NOISE ABATEMENT TEAM - OFFICE OF ENVIRONMENTAL DESIGNCITIZENS'CORRESPONDENCE - M-Z 2002

Oct 6, 2026

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Follow-up correspondence addressing a citizen request for the State’s Sound Barrier Policy and for noise level measurement results for the Parkwood community along the outer loop of I-495 west of Cedar Lane in Montgomery County. The letter explains Type II sound barrier criteria, when barriers are not constructed, and possible non-noise-reducing visual alternatives. It summarizes worst-case noise measurements, barrier effectiveness by receptor distance and geometry, and supplemental computer modeling separating contributions from I-495 and Cedar Lane traffic.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages618

Reading Time25 h 57 min

AccessFree to download

Noise Barrier Policy Follow-up

Type II sound barrier alternatives

Exhibit 1: Noise level measurements (worst-case)

Exhibit 2: Barrier study results and effectiveness factors

Exhibit 3: Required barrier extent

Exhibit 4: Supplemental computer modeling and traffic contributions

9 # NOISE ABATEMENT TEAMOFFICE OF ENVIRONMENTAL DESIGNCITIZENS'CORRESPONDENCE M-Z 2002 JANUARY THRU DECEMBER ameGs'CDQpr(ONOB Y M- E 2002 Maryland Department of TransportationState Highway Administration October 1,2002 Mr.Gerald Madden9604 Cedar LaneBethesda MD 20814-4046 Dear Mr.Madden: This letter is a follow-up to your recent e-mail message requesting a copy of the State's SoundBarrier Policy and the results of the noise level measurements taken in the Parkwood community alongthe outer loop of I495 west of Cedar Lane in Montgomery County.I appreciate the opportunity torespond to your inquiry. As you requested,enclosed is a copy of the State's Sound Barrier Policy that went into effectMay 11,1998.You asked what alternatives are available in the event that a barrier is not effective.ForType II sound barriers,if the noise level analysis and the associated sound barrier analysis determine thata sound barrier willnot be effective,the sound barrier will not be constructed.The goal of the Type Ⅱsound barrier program is to reduce the highway traffic noise levels in the outdoor living space of theresidence.In the case where construction of a sound barrier has been determined to not be feasible andthe community meets allof the other required technical criteria,SHA has considered the installation oflandscape screening or privacy fencing.These measures are used to provide a visual barrier but not onethat would reduce the highway traffic noise levels. Enclosed,also,is detailed information on the sound barrier evaluation for the Parkwoodcommunity.Six enclosures are labeled“Exhibit I”through “Exhibit 4”and will be discussed in detail.Exhibit 1 summarizes the noise level measurements that were conducted in the Spring of 2000.Themeasurement study included measuring of noise levels over 24-hour periods and also for short-term(asshort as ten minutes)intervals.The results shown in Exhibit I represent the “worst-case”(highest)noiselevels measuredat the various listed receptor locations.Four residences (shaded portion of the table)were found to have noise levels at or above the 66 decibel impact threshold. Exhibit 2 summarizes the results of the sound barrier study,including the dimensions andanticipated effectiveness of a barrier system for the four residences identified as “impacted”in Exhibit 1.This data was also summarized in our February 26,2002 letter to you.These impacted homes are theclosest to I-495 along Parkwood Drive near the intersection at Cedar Lane(approximately 500 to 550 feetfrom the highway).Sound barriers are most effective for receivers in the areas immediately adjacent tothem.As the distance away from the barrier of a given height increases,the amount of noise reductiondecreases.For this reason,distant receivers such as those along Parkwood Drive would experiencelimited benefits from a sound barrier placed along I-495,unless the barrier is:1)very all;and 2)extendsa substantial distance along the highway. 2 Parris N.GlendeningGovernorJohn D.PorcariSecretaryParker F.WilliamsAdministrator Mr.Gerald Madden Page Two Basic noise reduction principles can be explained by the two enclosed illustrations,labeledExhibit 2a and Exhibit 2b.Of particular interest is the bottom illustration on Exhibit 2a.The amount ofnoise reduction by a barrier is related to the extra distance that sound must travel up and over the barrier(the diffracted path)when compared to the direct path.With a "typical"receiver close behind the barrier,the relative difference in the two paths is greater than for more distant receivers.The other factoraffecting distant receivers is illustrated in Exhibit 2b.The greater the distance behind the barrier thesmaller the angle of coverage and thus,the smaller the noise reduction.The only way to increase thenoise reduction is to lengthen the barrier along the roadway,thereby increasing the angle of coverage.This ultimately translates into a substantial increase in cost of the barrier sy

FAQs

What information was requested and provided in the follow-up letter?

The letter follows up on an e-mail requesting the State’s Sound Barrier Policy and results of noise level measurements for Parkwood along I-495 west of Cedar Lane. The enclosure includes the policy and detailed evaluation information.

Under what conditions would a Type II sound barrier not be constructed?

If noise level analysis and the associated sound barrier analysis determine a barrier will not be effective, the sound barrier will not be constructed.

Why is noise reduction limited for distant receivers such as those along Parkwood Drive?

As distance from the barrier increases, noise reduction decreases due to reduced coverage angle and changes in the diffracted path difference compared with the direct path. Increasing reduction would require lengthening the barrier along the roadway, increasing cost.

Oct 6, 2026

Uploaded by Đào