section 2.0 Analysis Methods to assess whether future noise levels near the project corridors for the alternatives would exceed relevant CDOT or FHWA thresholds. If so, mitigation measures to alleviate the predicted impacts were considered and evaluated for the build alternatives following CDOT guidelines (Section 5.0 Mitigation Evaluation). Traffic noise models were developed as described in Section 2.1 Traffic Noise Measurement for each of the alternatives. The models included the major project roads using predicted future (2030) traffic volumes and road layouts. The model noise results are tabulated in Appendix B. 4.1 No-Build Alternative 2030 Results As described in Section 2.2 Traffic Noise Modeling Methods, traffic vibration is not a concern. Therefore, only projected traffic noise impacts are relevant for No-Build Alternative and are discussed below. The results for this alternative (Figure 9 Noise Impacted Areas for No-Build Alternative-Year 2030) follow the existing conditions results. The areas impacted under existing conditions are also impacted under No-Build. The traffic noise patterns are similar to existing conditions with the noise levels pushed a bit farther from the project roads due to increased traffic volumes. This makes the impacted area larger overall and captures more impacted receivers, particularly in The Meadows. For No-Build Alternative, it has been calculated that 49 Category B receivers in the study area would be at or above the NAC and impacted by traffic noise (Table 4 Summary of Receivers Impacted by Traffic Noise). The residential areas predicted to be impacted under No-Build Alternative (Figure 9 Noise Impacted Areas for No-Build Alternative -Year 2030) are: The Meadows (19 receivers) Pines at Castle Rock/Castle Villas (24 receivers) Happy Canyon (2 receivers) Silver Heights (4 receivers) Overall, the calculated noise level range at the model points is dba. No receivers are expected to experience a 10-dBA increase; the largest increase is predicted to be 6 dba. Table 4 Property Type Summary of Receivers Impacted by Traffic Noise Existing Conditions (2007) No-Build (2030) Refined Alternative 6 (2030) Refined Alternative 7 (2030) Residential Commercial Total Source: FHU modeling results, Page 19

24 Figure 9 Noise Impacted Areas for No-Build Alternative-Year 2030 Source: FHU modeling results, Page 20

25 4.2 Refined Alternative Results As described in Section 2.2 Traffic Noise Modeling Methods, traffic vibration is not a concern. Therefore, only potential traffic noise impacts are relevant for Refined Alternative 6 and are discussed below. The results for Refined Alternative 6 are 80 Category B receivers and no Category C receivers in the study area would be impacted by traffic noise (Figure 10 Noise Impacted Areas for Refined Alternative 6-Year 2030), which is 31 more receivers than No-Build (Table 4 Summary of Receivers Impacted by Traffic Noise). Of the 80 impacted receivers, 72 are predicted to equal or exceed the NAC and eight are predicted to increase by 10 dba or more over existing conditions without reaching the relevant NAC. Overall, the calculated noise level range at the model points is dba. One of the Category B receivers is Castle View High School. Refined Alternative 6 would impact the most receivers of the alternatives. Even so, the results for Refined Alternative 6 share many similarities with both No-Build and Refined Alternative 7; many of the same receivers are predicted to be impacted. It should be noted that Refined Alternative 6 includes a longer earth berm on the north side of Castlegate Drive North for visual purposes (not traffic noise because no associated impacts were identified), but the berm provides a small noise benefit to some receivers in Castle Pines Village. The residential areas predicted to be impacted under Refined Alternative 6 are: The Meadows (35 receivers) Pines at Castle Rock/Castle Villas (40 receivers) Happy Canyon (1 receiver) Silver Heights (4 receivers) One fewer receiver in Happy Canyon would be impacted than under No-Build Alterative because Refined Alternative 6 would install an interchange that blocks some I-25 noise (Figure 2 Build Alternatives Analyzed for Noise Impacts). 4.3 Refined Alternative Results As described in Section 2.2 Traffic Noise Modeling Methods, traffic vibration is not a concern. Therefore, only potential traffic noise impacts are relevant for Refined Alternative 7 and are discussed below. The results for Refined Alternative 7 are 64 Category B receivers and no Category C receivers in the project area would be impacted by traffic noise (Figure 11 Noise Impacted Areas for Refined Alternative 7-Year 2030), which is 15 more receivers than No-Build Alternative (Table 4 Summary of Receivers Impacted by Traffic Noise) and 16 fewer than Refined Alternative 6. Of the 64 impacted receivers, 56 are predicted to equal or exceed the NAC and eight are predicted to increase by 10 dba or more over existing conditions without reaching the relevant NAC. Overall, the calculated noise level range at the model points is dba. One of the Category B receivers is Castle View High School. The results for Refined Alternative 7 share many similarities with both No-Build Alternative and Refined Alternative 6; many of the same receivers are predicted to be impacted. The residential areas predicted to be impacted under Refined Alternative 7 are: The Meadows (35 receivers) Pines at Castle Rock/Castle Villas (24 receivers) Page 21

