DelDOT's Noise Abatement Policy is based on Federal Highway Administration (FHWA) regulations. The Delaware Department of Transportation (DelDOT) first established a policy in 1993 to lessen the impact of highway traffic noise on people in neighborhoods and in other noise-sensitive areas, such as churches, schools, hospitals and certain public recreational areas. The policy was revised in 2011 and updated in 2020 in response to changes to federal regulations. This webpage explains how DelDOT carries out its noise reduction program. It also details the conditions that must be present for DelDOT to implement noise abatement measures on highway projects and lists ways to learn more about highway noise control regulations and policy.
What is Noise Abatement?
Noise abatement is any measure, practice, or action that reduces noise emanating from highways as heard at specific locations that would be sensitive to highway noise. It usually involves multiple strategies to dampen and deflect noise away from sensitive locations. Much can be accomplished by the careful location and alignment of the highway and use of surrounding topography. Traffic management measures including, but not limited to, traffic control devices and signing for prohibition of certain vehicle types, time-use restrictions for certain vehicle types, modified speed limits, and exclusive lane designations may be considered. Physical barriers that shield sensitive locations are used when other methods are not available.
When does DelDOT conduct highway traffic noise studies?
DelDOT conducts studies and evaluates options for reducing noise levels along proposed federally funded highway improvement projects. These projects must meet one of the following conditions:
- highway is being built on a new location;
- An existing highway is being redesigned with a significant change in its alignment (horizontal or vertical); or
- The number of through traffic lanes on an existing highway is being increased.
How is noise impact determined?
Engineers use computer models to analyze and predict noise levels based on the loudest hour of the day for future conditions. They also measure existing noise levels in various locations along the proposed highway project when there is no existing roadway to use for the computer models. Along with the road's design, they must consider the area's topography, the distance between the road and nearby properties, traffic speeds and the sounds created by different types of vehicles. Using that data, the computer model predicts the future noise level, which is compared with FHWA and DelDOT noise criteria. If this comparison identifies an impact, DelDOT engineers must investigate noise reduction options.
Noise along Existing Highways
DelDOT does not do stand-alone noise abatement projects along existing highways. DelDOT studied the feasibility of installing noise walls along existing highways at the request of the Delaware General Assembly (Section 114, FY 2000 Bond Bill). DelDOT reported its findings in June 2001. In that report, DelDOT identified several existing locations that exceeded threshold levels of traffic noise that could warrant implementation of noise abatement measures. However, the cost to implement such abatement was not deemed reasonable and the Delaware Legislature did not support funding a program to implement noise walls on existing highways.
Noise Complaints at specific locations
DelDOT has the ability to use specialized consultants to study the noise characteristics at specific locations. Such studies are based on citizen complaints usually in anticipation of a new land use or subdivision. Such concerns should be directed to DelDOT's Subdivision Section in the Division of Planning for their consideration. Keep in mind, however, DelDOT does not do stand-alone noise abatement projects along existing highways. The Subdivision Section may be able to incorporate noise abatement measures as a permit condition on developer's plans as land uses change in the future.
How can highway traffic noise be reduced?
Several options are available. First, DelDOT engineers try to reduce the anticipated noise while they are designing the road by shifting the road away from the affected properties. They also consider reducing the speed limit, or designing the road so its surface is lower through the affected area creating a natural sound barrier, or other traffic management measures. Another option is the use of earthen berms to block the noise. If designing the road differently is not possible, DelDOT engineers then consider noise walls. The walls can reduce traffic noise significantly and improve quality of life for people living behind them.
Will trees and fencing provide noise abatement?
While trees and fences offer privacy and can be aesthetically pleasing, they do little to actually reduce roadway noise. As such, DelDOT cannot take credit for them as noise abatement. However, landscaping is often a component of our roadway plans. Property owner sentiment will always be a consideration in decisions regarding the inclusion of landscaping features in our projects.
What is a noise wall?
It is a specially designed structure built to reduce noise levels created by nearby highway traffic. It is built only after noise impact studies are conducted and certain conditions are met.
How are noise walls funded?
They are paid using a mix of funds, but the primary share is federal and set at the federal participation rate for the project. On many projects this amounts to 80 percent of the cost of the noise wall. The remaining 20 percent matching funds come from State sources. Federal funding must be present for noise abatement to be considered.
When is a noise wall considered reasonable?
Noise walls must meet the following conditions in order to be considered reasonable and therefore eligible for federal funding:
- They must not be opposed by a majority of the community the noise wall is intended to protect;
- They must reduce noise levels by at least 9 decibels for at least 25 percent of the properties that the noise wall is intended to protect; and
- They must cost less than $30,000 per affected property
What if the cost is more than $30,000 per affected property?
If the cost of noise wall construction is more than $30,000 per affected property, it is considered an unreasonable expense. Under federal regulations a third party contributor cannot make up the difference. Doing so would result in the expenditure of public tax dollars on something that is already deemed unreasonable. It also poses equity concerns that might result if only those communities with the ability to cost share could get noise abatement while less fortunate communities would go without.
Third party funding would only be acceptable in order to make functional enhancements, such as absorptive treatment and access doors or aesthetic enhancements, to a noise abatement measure already determined to be feasible and reasonable.
What will the noise walls look like?
Noise walls come in various materials, textures, colors and finishes. The goal is to select an attractive design that blends well with its surroundings. A consistent appearance is also one of the main considerations when the walls are to be used in a long corridor.
DelDOT does not have a standard aesthetic treatment for noise walls. The design of the noise wall will be chosen based on the context of its surroundings, type of noise environment, sound wall manufacturing capabilities and engineering costs. Public input is sought from affected citizens and local governments about the walls' color and finish during DelDOT public workshops. These workshops are held periodically as construction plans for a project are developed.
Who maintains noise walls?
Noise walls built on State rights of way are maintained and repaired by DelDOT.