4.3 Noise and Vibration - Seattle Streetcar CITY CONNECTOR STREETCAR NOISE AND VIBRATION . ......

CENTER CITY CONNECTOR STREETCAR NOISE AND VIBRATION

4.3 Noise and Vibration Noise and vibration are common in an urbanized area. Increases in noise can cause sleep disturbances and general annoyance or uneasiness. Increases in vibration can sometimes be felt and have the potential to affect buildings. Potential impacts of noise and vibration from transportation projects must be measured and evaluated in order to protect areas where people sleep, where there are functions that depend on quiet, or where there is a potential to affect adjacent structures. This section describes potential noise and vibration impacts of the Center City Connector. The project study area, consists of sensitive receptors within 125 feet of the alignment centerline for noise and up to 200 feet for vibration, depending on building material.

4.3.1 Noise Noise is defined as unwanted sound, which is a subjective experience of exposure to different sound levels. The human ear processes small fluctuations in air pressure differently, depending on the amplitude (loudness and softness), pitch (high or low frequency), and variability (how noise changes over time). Sound pressure is measured in terms of sound pressure level, expressed in decibels (dB). The overall dB level does not address the varying human sensitivity to sound at different frequencies or overall loudness that might be experienced.

4.3.1.1 Measuring Noise The human ear is optimized for speech frequencies and is less sensitive at low frequencies and very high frequencies. To provide a measurement meaningful to humans, a weighting system was developed that reduces contributions of these higher- and lower-frequency sounds. This filtering system is used for nearly all noise ordinances. Measurements taken with this “A-weighted” filter are referred to as “dBA” readings.

4.3.1.2 Evaluating Noise Impacts Sound pressure levels vary in magnitude over time, often significantly. Human sensitivity to noise also varies over time, with nighttime sensitivity typically being higher than daytime. In order to account for this, descriptors have been developed for use in determining noise impacts by simplifying the description of a complex time and varying sound pressure level into single-digit numbers. The three most common descriptors used for assessing environmental impacts are the equivalent sound level (Leq), the day-night sound level (Ldn), and the maximum sound level (Lmax), defined as follows:

Human Response to Sound

The human ear has a unique response to sound pressure. It is less sensitive to sounds falling outside the speech frequency range. Sound-level meters and monitors use a filtering system to approximate human perception of sound. Measurements made using this filtering system are referred to as A-weighted.

Applicable Regulations

Noise and Vibration impacts are based on FTA guidance manual Transit Noise and Vibration Impact Assessment (FTA, 2006) and Seattle Noise Control Code (Seattle Municipal Code [SMC] Chapter 25.08) which specifies permissible sound levels within the city.

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Leq – steady sound level that represents the same sound energy as the varying sound levels over a specified time period (typically 1 hour or 24 hours).

Ldn – 24-hour Leq with a 10-dB penalty to sound levels at night, accounting for increased sensitivity when people typically sleep. This is typically applied to residential receptors.

Lmax – the loudest event with a given time period, most commonly 1 hour.

Noise impacts for the project are based on the criteria defined in the FTA guidance manual Transit Noise and Vibration Impact Assessment (FTA, 2006).

FTA’s noise impact criteria are grouped into the following noise-sensitive receptor categories, based on land use:1,2

Category 1: Buildings or parks where quiet is an essential element of their purpose.

Category 2: Residences and buildings where people normally sleep, including residences, hospitals, and hotels where nighttime sensitivity is assumed to be important.

Category 3: Institutional land uses with primarily daytime and evening use, including schools, libraries, churches, and active parks.

There are two levels of impact included in the FTA criteria:

Severe impact: Project-generated noise in the severe impact range would cause a substantial percentage of people to be highly annoyed by the new noise and represents the most compelling need for mitigation.

Moderate impact: In this range of noise impact, the change in the cumulative noise level is noticeable to most people but might not be sufficient to cause strong, adverse reactions from the community. Other project-specific factors must be considered to determine the magnitude of the impact and the need for mitigation.

Figure 4.3-1 depicts the noise impact criteria, as well as the existing noise exposure and the additional noise exposure from a transit project that would cause either moderate or severe impacts. The future noise exposure is determined by combining the existing noise exposure and the additional noise exposure that a transit project would cause.