26 Happy Canyon (1 receiver) Silver Heights (4 receivers) One fewer receiver in Happy Canyon would be impacted than under No-Build Alternative because Refined Alternative 7 would install an interchange that blocks some I-25 noise (Figure 2 Build Alternatives Analyzed for Noise Impacts). Page 22

27 Figure 10 Noise Impacted Areas for Refined Alternative 6 (Year 2030) Source: FHU modeling results, Page 23

28 Figure 11 Noise Impacted Areas for Refined Alternative 7 (Year 2030) Source: FHU modeling results, Page 24

29 4.4 Summary of Traffic Noise Impacts A number of traffic noise impacts were predicted for each of the alternatives for The predicted impacts (without mitigation) are summarized in Table 4 Summary of Receivers Impacted by Traffic Noise. There are two primary considerations that separate the alternatives: No-Build would not impact receivers along North Meadows Drive north of Butterfield Crossing Drive while Refined Alternatives 6 and 7 would Refined Alternative 6 would impact apartments along Castlegate Drive North that the other alternatives would not impact The order from fewest traffic noise impacts to most impacts for the alternatives (without mitigation) would be No-Build, Refined Alternative 7, and Refined Alternative Construction Noise Adjoining properties in the study area could be exposed to noise from construction activities from the build alternatives. Construction noise differs from traffic noise in several ways: Construction noise lasts only for the duration of the construction event, with most construction activities in noise-sensitive areas being conducted during hours that are least disturbing to adjacent and nearby residents. Construction activities generally are short term and, depending on the nature of the construction operations, could last from seconds (e.g., a truck passing a receiver) to months (e.g., constructing a bridge). Construction noise is intermittent and depends on the type of operation, location, and function of the equipment, and the equipment usage cycle. Construction noise is not assessed like operational traffic noise; there are no CDOT NACs for construction noise. Construction noise would be subject to relevant local regulations and ordinances, and any construction activities would be expected to comply with them. Portions of the project corridors abut residential areas. To address the temporary elevated noise levels that may be experienced during construction, standard mitigation measures shall be incorporated into construction contracts, where it is feasible to do so. These would include: Exhaust systems on equipment would be in good working order. Equipment would be maintained on a regular basis, and equipment may be subject to inspection by the project manager to ensure maintenance. Properly designed engine enclosures and intake silencers would be used where appropriate. New equipment would be subject to new product noise emission standards. Stationary equipment would be located as far from sensitive receivers as possible. Most construction activities in noise sensitive areas would be conducted during hours that are least disturbing to adjacent and nearby residents. Page 25

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31 5.0 MITIGATION EVALUATION The results from the traffic noise analysis indicate that many receivers would be impacted by noise from each of the alternatives. Therefore, potential mitigation actions for the impacted receivers under the build alternatives were investigated in accordance with relevant guidelines (CDOT, 2002; FHWA, 1995). Impacted areas are not guaranteed mitigation measures under these guidelines, but mitigation measures for the areas must be evaluated for feasibility and reasonableness. Reasonableness includes assessment of mitigation benefits and costs. Noise impacts from the alternatives were previously described (Section 4.0 Environmental Consequences). Several types of noise mitigation were considered. Barriers are a common mitigation action and were evaluated, but other kinds of mitigation were also considered. The overall feasibility and reasonableness of noise abatement actions that provide a substantive benefit for the impacted receivers were evaluated. Those actions found to be feasible and reasonable were then recommended for inclusion in the project. For reasons described below, barriers appear to be the only viable mitigation action and are the only mitigation evaluated through modeling. CDOT has several criteria to evaluate noise barriers (CDOT, 2002). CDOT s required minimum noise reduction is 5 dba for a barrier to be feasible, with a 10-dBA reduction goal. 5.1 Existing Noise Barriers There currently are several traffic noise barriers in the project area (Figure 7 Existing Berms in Study Area) primarily along I-25. These barriers are earth berms, although the barrier near Silver Heights also includes substantial retaining walls. The berms were included in the traffic noise modeling and the model results showed that the existing barriers are effective at reducing traffic noise to the homes behind the barriers. There is an important consideration regarding the existing barriers and whether new construction from the project would require removal of an existing barrier. The current project designs do not involve removal of any existing barriers; however, the berm along I-25 at Castle Pines Village would need to be modified for the Refined Alternative 7 interchange ramp with approximately 200 feet of berm being replaced by a wall. Refined Alternative 6 does involve addition to the berm along Castlegate Drive North (for visual purposes, not noise reduction). If through an unforeseen circumstance any of the existing barriers must be removed for project construction, the removed barrier would be replaced with an equivalent or better barrier as part of the selected alternative. The details of a replacement barrier would be determined during final design of the construction element relevant to the barrier. It is important to understand that any barrier replacements would not be new noise mitigation actions because the old barriers are products of previous projects. Barrier replacement is considered to be the restoration of infrastructure disturbed by construction. Therefore, the feasibility and reasonableness of replacement barriers was not evaluated for this project. 5.2 Evaluation of Mitigation Other than Barriers CDOT guidelines require the evaluation of several non-barrier mitigation options. For a variety of reasons that are described below, none of these options appear to be viable for the project alternatives. Traffic management measures such as lane closures or reduced speeds could reduce noise but broad application of these concepts is not reasonable for the roads of primary interest to the Page 27

