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How do sound walls and sound blankets work to reduce noise at a construction site?

During any construction project, it can be expected that some activities are noisier than others, which can be disruptive to the community.

The Metro Purple Line Extension Project has implemented several construction noise mitigation efforts in order to help reduce the noise caused during construction work. These include creating sound walls at staging yards, using moveable sound blankets at construction sites, configuring construction sites and equipment so as to minimize noise impacts on the community, and phasing activities to avoid simultaneous activities that generate high noise levels.

Stationary and moveable sound barriers are built with noise-absorbing material at least two inches thick that help reduce the overall noise levels to adjacent areas. See figure below. According to Michelle Marquez-Riley, environmental specialist for the Purple Line Extension Project, “A 5-10 dBA noise reduction is achievable with these barriers which both are designed to block and absorb noise.”

Currently, there are 20-foot noise barrier walls that surround the Crenshaw Staging Yard, which have effectively kept construction noise down to allowable city-enforced threshold levels while the yard is used by contractors. Sound walls will be custom built at every staging yard for the project following an acoustical analysis of proposed construction activities, equipment and schedule for each yard to determine an effective height.

Moveable sound blankets are the most effective when they are close to the noise source and flush or overlapped to close any gaps between barrier units.  The materials in the blanket reduce the reflection of sound waves from the construction site. Moveable sound barriers have been used throughout the project during advanced utility relocation work, including portable “huts” covered in sound blankets as shown in the photos.

Metro continually monitors ongoing construction activities to ensure that applied noise mitigation measures are effective and within allowable noise levels.  Additionally, regular noise awareness training sessions are held to ensure that all project staff, inspectors, contractors and third party utility companies maintain a responsibility as stewards to the surrounding communities.