4.3.1.3 Seattle Noise Ordinance The Seattle Noise Control Code (Seattle Municipal Code [SMC] Chapter 25.08) specifies permissible sound levels within the city. SMC 25.08.410 defines limits for exterior sound levels between properties based on zoning districts. Table 4.3-1 lists permissible sound levels transmitted between unrelated properties.

1 Ldn is used to characterize noise exposure for residential areas (Category 2). For other noise-sensitive land uses, such as outdoor amphitheaters and school buildings (Categories 1 and 3), the highest 1-hour Leq during the facility’s operating period is used. 2 Parks are considered a special case under the FTA criteria. Only parks that are primarily used for passive activities, such as reading, conversation, and meditation, in contrast, could be considered noise-sensitive, and the parks must have low existing noise levels. In addition, outdoor areas where interpretation takes place, such as historic landmarks or tours, could be considered under the FTA criteria.

Sensitive Receptors

Sensitive receptors are locations where occupants’ use may be altered by excessive noise. Sensitive receptors commonly include residences, health care facilities, public libraries, schools, and parks.



Modifications to the exterior sound level limits are subject to modifications delineated in SMC 25.08.420, depending on the time of day, classification of receiving properties, and the type of sound generated. These modifications are additive and independent of one another. Therefore, the exterior nighttime sound level limit in a residential district for a periodic, tonal source would be 20 dB less than the exterior sound level limits listed in Table 3.4-1.

While the SMC does not regulate noise emissions from streetcars operating on their public alignments, these regulations do apply to both OMF expansion sites, as shown in Table 4.3-2.

Table 4.3-1 City of Seattle Exterior Sound-Level Limits

District of Sound Source

District of Receiving Property (Hourly Leq / Lmax)

Residential Commercial Industrial

Residential 55 / 70 57 / 72 60 / 75

Commercial 57 / 72 60 / 75 65 / 80

Industrial 60 / 75 65 / 80 70 / 85

Source: SMC 25.08.410, Exterior Sound Level Limits.

Table 4.3-2 OMF Sound-Level Limits

Facility District of Sound

Source District of Receiving

Property Code Limit

(Hourly Leq / Lmax)

South Lake Union Commercial Commercial 60 / 75

Chinatown-International District Commercial

Commercial 60 / 75

Industrial 65 / 80

Source: SMC Chapter 25.08.

Figure 4.3-1 FTA Project Noise Impact Criteria

Source: FTA (2006)



4.3.1.4 Noise in the Study Area The project noise study area is defined as all noise-sensitive receptors within 125 feet of the centerline of the streetcar alignment and properties near the OMF expansion sites. Within the overall study area, including the LPA (discussed in detail in the Appendix H3, Center City Connector Noise and Vibration Technical Report [SDOT, 2015]), there are a total of 67 noise-sensitive receptors that were investigated, 94 percent of which were residential use. Existing sound levels within this study area range between 66 and 76 dBA during the day and 64 and 67 dBA at night.

4.3.2 Vibration 4.3.2.1 Vibration Overview Streetcar operations on tracks and crossovers can result in vibration that might be felt on adjacent properties. For vibration, there are a total of 128 sensitive receptors within the vibration study area (i.e., 200 feet from streetcar alignment centerline), 49 percent of which are residential use. Vibration above certain levels can damage buildings, disrupt sensitive operations, and annoy humans in buildings. The response of humans, buildings, and equipment to vibration is most commonly described using velocity. Vibration velocity level or VdB is used to evaluate the effects of vibration on humans and equipment. Damage to buildings is assessed using the peak particle value (PPV).

Figure 4.3-2 illustrates typical groundborne vibration velocity levels for common sources, as well as thresholds for human and structural response to groundborne vibration. The threshold of human perception to vibration is approximately 65 VdB; annoyance does not usually occur unless the vibration exceeds 70 VdB.

4.3.2.2 Vibration Criteria FTA’s groundborne vibration impact criteria are based on existing land use and the number of train pass-bys per hour. The FTA vibration criteria are applied primarily to residential (including hotels and other places where people sleep) and institutional land uses. Table 4.3-3 shows the criteria for a general vibration assessment. Commercial land uses are only considered when they contain vibration-sensitive uses, such as medical offices or sensitive manufacturing equipment. Other buildings, such as concert halls, recording studios, and theaters, can be very sensitive to vibration and have criteria ranging between 65 and 72 VdB for frequent events, defined as more than 70 vibration events per day.

