Because of the ever increasing amount of Noise, Traffic and Pollution generated in Thousand Oaks this page has been divided into several pages;

This web site is now linked to The Noise Pollution Clearinghouse (www.nonoise.org)

Noise Element of the General Plan
(When this is posted on The City of Thousand Oaks web Site we will provide a link to it)

The Noise Element of the Thousand Oaks General plan was adopted and last updated in September of 1987. Currently the Noise Element is going through an update.  Here is where you will find the latest information to help you understand how noise is effecting our community and how the review process is progressing.

SCHEDULE OF THE REVIEW AND APPROVAL PROCESS

CHRONOLOGY OF THE PROCESS

12/17/98  Sound and/or NOISE data was taken at 40 sites through-out the City.  Mr. P. Patrick Mann, AICP, representing, Cotton/Beland/Associates, Inc. the Urban and Environmental Planning Consultants hired by the City to do the study explained the data taken at these sites and answered questions from approximately 25 citizens in attendance.  The data presented showed that the increase in the noise level through-out Thousand Oaks is principally caused by vehicle traffic on freeways and arterial streets in the city.    Individual reports of the data taken at each site was available for review. The next step in the process is the preparation of a preliminary report for review and comments by interested citizens explaining the data and possible mitigation measures.
12/7/98   The Raw Data will be available for review by the Public on December 17th in the City Hall Board Room at 7:00 PM.  
11/6/98    Data from the consultants has been received and meetings will be scheduled in the next few weeks for public review.
10/5/98   Sound level readings were taken throughout Thousand Oaks during September and the first week in October 1998.

INTRODUCTION

Noise has become a key factor in  the perception of  the quality of our environment. Noise effects both the home and work environment, and enjoyment of recreational activity. For these reasons, noise is an important issue in the community planning process.

The State of California has mandated that each county and city prepare a noise element as part of its general  plan. California Government Code, Division 1, Planning and Zoning, Chapter 3, Local Planning, Article 5, Section 65302(f) requires a plan including:

"A noise element which shall identify and appraise noise problems in the community. The noise element shall recognize the guidelines established by the Office of Noise Control in the State Department of  Health Services and shall analyze and quantify, to the extent practicable, as determined by the legislative body, current and projected noise levels for all of the following sources:

1. Highways and freeways.
2. Primary arterials and major local streets.
3. Passenger and freight on-line railroad operations and ground rapid transit systems.
4. Commercial, general aviation, heliport, helistop, and military airport operations, aircraft overflights, jet engine test stands, and all other ground facilities and maintenance functions related to airport operation.
5. Local industrial plants, including, but not limited to, railroad classification yards.
6. Other ground stationary noise sources identified by local agencies as contributing to the community noise environment."

Department of Housing and Urban Development (HUD)

HUD's overall goal is for exterior residential noise levels not to exceed 55dB Ldn and for interior noise levels not to exceed 45 dB Ldn.

a) Exterior sound levels of 65 dB Ldn and below are acceptable and allowable.
b) Projects within 65 to 75 dB Ldn require special environmental clearance and additional noise insulation.
c) Projects with a 75 dB and greater require a submittal of an Environmental Impact Statement (EIS).

DEFINITIONS

Decibel (dB) - A decibel is the unit for measuring sound pressure level and is equal to 10 times the logarithm (to the base 10) of the ratio of the measured sound pressure squared to a reference pressure (i.e. 20 micro-pascals) squared. More simply put, decibels are measured in a similar manner to the Richter scale which measures the magnitude of earthquakes.

What does all this mean? Well as explained best by Don & Carolyn Davis in their Sound System Engineering text;  The decibel is 1/10 of a bel. (The bel is named in honor of Alexander Graham Bell.) Since all decibel notation systems are based on logarithms, we can start with a review of basic logarithmic theory.

Our human senses - touch, sight, hearing, sense of weight, etc. - all function logarithmically. That is, in the presence of a stimulus the least perceptible change is proportional to the already existing stimulus. Humanly perceived equal ratios seem to be equal increments.

The sensitivities of the various senses are not the same. Typical differences are:

Sensitivity to light-intensity changes: 1% = 0.087 dB

Sensitivity to change in the length of a line: 2% = 0.176 dB

Sensitivity to change in a felling of weight: 10% = 0.915 dB

Sensitivity to change in sound loudness: 30% = 3 dB

A-Weighted Sound Level (dB(A)) - An A-weighted sound level is the sound pressure level in decibels as measured on a sound meter using the a-weighted filter network. The A-weighting filter de-emphasizes the very low and very high frequency components of the sound in a manner similar to the response of the human ear and provides good correlation with subjective reactions to noise.

Community Noise Equivalent Level (CNEL) - A CNEL is the average equivalent A-weighted sound level during a 24-hour day, obtained after addition of five decibels to sound levels occurring during the evening from 7 p.m. to 10 p.m. and addition of ten decibels to sound levels occurring during the night from 10 p.m. to 7 a.m.  The 5 and 10 decibel penalties are applied to account for increased noise sensitivity during the evening and nighttime hours. The CNEL represents the daily energy noise exposure averaged on an annual basis. It is not measured, but computed. The State of California uses the dB CNEL noise index to relate community noise exposure to compatibility criteria, Typically, minor roadways do not generate sufficient noise to create a 65 dB CNEL value off the roadway while major arterials and freeways can create 65 dB CNEL values extending hundreds of feet into adjacent properties.

Day-Night Average Level (Ldn) - The average equivalent A-weighted sound level during a 24-hour day, obtained after addition of ten decibels to sound levels during the night time from 10 p.m. to 7 a.m. The 10 decibel penalty is applied to account for increased noise sensitivity during the nighttime hours. The Ldn represents the daily energy noise exposure averaged on an annual basis. Where evening sound levels are not substantial, an Ldn value is generally within 2 dB of a CNEL value. However, where loud events occur between 7 p.m. to 10 p.m., such as a go-cart or outdoor concert facility, an Ldn value could be well below a CNEL value that applies a 5 dB penalty to that time period.

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