32 project or compatible with the purpose of the project. One of the reasons for the proposed improvements in the regional study area is to enhance access and traffic flow. Nevertheless, traffic management concepts were applied during development of the build alternatives to minimize impacts. For example, the proposed speed limit on North Meadows Drive was set at 35 MPH rather than 45 MPH. The traffic management actions that are practical have been incorporated into the alternatives and are not available as separate noise mitigation actions. Changes in horizontal alignments of the roads near the impacted receivers could reduce noise but have limited possibilities as a separate mitigation because this concept was applied during development of the build alternatives to minimize impacts. For example, the extension of Castlegate Drive North to I-25 in Refined Alternative 6 purposely takes a path farther south in an effort to avoid impacts to Castle Pines Village. In addition, many of the impacted Category B receivers are in areas that are developed on both sides of the roads, limiting possible horizontal realignments. Relocating a street away from some impacted receivers could reduce traffic noise in those areas but could transfer the impacts to other neighboring areas or require disruptions of established adjoining property uses. There does not appear to be other reasonable horizontal relocation choices that have not already been incorporated into the build alternatives. Changes in vertical alignments (cuts or fills) could reduce noise. Changes in vertical alignments were included for some parts of some alternatives in the project area. For example, the elevated roundabout interchanges proposed on US 85 would provide shielding to some nearby receivers. However, wholesale changes in road elevations, such as along US 85, could have secondary impacts to connecting or adjoining roads that would not be reasonable or desirable. Other undesirable impacts, such as to drainage, could be created this way. In some project areas, the steep natural terrain limits options for changing vertical alignments (e.g., I-25 to US 85). In summary, vertical elevation changes were evaluated, but additional vertical realignments just to reduce traffic noise are not practical. Noise buffer zones could reduce noise levels, but there are limited opportunities in the study area due to prior zoning and platting of local land use. Often, prior development has been purposely built near the roads for access, which leaves little or no space for a buffer. In the few places where there may be space, there generally are no nearby impacted receivers. Supplemental building insulation is an extraordinary abatement method that may be used when other mitigation measures are not practical. However, no residences were calculated to be severely impacted by traffic noise (at least 75 dba), so consideration of noise insulation measures is not justified. Pavement types and surfaces can affect traffic noise. Research efforts to learn more about the long-term noise benefits of different pavement types and surface treatments are ongoing. Quieter pavement types can be preferred for the project when minimum requirements for safety, durability and other materials requirements are also met. However, this cannot be counted as a mitigation action under the noise reduction evaluation because it is not a permanent solution. 5.3 Assessment of Nonproject Impacts Numerous traffic noise impacts are identified for the study area through the noise analysis (Section 4.3 Refined Alternative Results). However, several of these noise impacts are not due to or changed by the proposed build alternatives; rather the impacts are due to growth on the major study area roads (I-25 and US 85). For example, the noise model results for the build alternatives are the same as or lower than the results for No-Build for the impacted receivers in Happy Canyon, Silver Heights, Castle Villas and several of the Pines at Castle Page 28