FTA categorizes most receptors in the study area as vibration-sensitive receptors. These receptor categories are different than the noise-sensitive receptor categories, with the exception of Category 2 being residential use. A single Category 1 receptor was identified (Parcel ID #178, Institute for System Biology, 401 Terry Avenue N) because it includes biomedical research activities. Although this area was previously studied for the South Lake Union Streetcar (Parsons Brinckerhoff, 2005), it is not clear if this property was used as a medical research facility at that time.



Table 4.3-3 Groundborne Vibration and Noise Impact Criteria for Light Rail Transit Service Frequency

Land Use Category

Groundborne Vibration Impact Levels

(VdB re 1 micro inch/second): Frequent Events

Groundborne Noise Impact Levels

(dB re 20 micro Pascals): Frequent Events

Category 1: Buildings where low ambient vibration is essential for interior operations

65 VdBa N/Ab

Category 2: Residences and buildings where people normally sleep

72 VdB 35 dBA

Category 3: Institutional land uses with primarily daytime use 75 VdB 40 dBA

a This criterion limit is based on levels that are acceptable for most moderately sensitive equipment, such as optical microscopes. Vibration-sensitive manufacturing or research would require detailed evaluation to define the acceptable vibration levels. Verifying lower vibration levels in a building often requires special design of the heating, ventilation, and air conditioning systems and stiffened floors. b Vibration-sensitive equipment is generally not sensitive to groundborne noise.

Figure 4.3-2 Examples of Groundborne Vibration Levels and Human/Structural Response

Source: FTA (2006)



4.3.3 Impacts 4.3.3.1 No Build Alternative The No Build Alternative would not result in project-related noise or vibration impacts. The urban environment would continue to have noise from development construction and from traffic, which are projected to increase based upon forecasted increases in population and employment in Seattle (see Section 4. 6, Social and Community Effects).

4.3.3.2 Locally Preferred Alternative

Operational Impacts

Noise Detailed noise and vibration prediction models were developed using the methods given in the FTA’s Transit Noise and Vibration Guidance Manual (revised May 2006) (FTA, 2006b). The prediction models involve gathering ambient noise by taking measurements over a 24-hour period to determine existing noise conditions. Then prescribed FTA inputs for streetcar noise such as the sound level at 50 feet from the streetcar, number of trains per hour, travel speed, and existing background noise are combined in the model to “predict” project sound levels. If the predicted sound level at the exterior of a sensitive receptor exceeds the criteria set by FTA, a preliminary impact is noted. Table 4.3-4 provides the noise input descriptions used to predict noise from the project.

Table 4.3-4 Streetcar General Noise Assessment Input Parameters

Description Value

Reference SEL at 50 feet for street cara 82 dBA

Average number of cars per streetcar set 2

Travel speed 25 mph

Average hourly volume of traffic 18 trains per hour

Average daytime hourly volume of traffic 23 trains per hour

Peak daytime hourly volume of traffic 24 trains per hour

Average nighttime hourly volume of traffic 10 trains per hour

Rail vehicles adjustment (embedded on grade)b 3

Source: FTA Manual, Table 5-1. a SEL = sound exposure level b Track can be embedded in asphalt, concrete, ballast material, or in groomed ground. The LPA is planned to be in concrete.

Conservative input data of 25 mph was used for the entire Center City Connector alignment, generating a worst-case noise scenario. During operations, the streetcar would not reach this speed throughout the alignment because streetcars must slow at station stops and signalized intersections; in addition, on other portions of the route, streetcars would travel in mixed flow



with motorized vehicles and adjust to lower speeds. For the Center City Connector, 25 mph is conservative because the average speed would be closer to 15 mph over the length of the project.

Measurements were conducted to document existing noise conditions at representative locations along the alignment. Monitoring stations, shown on Figure 4.3-3, were located near proposed station locations in proximity to residential use (Category 2) receptors, where feasible. Table 4.3-5 lists the specific locations and durations for noise monitoring.

