Paul M. Kohler Noise Abatement Program Manager

DULLES CONNCECTOR ROADSOUND WALL PROJECT

FUNDAMENTALS OF TRAFFIC NOISE AND RESULTS

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WHAT IS NOISE?

• Noise is unwanted sound.• It is perceived differently by every person.• Can be irritating to one person may be

tolerant to another.• Sound is transmitted by pressure variations in

the air from its source.• Most sound sources are characterized as a

point or lines sources.

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POINT vs. LINE SOURCE

• A point source occurs when a sound source is stationary (e.g. a horn).

• Sound radiates equally in all directions.• Noise levels for a point source decreases by 6

decibels per doubling of distance.

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POINT vs. LINE SOURCE

• A line source when many source are moving in a line (e.g. traffic noise).

• Noise levels for a line source decreases by 3 decibels per doubling of distance.– Example: If you experience 60 decibels at 50 feet then

you would experience 57 decibels at 100 feet.

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• Noise is measured in decibels on a logarithmic scale. This scale does not work the same way as most other familiar scales.

THE DECIBEL

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THE DECIBEL

≠ 279 dB

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• An increase in 10 decibels is considered as twice as loud to the average listener.

THE DECIBEL

Physical Noise vs. Perceived NoiseActual Sound Level

ChangePerceived Sound Level

Change+20 dBA Four times as loud

+10 dBA Twice as loud

+5 dBA Readily perceptible

+3 dBA Barely perceptible

0 dBA Reference level

-3 dBA Barely perceptible-5 dBA Readily perceptible

-10 dBA Half as loud

-20 dBA One quarter as loud

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• Doubling of the sound source causes noise levels to increase by 3 decibels.

THE DECIBEL

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THE DECIBEL

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THE DECIBEL

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THE DECIBEL

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THE DECIBEL

• Community of practice among Federal and State DOTs is to use a noise level impact threshold associated with interference of speech communication.

• Annoyance, sleep and task interference is not practicable since noise is perceived differently by every person.

• 67 decibels is considered to be impacting normal speech at a 3-foot distance.

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THE DECIBEL

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• Traffic Noise Model 2.5 (TNM)• TNM used to predict and assess noise

levels in future (design) year. • TNM went through an extensive

validation effort to ensure its accuracy.• April 14, 2004 FHWA mandated the use of

TNM.

THE NOISE MODEL

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• Noise Model Inputs– Noise Sensitive Receptors– Proposed design alternative– Traffic (volume, speed,

composition)– Propagation Features

(Cut/Fill Lines, Building Rows, Ground Zones, etc.)

– Existing or Proposed Barriers

THE NOISE MODEL

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• Noise Model Results– Noise levels (existing, design

year, mitigated)– Barrier design information

THE NOISE MODEL

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MITIGATION

• Primary consideration given to reduce traffic noise impacts to the nearest exterior ground level area of frequent human use.

• Sound walls can be effective in mitigating traffic noise for receptors within 200 feet of a highway.

• Sound walls will not totally eliminate traffic noise.

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MITIGATION

• Where do we place the sound wall?– Between the source and the receiver.

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MITIGATION• Is there an optimal location?

– Yes but it depends on the terrain, existing utilities, and structures (bridges, signs and culverts) which is balanced among these variables.

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MITIGATION

• How high should we design the wall?– That depends on where noise impacts occur.– Was the line of sight broken?

Noise Analysis Results

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• 600 locations within 1000 ft of Dulles Connector Road modeled for computed loudest hour in 2032 Future Conditions.

• 267 locations representing adjoining residential properties were reported

• 46 residential properties are predicted to have future noise levels of 66 dBA or more.

• Sound wall heights at intervals of 10, 12, and 14 feet were evaluated for noise reduction effectiveness for the full length of the Dulles Connector Road.

• A 10-ft sound wall will mitigate future noise levels for the majority of residential properties along the north and south sides of the highway.

• A 14-ft sound wall is needed near the I-66 off ramp to the Dulles Connector Road.

Noise Analysis Results

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• Existing noise levels range from: 47 dBA to 68 dBA.

• Design year noise levels (without wooden walls) range from: 50 dBA to 73 dBA.

• Design year noise levels (with sound wall) range from: 47 dBA to 66 dBA.

• Noise reductions range from: 0 dBA to 10 dBA.

• Individual results located on the display boards.

John C. MuseDistrict Environmental Manager

DULLES CONNCECTOR ROADSOUND WALL PROJECT

FUNDAMENTALS OF TRAFFIC NOISE AND RESULTS

Project Purpose

Chapter 874 Virginia Acts of Assembly 2010: “Pursuant to the provisions of the Memorandum of Agreement between the Commonwealth of Virginia Department of Transportation and the Metropolitan Washington Airports Authority, in conjunction with the construction of rail mass transit in the right of way of the Dulles Access/Toll Road Connector (DATRC), sound walls shall be constructed along residential properties from the beginning of the DATRC to Interstate Route 66 with funding from the Commonwealth Transportation Fund."

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Project Guidelines

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• Reduce future noise levels below FHWA* standard of 67 decibels.

• Compute the future year 2032 rail noise levels and integrate data into Traffic Noise Model.

• Model existing and future (year 2032) noise levels without existing wood barriers.

• Compute loudest hour noise levels at nearest exterior ground level area of frequent human use.

• Evaluate sound wall heights for most effective mitigation of future noise level increases.

• Construct sound walls along both sides of the highway within existing right-of-way.*Federal Highway Administration, 23 CFR Part 772 Table 1 – Noise Abatement Criteria for Activity Category B (July revision)

Project Development

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• Final Noise Analysis and Sound Wall Design underway.

• Identifying conflicts & adjust sound wall alignment to avoid.

• Ongoing coordination with utilities and Dulles Rail Project.

• Design approval: May 2012• Advertise project: November 2012.• Begin construction: Early Spring 2013.

Questions & Comments

1. Place Comment Sheet tonight in Comment Box.or

2. Mail your Comment Sheet to VDOT.or

3. Email to meeting_comments@vdot.virginia.gov; please reference “Sound Walls Comment” in thesubject line.

Your comments would be appreciated byDecember 27, 2011

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DULLES CONNCECTOR ROADSOUND WALL PROJECT

FUNDAMENTALS OF TRAFFIC NOISE AND RESULTS