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Highway Soundwalls

Highway Soundwalls

Metro has a plan to help our communities thrive. It includes creating quieter neighborhoods through our soundwall program for the benefit of LA County residents living in areas of high traffic. 

How is Metro involved with building LA County’s soundwalls?

With the passage of Senate Bill (SB)-45, the California Street and Highway Code was amended to transfer the programming and funding responsibilities of the Post 1989 Soundwall Retrofit Program to Regional Transportation Planning Agencies. In LA County, Metro assumed this responsibility.  However, the eligibility determination as well as design and construction responsibilities for the program remained with the California Department of Transportation (Caltrans). Metro inherited a backlog of soundwall projects totaling nearly $1 billion without any corresponding funding from the state.

What is Metro’s Highway Soundwall Program?

In 2000, the Metro Board of Directors adopted a policy for prioritizing, funding and constructing highway soundwall projects. Metro, in consultation with Caltrans, developed the Retrofit Soundwall List by classifying them in Phases. The soundwalls will be prioritized and delivered in two phases. Phase I consists of soundwalls projects along freeway segments where  where High Occupancy Vehicle Lanes (HOV) were constructed without soundwalls. Phase II consists of all other retrofit/after-the-fact  soundwall locations deemed eligible along various freeways.
There is a possibility that the soundwalls currently on the Retrofit Soundwall List may be constructed out of order as new highway improvement projects are developed (i.e., Express Lanes), as such eligible soundwalls within the limits of those projects will be included in those projects.
Due to a significant backlog and funding limitations, soundwall segments not on the Retrofit Soundwall List are not being initiated at this time. However, Measure R, M, and Local Return revenue funds are allocated to the subregions and cities. Assuming enough Measure R or M funds are available, the cities can work with the subregion to request the allocation of funds to build the soundwall with final approval from the Metro Board.
What is a soundwall and how does it work?
Soundwalls absorb or reflect noise, acting as a barrier between the source of noise such as traffic on a highway) and a sensitive receptor (such as a residential community). Soundwalls are typically built of solid materials, such as concrete, brick and masonry block, and reach between 8 to 16 feet high.
The science behind soundwalls
To identify and validate an eligible soundwall on the highway system, federal and state regulations must be followed and go through a preliminary engineering stage which includes a Project Study Report-Project Report (PSR-PR). The PSR-PR identifies the locations, lengths, and heights of walls, as well as the resulting impacts to the roadway, structures, right-of-way, and the environment. Following approval of the preliminary engineering phase, the project then advances through final design and construction. The final design of a soundwall depends on surrounding topography (for example, hilly or flat land) as well as the location of the homes within the area that qualifies for the soundwall.
Soundwalls can be designed to reflect noise if the impact to the other side does not exceed the threshold for soundwall qualifications and/or there are no sensitive receptors. When reflective soundwalls have noise impacts to the opposing side of the highway, a soundwall can be designed with materials to absorb the sound.  
A general rule to sound is that “if you can see it, you can hear it.” So soundwalls typically must be tall and long enough to block the “line-of-sight” of the highway from the area that it is protecting. This means that soundwalls offer little benefit for homes on a hillside overlooking a highway.

How effective are soundwalls?

The effectiveness of soundwalls depends on the distance between the receptor and the soundwall. For residents located next to a soundwall, the perceived noise level can be cut in half. Soundwall benefits are insignificant at distances greater than 500 feet from the soundwall, typically where traffic noise does not exceed the decibel threshold. 

What are the criteria for a soundwall?

In order for a soundwall to be considered for funding, it must first pass preliminary field tests. The criteria for the field test is summarized below:
  1. Location:  The location is along residential property, parks, churches or other sensitive receptors that exist prior to the construction of a highway or proposed improvements of a highway.
  2. Noise level: The hourly noise levels at the location exceeds a 67-decibel threshold.
  3. Noise reduction: The soundwall will result in a minimum 5-decibel noise reduction
  4. Cost: The soundwall cost is below “reasonable allowance” as calculated using established Caltrans criteria, which is currently $107,000 per benefited dwelling.

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