Table 4.3-5 Ambient Noise Monitoring Locations

Location Address Duration

N-1 1903 5th Ave, surface parking lot near Westin Hotel, Parcel ID #162

10/1/14 – 10/2/14

N-2 1902 2nd Ave, The Josephinum, Parcel ID #154 10/28/14 – 10/29/14

N-3 1423 First Avenue, Providence Vincent House, Parcel ID #136

10/20/14 – 10/21/14

N-4 1000 1st Ave, Hotel 1000/Madison Tower Condos, Parcel ID #114

10/10/14 – 10/11/14

N-5 315 Maynard Ave S., International Apartments, Parcel ID #46 10/27/14 – 10/28/14

N-7 (OMF) 312 Fairview N, South Lake Union Streetcar OMF 11/20/14 – 11-21/2014

Sound travels outward from the point where it is generated. As the distance increases, sound levels are reduced. Noise impacts were determined by calculating the distance from the track centerline to the location where the predicted sound levels would have an impact (based on impact levels shown on Figure 4.3-1). It is assumed that there would be an impact on any property within this noise buffer. These noise buffer distances vary for each noise source (rolling noise on track, crossovers, and bells) and adjacent land use.

According to the noise model, operation along the alignment (without stations and stops) at 25 mph would result in two moderate impacts. These would occur along the alignment at the Jackson Square Condos and the Fisher Building. This is shown in Table 4.3-6 in the “Streetcar” column.

Impact buffers were calculated separately for stations, tracks between stations, crossovers, and for bells sounded on approach and departure from each station. According to the model, the crossovers could result in eight moderate and four severe impacts at the crossovers (see Table 4.3-6 – “Crossover” column). In addition, two moderate impacts were predicted from the bells at the stations.

Noise at Crossover/Turnback Tracks

When a streetcar passes over the crossover (see photograph) it can make a clanking sound at a different frequency than a streetcar traveling on an unbroken track. Therefore, crossover sounds are modeled separately. Crossover tracks may be used for turnbacks.



Figure 4.3-3 Noise Monitoring Locations and Impacts at 25 MPH



Table 4.3-6 Streetcar Noise Impact Summary

Parcel ID

Description (all Category 2 Receptors) Streetcar

Wheels on Rail Bells Crossover

Total Impact Modeled at

25 mpha

Resulting Impact at Operating Speed of

15 mph or less Impact Locations

9 Don Hee Apts. - - Moderate Moderate None

44 Bush Hotel - - Moderate Moderate None

46 Far East Building - - Moderate Moderate None

49 Buty Building - - Moderate Moderate None

50 Governor Apts. - - Severe Severe None

63 Cadillac Hotel - - Moderate Moderate None

66 Jackson Square Condos

Moderate Moderate Severe Severe Noneb

67 Fisher Building Moderate Moderate Moderate Severe Noneb

135 Hahn Building - - Moderate Moderate None

136 98 Union Condos - - Severe Severe None

168 Westin Hotel - - Severe Severe None

170 Metropolitan Tower

- - Moderate Moderate None

a Lower speeds were modeled that indicated noise impacts are eliminated at these lower speeds. b Seattle streetcar bells at stations are measured to be lower than FTA model inputs and therefore moderate impacts from bells are avoided.

Streetcar Noise Impacts. All operational impacts predicted for the Center City Connector at lower average travel speeds of 15 mph would be eliminated (Parcel ID #s 66 and 67) near the station stops.

Moderate and severe noise impacts predicted at the crossovers would be eliminated because (1) the speed of the trains near stations and mixed-flow traffic conditions would be much lower than the 25 mph used in the model and (2) the fact that actual noise measurements of crossovers at the existing South Lake Union alignment are lower than the FTA Manual inputs used in the model. Streetcar bells at stations would have moderate impacts on two properties (parcel ID#66 and 67). However, the Seattle Streetcar bells are quieter than the FTA standard level for bells (based on measurements made of streetcars on the existing South Lake Union line) during normal operations and are further decreased during evening hours, reducing the 24-hour Ldn used to predict impacts reported in Table 4.3-6, which is the measurement used to assess impacts at Category 2 (residential) receptors.

Operations and Maintenance Facilities Noise Impacts. Noise-generating activities (such as use of power tools and compressors) occur inside maintenance buildings at the existing South Lake Union OMF with the roll-up doors closed; the only activities that occur outside are hand-washing and cleaning of the streetcars. As streetcars enter and exit the South Lake Union OMF, typically at 5 mph or less, warning bells sound. Noise monitoring of the existing facility



(locations shown on Figure 4.3-3) revealed sound levels of Ldn 73, which includes sound emissions from the OMF and other ambient noise sources such as traffic and local construction.

