Noise walls cannot be built by request as FTE and the Florida Department of Transportation do not have programs to “retrofit” existing highways. The decision to analyze noise abatement starts in the planning phase when there are plans to widen a roadway, change the alignment of a roadway, or build a new roadway. Noise walls are built to reduce noise under future conditions based on impacts that may occur from these types of roadway modifications.
Residential buildings that existed or had a building permit before the Date of Public Knowledgewill be considered for noise abatement through all phases of the project. Any residences that receive a building permit after the Date of Public Knowledge will not be considered for noise abatement in future phases of the project.
The noise walls near your house may be on the shoulder and the noise walls on the other side of the highway may be near the edge of the right-of-way (FDOT property). Both systems are effective and are modeled with a computer model to ensure they provide the greatest benefit for impacted residences by reducing noise levels. Noise walls are most effective either near the receiver (residential or other qualifying category) of the noise or near the source of the noise. Noise walls that are built near the right-of-way line (near the residences) need to be tall since noise spreads as it travels. Noise walls near the source of the sound (traffic) can be shorter since the sound doesn’t travel as far before it meets the noise wall. Noise walls at the right-of-way line can be built as high as 22-feet, however, noise walls on the shoulder are limited to 14-feet, and only 8-feet on structures such as bridges and on top of embankment walls. Some restrictions such as drainage canals, underground utilities, or other engineering constraints dictate the type of noise wall that can be built.
When a noise study is performed to predict future noise levels, features such as berms and neighborhood privacy walls located on private property are put into the computer traffic noise model. These features can reduce noise to a level that is under the noise level that is considered impacted. So, adding a second wall on the roadway side would either not be warranted because there are no impacts, or would not provide an additional noise reduction that would be reasonable to construct a noise wall (meet FDOT criteria).
Noise walls do not eliminate traffic noise. They are designed to reduce traffic noise for residences that are impacted by traffic noise. A residence is considered impacted if future traffic noise is predicted to reach 66 dB(A) (decibels in the A-weighted scale) or above (averaged over a one-hour period) for the future design year of the project. A residence is considered benefited if they receive a 5 dB(A) reduction in traffic noise from the noise wall. Noise walls are most effective for residences that are closest to the noise wall. The benefit decreases the farther the residence is from the noise wall. However, the level of traffic noise also decreases the farther the residence is from the noise wall. So, a residence three rows away from the highway will receive little benefit from a noise wall, but will also be receiving less traffic noise from the highway and may not be impacted according to the Federal Highway Administration (FHWA) and state regulations. The video above provides more information about these concepts.
Trees provide a psychological effect on noise; if you can’t see it, you won’t be bothered by it as much. However, they provide little to no actual noise reduction and under FDOT policy, vegetation is not considered a noise abatement measure. In order for trees to provide a reduction in sound, they need to be tall, dense enough that you cannot see through them, and about 100-feet deep between the roadway and the residence. Sometimes FTE or other entities must remove trees within our right-of-way or in adjacent right-of-way. Also, there are other times where a utility company may remove trees on their right-of-way. Changes in landscaping alone do not qualify for noise walls to be constructed. Landscaping is considered for each project and usually a landscaping project is done after completion of roadway construction. Any landscaping questions should be directed to the Project Manager.
There are many reasons for this. Some neighborhoods have existing berms and privacy walls that reduce noise. Other neighborhoods are set back so that there are few to no impacted residences (residences who will experience future traffic noise at or higher than 66 dB(A) averaged over a one-hour period). In some cases, it is because the cost per benefited residence exceeds the FHWA and FDOT threshold. If the cost of the noise wall is greater than the cost per benefited residence, currently $42,000 per benefited residence, the wall is not considered reasonable. Dense neighborhoods have a greater chance of being cost effective than neighborhoods with large tracts of land for each house.