33 Rock (Appendix B). The model results are the same where the build alternatives are indistinguishable from No-Build and the changed traffic noise is not important in the overall results. The model results are lower when the build alternatives would add a ramp that would actually provide a noise benefit to receivers by blocking some traffic noise. Therefore, the build alternatives are not the source of these noise impacts; rather the improvements in the build alternatives happen to pass near these impacts, which are then captured in the noise analysis. I-25 and US 85 were also important considerations in the previous EIS (CDOT, 2001) and some noise mitigation was recommended. Reasons for differences between the older EIS results and the current EA results have been described in Section 3.1 Previous Studies. The primary traffic growth on I-25 and US 85 will not be due to the North Meadows Extension project. Because the build alternatives are not the source of the traffic noise impacts for Happy Canyon, Silver Heights, Castle Villas and several of the Pines at Castle Rock, noise barriers for these areas have not been evaluated for this noise analysis and are not discussed in Section 5.4 Traffic Noise Barrier Evaluations. 5.4 Traffic Noise Barrier Evaluations In addition to the existing berms, noise barriers in some new areas may be appropriate for an alternative. To permit the evaluation of new noise barriers, computer models of barriers protecting the impacted areas were developed. Each potential barrier was assessed for effectiveness and feasibility. If the minimum parameters for an effective barrier were met and the barrier was feasible, the barrier was processed through a reasonability assessment according to CDOT guidance (CDOT, 2002). The feasibility and reasonableness of each barrier determined whether the barrier was recommended for the project (Appendix D). The locations evaluated for new noise barriers are shown in Figure 12 Locations of Traffic Noise Mitigation Barriers Evaluated. In instances where only part of a neighborhood was impacted by traffic noise, barriers benefiting the entire neighborhood were evaluated for thoroughness. Each of these various barriers were assessed for feasibility and reasonableness (CDOT, 2002), and barrier recommendations were made based on these findings. The typical locations for the mitigation barriers were at the edge of road right-of-way (Appendix C). It is important to note that the noise barriers can be earth berms or constructed walls and that many materials can be effective barriers. Berms can be very effective but occupy considerably more space than comparable walls. Throughout the project area, the impacted receivers tend to be rather close to the project roads. This usually makes earth berms impractical or impossible choices for the noise barriers. Barrier cost-effectiveness was based on an assumed cost of $30/square foot of barrier and compared to the CDOT upper threshold of $4,000/receiver/decibel. The barrier evaluation results (Appendix D) are summarized in Table 5 Traffic Noise Mitigation Barrier Summary. Page 29

34 Figure 12 Locations of Traffic Noise Mitigation Barriers Evaluated Source: FHU modeling results, Page 30

35 Table 5 Traffic Noise Mitigation Barrier Summary Noise Impacted Category B Area Barrier Height (feet) Barrier Length (feet) Cost Analysis ($/receiver/dba) Noise Reduction (dba) Feasible? Reasonable? Recommended? Comment The Meadows # , Yes Yes Yes The Meadows # , Yes Yes Yes The Meadows # , Yes Yes Yes Pines at Castle Rock # ,050 6 Yes Yes Yes Source: FHU modeling results, Recommended for Refined Alternatives 6 and 7 Recommended for Refined Alternatives 6 and 7 Recommended for Refined Alternatives 6 and 7 Recommended for Refined Alternative 6 The Meadows Homes in The Meadows for approximately a half-mile along North Meadows Drive are predicted to be impacted by traffic noise under Refined Alternatives 6 and 7 (Appendix C). These homes are even with to slightly above North Meadows Drive in elevation. A barrier in three segments extending along North Meadows Drive (Figure 12 Locations of Traffic Noise Mitigation Barriers Evaluated) is needed to allow for intersecting streets and each barrier segment is evaluated separately. Segment 1 (Meadows Boulevard to West Indian Summer Lane), 360 feet long by 6 feet high, is calculated to provide 3-6 dba of noise reduction for three homes. Segment 2 (West Indian Summer Lane to Butterfield Crossing Drive), 1100 feet long by 6-8 feet high, is calculated to provide 3-6 dba of noise reduction for about 27 homes. Segment 3 (Butterfield Crossing Drive to railroad underpass), 800 feet long by 6-8 feet high, is calculated to provide 4-6 dba of noise reduction for about 13 homes. Though these are three physically distinct barriers, they have been viewed as a neighborhood group and the three segments fit the CDOT benefit-cost guideline (Appendix D); all are being recommended for Refined Alternatives 6 and 7 (Table 5 Traffic Noise Mitigation Barrier Summary). Pines at Castle Rock Two multi-unit residential buildings along Castlegate Drive North are predicted to be impacted by traffic noise under Refined Alternative 6 (Appendix C). These homes are approximately even with Castlegate Drive North in elevation. A barrier along Castlegate Drive North (#4, Table 5 Traffic Noise Mitigation Barrier Summary) 550 feet long by 6 feet high, is calculated to provide 4-7 dba of noise reduction for the two buildings. This barrier fits the CDOT cost guideline (Table 5 Traffic Noise Mitigation Barrier Summary) and is being recommended for Refined Alternative 6 (Appendix D). Page 31