This existing condition would result in an impact threshold of Ldn 65, even though the existing ambient level is Ldn 73, the upper criteria limit for FTA is Ldn 65. Streetcar traffic along the OMF access tracks were modeled for each operating scenario (6 more street cars or consolidation all 16 streetcars). These operations, in addition to crossover and bell noise emissions, are anticipated to result in no noise impacts along these access tracks at either OMF location.

Vibration To determine existing groundborne vibration levels along the LPA alignment, measurements were made at two representative locations to characterize the transfer mobility (a measure of how efficiently vibration travels through the ground). A third location is referenced from data from another public project in the vicinity (see Figure 4.3-4). Vibration propagation testing was conducted on October 21, 2014, at 801 Second Avenue, the Norton Building, (Parcel ID #109 [Category 3]), and 117 First Avenue S (Parcel ID #94 [Category 2]). Testing locations are shown on Figure 4.3-4. Measured propagation losses (how quickly vibration attenuates in the soil with an increase in distance from the source) were consistent with FTA guidelines for general vibration analysis. Test results also demonstrated that an areaway (which are like a walkable basement located under the sidewalks) presented a reduced level of vibration in the soil above and on the opposite side of the area for the same input force near the alignment. It is likely that the areaway reduces the amount of groundborne vibration, because of the discontinuity between the soil and areaway. Areaways are only a concern for vibratory damage. An arreaway3 would not experience vibration at levels that could result in damage.

Vibration emissions from streetcar operations under typical track conditions (without crossovers) were calculated in accordance with FTA Manual, Chapter 10, General Vibration Assessment (FTA, 2006). Using computation methodologies in the FTA Manual, and the LPA operation input of 25 miles per hour, vibration levels were calculated at 50 feet (as required by the FTA Manual) for a typical 2-story masonry building for typical operations and for areas where crossovers may affect vibration levels. Results are listed in Table 4.3-7.

Table 4.3-7 Predicted Streetcar Groundborne Vibration and Noise Levels at 50 feet for a Two-Story Masonry Building

Receptor Description VdB dBA

Streetcar Operations 64 14

Crossover 74 24

Vibration impacts were determined by calculating the distance between the track centerline to equal the impact threshold (as shown in Table 4.3-3). Any receptor within these buffer distances (which vary by vibration source—trackwork versus crossover—and by receptor category) that equals the threshold would be associated with a predicted groundborne noise or vibration level that exceeds the criteria and is thereby identified as a potential impact. Receptors beyond that

3 Areaway are typically under the sidewalk attached to the building as an extended basement. The Center City Connector is proposed in the center lanes of the roadway; therefore, the streetcar would be at least one travel lane, or approximately 11 to 12 feet, away from the areaways. The exception is along Stewart Street, but no vibratory impacts are anticipated at levels that would induce damage.



Figure 4.3-4 Vibration Monitoring and Vibration Impacts



impact buffer distance would experience vibration levels below the FTA impact criteria and would not result in a vibration impact.

A receptor is considered affected if the impact buffer extends into the property boundary, which is conservative in the case of a building that is set back from the parcel boundary. Table 4.3-8 lists the locations and sources of potential vibration impacts (where the impact buffer extends into the property boundary), and Figure 4.3-4 above shows the locations with respect to the LPA.

Table 4.3-8 Streetcar Operational Vibration Impacts for the LPA

Parcel ID

Address Description Category Streetcar or Crossover

45 601 S Jackson St Washington Federal 3 Crossover

50 526 S Jackson St Governor Apartments 2 Crossover

62 157 S Jackson St Washington Shoe Co. 3 Crossover

64 308 Occidental Ave S Occidental Mall 3 Crossover

66 123 S Jackson St Jackson Square Condos 2 Crossover

168 1900 5th Ave Westin Hotel 2 Crossover

178 401 Terry Ave N Institute for Systems Biology 1 Streetcar and Crossover

The following sections present a brief analysis of the receptors where vibration impacts were predicted. The analysis to determine the impacts described in Table 4.3-8 above assumed a two-story masonry building located on the lot line, which presented a conservative analysis case. For all the identified impacts, refinements to the analysis were made on a property-by-property basis to investigate vibration impacts based on actual building size, distance from the alignment, and lowest floor of vibration-sensitive use.

601 S Jackson Street, Washington Federal (Parcel ID #45). This property includes a two-story office building 38 feet from the alignment, with minimal setback. The 2-dB floor-to-floor attenuation would reduce the second floor to below the impact criteria of 75 VdB. Accounting for a slower travel speed along this portion of the alignment (15 mph, but likely slower), there would be no affected receptors.

