Indicator ES.5.a Average daytime and nighttime outdoor noise levels
Data Source
Seto, Holt and Rivard. University of California, Berkeley and SF Department of Public Health, Environmental Health Section. Traffic Induced Noise: Developing Analytic Tools for Assessing the Impacts of Transportation Policy on Environmental Health.
Map prepared by City and County of San Francisco, Department of Public Health, Environmental Health Section using ArcGIS software.
Table data is presented by planning neighborhood. Detailed information regarding geographic units of analysis, their definitions, and their boundaries can be found in the HDMT at the following links:
http://www.thehdmt.org/etc/Geographic_Units_of_Analysis.September_2009.pdf
http://www.thehdmt.org/data_map_methods.php
Explanation and Limitations
The Decibel (dB) is a unit of measurement used to quantify the intensity or magnitude of sound. A 10 dB change is generally perceived by the human ear as a doubling of noise. The LDN (Level Day/Night) noise level averages the daytime and nighttime noise levels (logarithmically) over a 24-hour period and includes a 10 dB (penalty) added to the nighttime noise level (10 pm to 7 am).
The map illustrate 24-hour noise levels in San Francisco modeled using the Federal Highway Administration's Traffic Noise Model and based on local traffic count data. In addition, remote sensing data were used to estimate neighborhood-specific percentages of different types of vehicles on arterial versus non-arterial streets. Noise levels were measured directly on 218 streets and compared against modeled levels for validation. Field measurements are combined with noise modeling software to quantify noise levels in SF communities with special emphasis on understanding the effects of traffic volumes on the acoustical environment. Data assists with implementation of State Building Code requirements for acoustical insulation of new residential construction. The San Francisco Noise Model results can help community groups advocate for sound walls, less mechanical equipment, less trucks, and quieter buses
Multiple other factors influence the levels of noise in a neighborhood including topography, wind patterns, the density and type of traffic at different hours throughout the day and night, the presence or lack of trees, sound barrier walls and other noise obstructions, stationary sources of noise, the height and density of housing, etc.
The San Francisco Noise Control Ordinance, Article 29, San Francisco Police Code provides an acoustical safety net for those noise sources that cannot be minimized through informed planning. It is an unfortunate fact of urban life that oftentimes what is seen as progress and development results in the degradation of the acoustical environment. Increasing truck and automobile traffic elevates the ambient street noise, while expanded use of air conditioning invades the quiet of neighborhood backyard. The rear yards of San Francisco often function as acoustical sanctuaries from the urban turmoil. It is important to protect them from the intrusion of new and unnecessary noise sources.
Why is this a Community Health Indicator?
The health impacts of environmental noise depend on the intensity of noise, on the duration of exposure, and the context of exposure. The Environmental Protection Agency identifies a 24-hour exposure level of 70 decibels as the level of environmental noise which will prevent any measurable hearing loss over a lifetime.
Noise levels of 55 decibels outdoors and 45 decibels indoors are identified as preventing activity interference and annoyance. These levels of noise are considered those which will permit spoken conversation and other activities such as sleeping, working and recreation, which are part of the daily human condition. Source: Environmental Protection Agency, http://www.epa.gov/history/topics/noise/01.htm Long term exposure to moderate levels of environmental noise can adversely affect sleep, school and work performance, and cardiovascular disease.a
Noise affects sleep both by waking people up and reducing the quality of sleep. According to the World Health Organization, reductions of noise by 6-14 dBA result in subjective and objective improvements in sleep. Environmental noise is a risk factor for cardiovascular disease. Chronic road noise can affect cognitive performance of children including difficulty keeping attention, concentrating and remembering, poorer reading ability, and poorer discrimination between sounds.b The combination of noise and poor quality housing can have additive effects. In one study, a combination of these factors was associated with higher stress and stress hormone levels.c
A comprehensive synthesis of the noise heath effects and control is contained in the World Health Organization's Guidelines for Community Noise available at: http://www.who.int/docstore/peh/noise/guidelines2.html
- Dora C, Phillips M, eds. Transport, environment and health. WHO Regional Publications, European Series, No. 89. 1999. http://www.euro.who.int/document/e72015.pdf
- Noise and Health: Making the Link. London Health Commission, 2003. http://www.londonshealth.gov.uk/pdf/noise_links.pdf
- Evans G, Marcynyszyn LA. Environmental Justice, Cumulative Environmental Risk, and Health among Low- and Middle-Income Children in Upstate New York. Am J Pub Health 2004;94:1942-1944.