36 Castle View High School A corner of the Castle View High School building is calculated to exceed the Category B NAC for Refined Alternatives 6 and 7. The building is higher in elevation than North Meadows Drive. This part of the school is a remote corner that does not have any visible exterior uses and consists of building structure and landscaping next to North Meadows Drive. A barrier here would provide no real benefit to the school. Other actively-used parts of Castle View High School are calculated not to be impacted by noise. For these reasons, a barrier was not considered for this location. 5.5 Summary of Recommended Mitigation The recommendations provided above and summarized here were based on specific project design conditions. If the final designs in the future differ from the designs examined here, corresponding adjustments to the mitigation evaluations may be required. The overall traffic noise barrier findings are summarized in Table 5 Traffic Noise Mitigation Barrier Summary. The traffic noise reductions for each barrier are estimated. The project recommendations are for select barriers to be included within the road right of way. From the feasibility and reasonableness evaluations for the barriers, traffic noise barriers are recommended (and will be built along with the selected road improvements) between traffic and receivers for locations 1, 2, 3 and 4 illustrated in Figure 12 Locations of Traffic Noise Mitigation Barriers Evaluated, addressing the following neighborhoods: The Meadows (Refined Alternatives 6 and 7) Pines at Castle Rock (Refined Alternative 6) 5.6 Impacted Receivers After Recommended Mitigation For a noise mitigation action to be recommended, it must be both feasible and reasonable according to the evaluation guidelines. In some of the areas identified with traffic noise impacts (Section 4.0 Environmental Consequences), noise barriers were determined to be not appropriate (Section 5.3 Assessment of Nonproject Impacts). Therefore, not all areas identified with impacts have been recommended for noise mitigation. The recommended mitigation actions would serve to reduce noise impacts for each of the build alternatives (Section 5.4 Traffic Noise Barrier Evaluations). The final results can differ between the build alternatives for a number of reasons, including: Different road alignments Different traffic volumes and speeds Different vertical road profiles The recommended mitigation actions would not eliminate all of the calculated noise impacts; some noise impacts would remain. These remnant noise impacts are described below for each of the alternatives. No-Build Alternative The No-Build Alternative does not include any new noise mitigation actions, so there would be no change in the traffic noise impacts (Section 4.1 No-Build Alternative 2030 Results). The same 49 Category B receivers would still be impacted by traffic noise (Figure 9 Noise Impacted Areas for No-Build Alternative -Year 2030). Page 32

37 Refined Alternative 6 Refined Alternative 6 would include the most mitigation actions (Section 5.4 Traffic Noise Barrier Evaluations). The recommended mitigation measures would remove the traffic noise impacts from these receivers: The Meadows 33 Category B receivers Pines at Castle Rock 16 Category B receivers An estimated 31 Category B receivers would still be impacted by traffic noise, which are 18 receivers fewer than for the No-Build Alternative (Figure 13 Traffic Noise Impacts After Recommended Mitigation Actions). Refined Alternative 7 Refined Alternative 7 would include several mitigation actions (Section 5.4 Traffic Noise Barrier Evaluations). The recommended mitigation measures would remove the traffic noise impacts from 33 Category B receivers in the Meadows. An estimated 31 Category B receivers would still be impacted by traffic noise, which are 18 receivers fewer than for the No-Build Alternative. Page 33

38 Figure 13 Traffic Noise Impacts After Recommended Mitigation Actions Source: FHU modeling results, Page 34

39 Technical Report 6.0 REFERENCES Colorado Department of Transportation South I-25 Corridor and US 85 Corridor Final Environmental Impact Statement, May. Colorado Department of Transportation Noise Analysis and Abatement Guidelines, December. Colorado Department of Transportation North Meadows Extension to US 85 & I-25, May. Federal Highway Administration Highway Traffic Noise Analysis and Abatement Policy and Guidance, June. Federal Highway Administration Measurement of Highway-Related Noise, May. Federal Highway Administration Procedures for Abatement of Highway Traffic Noise and Construction Noise. Code of Federal Regulations, Title 23, Part 772. Felsburg Holt & Ullevig Traffic data for the Meadows Extension Project, January. Page 35

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41 APPENDIX A NOISE MEASUREMENT DATA Appendix A

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51 APPENDIX B NOISE MODEL RECEIVERS AND RESULTS Appendix B

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53 Legend Noise Model Receiver Proposed Study Area Railroads Highways Major Arterial Local Roads Feet