526 S Jackson Street, Governor Apartments (Parcel ID #50). This property includes a two-story building 57 feet from the alignment, with minimal setback. The first floor is retail use, which is not vibration-sensitive. The 2-dB floor-to-floor attenuation would reduce the second floor to below the impact criteria of 72 VdB. As a result, there would be no affected receptors.

157 S Jackson Street, Washington Shoe Co. (Parcel ID #62). This property includes a six-story building 27 feet from the alignment, with minimal setback. The first floor is retail use, which is not vibration-sensitive; all remaining floors are commercial. The extra 3-dB coupling loss and 2-dB floor-to-floor attenuation would reduce the second floor to below the impact criteria of 75 VdB. As a result, there would be no affected receptors.

308 Occidental Avenue S, Occidental Mall (Parcel ID #64). This property includes a six-story building 27 feet from the alignment, with minimal setback. The first floor is retail use, which is not vibration-sensitive; all remaining floors are commercial. The extra 3-dB coupling loss and 2-



dB floor-to-floor attenuation would reduce the second floor to below the impact criteria of 75 VdB. As a result, there would be no affected receptors.

123 S Jackson Street, Jackson Square Condos (Parcel ID #66). This property includes a two-story building 31 feet from the alignment, with minimal setback. The first floor is retail use, which is not vibration-sensitive, and the second floor is residential use. The 2-dB floor-to-floor attenuation would not reduce the second floor to below the impact criteria of 72 VdB. Accounting for a slower travel speed along this portion of the alignment (15 mph, but likely slower), there would be no affected receptors.

1900 Fifth Avenue, Westin Hotel (Parcel ID #168). This property includes a 37-story building 43 feet from the alignment, with minimal setback. The first floor is retail use, which is not vibration-sensitive; all other floors are residential use. The extra 6-dB coupling loss due to the size of the building and 2-dB floor-to-floor attenuation would reduce the second floor to below the impact criteria of 72 VdB. As a result, there would be no affected receptors.

401 Terry Avenue, Institute for Systems Biology (Parcel ID #178). This property includes a four-story building 30 feet from the alignment. The entire building appears to be used for biomedical research, which can be vibration-sensitive. The extra 3-dB coupling loss and 2-dB floor-to-floor attenuation is not expected to reduce any floors to below the impact criteria of 65 VdB. However, it is important to note that this crossover is an existing element of the South Lake Union Streetcar line. Although this crossover may be used by Center City Connector streetcars entering and departing revenue service via the South Lake Union OMF, the Center City Connector is not expected to increase existing vibration impacts because the proposed project streetcars are expected to produce the same vibratory effects as existing streetcars and because longer or more frequent vibration events do not change the impact level. Therefore, there would be no affected receptors due to the addition of a second crossover and higher streetcar traffic on the existing crossover. For impacts due to streetcar operations, the South Lake Union Streetcar alignment currently exists east of the building. The Center City Connector project would only be adding additional track north of the building, which is not expected to increase existing vibration levels in the building.

1523 First Avenue, Market House Condos (Parcel ID# 140). This property includes a three-story building 52 feet from the alignment, with minimal setback. The first floor is retail use, which is not vibration-sensitive; all other floors are residential use. The extra 3-dB coupling loss due to the size of the building and 2-dB floor-to-floor attenuation would reduce the second floor to below the impact criteria of 72 VdB. As a result, there would be no affected receptors.

Construction Impacts

Noise The FTA Manual does not provide “standardized criteria” for determining noise impacts from construction and typically defers to codified noise levels set by local jurisdictions (see Section 3.4.2, Operations and Maintenance Facilities). However, the FTA Manual does provide “reasonable criteria for assessment” to indicate a possible “adverse community reaction.” These criteria are shown in Table 4.3-9.



Table 4.3-9 FTA Construction Noise Impact Criteria

Land Use Hourly Leq (dBA)

Daytime Nighttime Residential 90 80 Commercial 100 100 Industrial 100 100 Source: FTA Manual, Chapter 12.

Additional allowances are provided in the SMC (Seattle Noise Control Code SMC Chapter 25.08) for construction activities, raising the permissible levels for construction equipment, and allowing daytime limits between 7 a.m. and 10 p.m. on weekdays and 9 a.m. and 10 p.m. on weekends and legal holidays. Outside these construction hours, lower sound level limits discussed in Section 4.3.1.3 would apply. These lower limits also apply inside commercial buildings when all windows and doors are closed during these construction hours. Sound emissions that exceed the SMC would require a noise variance from the City of Seattle.

FTA methodologies for a general assessment (FTA Manual, Chapter 12, Noise and Vibration during Construction) include identifying the two loudest pieces of equipment for each construction stage, operating them simultaneously for 1 hour, and comparing the modeled sound levels to the FTA criteria. This conservative approach will likely overestimate sound emissions from construction, which would vary from hour to hour. However, with limited information related to equipment, means and methods, and construction sequencing at this early stage of design, the FTA Manual encourages this conservative approach.

Construction includes demolition of asphalts and potentially of a building on the proposed South Lake Union OMF expansion area. However, the two loudest enduring construction activities for the Center City Connector are anticipated to be removal of existing pavement and installation of trackwork. Removal of existing pavement would require jackhammering and hauling of materials. Trackwork would require using a rail saw and bringing in and removing concrete by truck. Sound emission predictions at 50 feet from associated activities are shown in Tables 4.3-10 and 4.3-11.

Table 4.3-10 Construction Noise General Assessment for Removal of Existing Pavement

Equipment Emission Level at

50 feet (dBA)

Usage Factor SPL at 50 feet (dBA)

Jackhammer 88 1 88

Haul Truck 88 1 88

Total 91



Table 4.3-11 Construction Noise General Assessment for Installation of Trackwork

Equipment Emission Level at

50 feet (dBA)

Usage Factor SPL at 50 feet (dBA)

Rail Saw 90 1 90

Concrete Truck 85 1 85

Total 91

Sound levels of 91 dBA (hourly Leq) were predicted for both pavement removal and trackwork. This is below the FTA noise criteria for commercial use properties (100 dBA) but would exceed both the daytime (90 dBA) and nighttime (80 dBA) criteria for residential use properties. The predicted sound level exceeds the 85 dBA sound-level limit established by the City of Seattle. When construction activities occur 50 or more feet from buildings, sound-level limits inside buildings located on commercial zoned properties are typically satisfied. However, when work occurs closer, noise control measures may be required to satisfy interior sound-level limits. Contractors would be required to meet the criteria of the noise ordinance for the city within which they are working. Construction outside normal weekday hours (i.e., 7 a.m. to 10 p.m.) would require a noise variance.

Vibration Construction vibrations potentially cause a variety of effects, ranging from influence on vibration-sensitive equipment and potential slight damage to buildings at the highest vibration levels. In most cases, the main concern for construction vibration is potential damage to structures. Most construction processes do not generate vibration levels that approach damage criteria. The thresholds for building damage are one to two orders of magnitude higher (approximately 20 to 40 dB) than criteria for annoyance. Assessment criteria for building damage depend on the type of building construction; assessment criteria for annoyance depend on receptor land use, with the same receptor classifications and criteria as streetcar operational vibration. FTA criteria for assessing building are shown in Table 4.3-12, Lightweight timber buildings are associated with lower building damage thresholds than those built with heavier steel and concrete. While the VdB metric and land use are used for annoyance assessment, the PPV metric and building construction type are used to assess potential building damage.

Table 4.3-12 Construction Vibration Criteria – Building Damage

Building Category PPV (in/sec)a

I. Reinforced concrete, steel or timber (no plaster) 0.5

II. Engineered concrete and masonry (no plaster) 0.3

III. Non engineered timber and masonry 0.2

IV. Buildings extremely susceptible to vibration damage 0.12

Source: FTA Manual, Table 12-3. a in/sec = inch per second



As a basis for calculating vibration levels from construction activities, the FTA Manual includes vibration levels for construction equipment commonly associated with higher levels of vibration. Table 4.3-13 lists project-specific vibration sources for the construction activities anticipated for the LPA.

Table 4.3-13 Construction Vibration Sources

Equipment Levels at 25 feet

PPV (in/sec) VdB

Vibratory Roller 0.210 94 Hoe Ram (hydraulic breaker) 0.089 87 Large Bulldozer 0.089 87 Loaded Trucks 0.076 86 Jackhammer 0.035 79 Source: FTA Manual, Table 12-2.

The susceptibility for damage is based on the building structure, distance from the activity, and the amount of vibration generated by the activity itself. Based on and evaluation of the buildings present along the LPA, building damage due to construction vibration is not anticipated.

Areaways (portions of buildings that are located under the sidewalk) located near the track alignment were also reviewed for potential cosmetic damage from construction vibration. The closest areaways were investigated through photo documentation provided by SDOT. Based on this review, these areaways are most likely associated with Building Category III. There is a possibility of cosmetic damage if the construction equipment listed in Table 4.3-14 are closer to the areaways than the recommended buffer limits.

A significant number of receptors along the LPA alignment are within the vibration impact buffer distances, which indicates the potential for annoyance during construction. Annoyance impacts are estimated at more than 50 percent of all receptors during vibratory roller use and at approximately 25 percent of all receptors during jackhammer use. This type of construction is consistent with roadway improvement and utility projects that have been common in the vicinity.

Table 4.3.14 Construction Vibration Building Damage Impact Buffers

Equipment Building Category

I II III IV

Vibratory roller 14 feet 20 feet 26 feet 36 feet

Hoe ram (hydraulic breaker) 8 feet 11 feet 15 feet 20 feet

Large bulldozer 8 feet 11 feet 15 feet 20 feet

Loaded trucks 7 feet 10 feet 13 feet 18 feet

Jackhammer 4 feet 6 feet 8 feet 11 feet



4.3.4 Mitigation Measures Operation Noise Mitigation. Noise impacts are not anticipated from streetcar operations (steel wheels on rails, crossovers and bells) along the entire Center City Connector alignment. However, noise from streetcar bells at stations will be verified with final operating parameters, and if noise impacts result, SDOT will reduce the bell sound levels, or relocate the bells, to reduce noise to below FTA impact levels.

Operational Vibration Mitigation. Vibration impacts are not anticipated from streetcar operations along the entire Center City Connector alignment; therefore, mitigation is not proposed. The one exception is 401 Terry Avenue, which has existing trackwork and crossover adjacent to the building as part of the South Lake Union Streetcar alignment. The Center City Connector is not expected to increase this existing condition. If determined necessary, SDOT will conduct a more detailed vibration assessment during final design to confirm the results of the initial modeling. If it confirms an existing impact, SDOT will reduce the vibration to acceptable levels by relocating the crossover, using spring-loaded frogs to reduce the gap size between rails, or using resilient track fasteners.

Construction Noise Mitigation. To satisfy SMC for any construction activity, a noise control plan will be developed and implemented to reduce community annoyance. The noise control plan will include, but not be limited to, the following:

Maintain a 1-foot-thick layer of muck or dirt in the bottom of haul truck beds. Use only ambient-sensing broadband back up alarms and minimize backing up. Limit engine idling to 5 minutes or less. Use radios for long-range communication; only use raised voices and public address

systems in an emergency. Use upgraded engine exhaust mufflers, engine shrouds, or sound enclosures on noisier

equipment. Install portable sound barrier around noisier equipment. Use electric and hydraulic equipment instead of diesel or pneumatic equipment. Require the contractor to develop a noise control plan to identify and mitigate noise

impacts based on specific means and methods. Develop noise limits, address complaints, and monitor noise levels during construction. Obtain a noise variance for work performed at night.

Construction Vibration Mitigation. To minimize annoyance from construction-related vibration, SDOT will develop and implement a vibration control plan. The plan requires that the contractor: Select haul routes to avoid areas with higher residential density, as feasible. Phase vibration-producing activities so they do not occur simultaneously, as feasible. Schedule vibration-producing activities outside time periods where nearby buildings are

most sensitive to vibration, as feasible. For example, execute vibration-producing work near residential buildings during daytime hours and commercial buildings during nighttime hours.



Minimize the use of impact tools, such as hoe rams and jackhammers; use lower-vibration equipment, such as concrete saws, for demolishing existing pavement.

Use lower power settings on vibratory rollers or large static rollers, as feasible. Require the contractor to develop a vibration control plan to identify and mitigate

vibration impacts based on specific means and methods. Construction Vibration Mitigation in Areaways. To completely avoid risk of cosmetic damage to areaways, heavy/strong vibratory construction equipment will maintain a buffer from the areaways of 8 feet to 26 feet, such that vibration near areaways do not exceed to 0.2 PPV (inches/second).


4.3 Noise and Vibration - Seattle Streetcar CITY CONNECTOR STREETCAR NOISE AND VIBRATION . ......

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