Chapter 12 - Noise

What does this topic include?

This chapter provides an overview of the Department's noise policies and procedures as they relate to transportation project planning and delivery. Information is provided to give the reader a basic understanding of noise impacts, the evaluation of potential abatement measures, and documentation requirements. NOTE: The information in this chapter is based on the 2020 Traffic Noise Analysis Protocol (PDF). Projects that do not have a completed noise study signed and approved by the Department (or FHWA for non-assigned projects) by July 13, 2011, will be required to comply with the 2020 Protocol and the revised regulations. If a project is modified such that a NEPA reevaluation and new noise study report are required, the Protocol and regulations in place at the time of the reevaluation must be used.

Decision Tree - Preliminary Noise Abatement (23 CFR 772)

This decision tree provides information about preliminary noise abatement.

Laws, Regulations, and Guidance

See also SER Volume 1, Chapter 1, "Federal Requirements," Chapter 2, "State Requirements," and Chapter 38, "NEPA Assignment."

Federal Laws and Regulations

State Laws and Regulations


Policy Memos

  • Policy and Protocols Related to Noise Studies (PDF), Katrina C. Pierce (June 30, 2015). If a new Noise Study Report becomes necessary, noise barrier commitments made under older Protocols will be honored if there are no significant project design changes which would impact the proposed barrier(s).
  • Standardization of Noise Reports, Gary R. Winters (July 24, 2002)

Further Reference

The following documents are available from the FHWA Highway Traffic Noise Website:

The Federal Noise Analysis

For a federal or Federal-aid project, the noise technical report and the noise section of the environmental document must reflect the following basic analytical steps for all alternatives:

  • Is the project a Type I project?
  • If the project is a Type I project, would the project result in a traffic noise impact?
  • If the project would result in a traffic noise impact, noise abatement must be considered.
  • Is the noise abatement that is considered reasonable and feasible?

Type I Projects

A Type I project as defined in 23 Code of Federal Regulations (CFR) 772, is a federal or Federal-aid project for:

  1. The construction of a highway on a new location; or
  2. The physical alteration of an existing highway where there is either:
    1. Substantial horizontal alteration. A project that halves the distance between the traffic noise source and the closest receptor between the existing condition to the future build condition; or
    2. Substantial vertical alteration. A project that removes shielding thereby exposing the line-of-sight between the receptor and the traffic noise source. This is done by altering either the vertical alignment of the highway or the topography between the highway traffic noise source and the receptor; or
  3. The addition of a through-traffic lane(s). This includes the addition of a through-traffic lane that functions as a high-occupancy vehicle (HOV) lane, high-occupancy toll (HOT) lane, bus lane, or truck climbing lane; or
  4. The addition of an auxiliary lane, except for when the auxiliary lane is a turn lane; or
  5. The addition or relocation of interchange lanes or ramps added to a quadrant to complete an existing partial interchange; or
  6. Restriping existing pavement for the purpose of adding a through traffic lane or an auxiliary lane; or
  7. The addition of a new or substantial alteration of a weigh station, rest stop, ride-share lot, or toll plaza.

The Department uses this same definition when evaluating State Highway System (SHS) projects without federal funding.

For local agency Federal-aid transportation projects "off" the (SHS) (Local Assistance projects) the determination as to whether or not a project is a Type I Project and the decision to prepare a Noise Study (NSR), is made during completion of the Preliminary Environmental Study (PES) form. Instructions for determining Type I Projects are provided in the Local Assistance Procedures Manual, Chapter 6, Exhibit B, #3 and 4.

When Does a Project Result in a Noise Impact that Requires Consideration of Abatement?

After the determination is made that the project is a Type I project, the next step in the analysis is to determine whether the project would result in a noise impact that requires consideration of noise abatement. To make this determination, several steps must be taken:

1. Identify Land Uses in the Project Area - Identify existing land uses in the project area and identify the appropriate Activity Category as defined in 23 CFR 772 for each land use type. Include undeveloped land for which a building permit has been issued.

2. Determine Existing Noise Levels at Receptors - Existing noise levels are determined based on noise monitoring. The Technical Noise Supplement (TeNS) provides information on how to conduct noise measurements for this purpose. Also, the Caltrans Division of Environmental Analysis - Noise and Vibration Studies office provides online training on measurements and instrumentation.

3. Model Future Noise Levels with the Project - Currently, the FHWA Traffic Noise Model (TNM) 2.5 Program  is the modeling software required by FHWA for traffic noise studies. The TNM predicts traffic noise levels based on projected worst hour traffic volume (the traffic volume and speed conditions that produce the highest hourly noise level), traffic mix (percentage of truck traffic), ground type, and the distance between projected traffic and of the receptors.

4. Determine if Traffic Noise Impacts are Identified - A noise impact occurs when: 1) there is a substantial noise increase between design-year build conditions and existing conditions or; 2) the design-year build traffic noise level approaches or exceeds the FHWA noise abatement criteria (NAC). Section 3 of the Caltrans Traffic Noise Analysis Protocol (Noise Protocol) provides more specific definitions of these impact types:

  • Substantial Increase - A noise increase is substantial when the predicted noise level in the design-year with the project exceeds existing noise levels by 12 dBA or more.
  • Approach or Exceed the Noise Abatement Criteria (NAC) - The NAC for a receptor is based on its land use type (see the Noise Protocol). The Protocol defines "approach" as being within 1 dBA of the NAC. For example, if the NAC is 67 dBA, a predicted noise level of 66 dBA is considered to "approach" the NAC.
  • More detailed information on NAC can be found at FHWA's Highway Traffic Noise webpage.

Noise Abatement Considerations

If traffic noise impacts are predicted, noise abatement measures must be considered and evaluated. Preliminary noise abatement design includes considerations such as barrier heights, lengths, and location (see TeNS Section 5 for additional details). Noise abatement is only considered where frequent human use occurs and a lowered noise level would be of benefit.

Determining Whether the Proposed Abatement is Reasonable and Feasible

Noise abatement will be included as part of the project only if constructing the abatement is reasonable and feasible. Feasibility is an engineering consideration and includes factors such as access requirements for driveways, topography, presence of underground and above ground utilities, and safety. Noise abatement must be predicted to reduce noise by at least 5 dB at an impacted receptor to be considered feasible from an acoustical perspective.

The overall reasonableness of noise abatement is determined by the following three factors:

  • the noise reduction design goal (7 dB for at least one or more receptors),
  • the cost of noise abatement, and
  • the viewpoints of benefited receptors (including property owners and residents of the benefited receptors).
Section 3 of the Noise Protocol provides details on how these factors are to be assessed.

Noise Analysis Under the California Environmental Quality Act (CEQA)

Noise analysis for projects under CEQA centers on whether the project or the proposed noise abatement would result in significant adverse environmental effects. Whether an increase in future noise level would result in a significant effect for purposes of CEQA is determined by comparing the existing noise level (or baseline environmental setting) to the predicted noise level with project. The CEQA noise analysis is completely independent of the 23 CFR 772 noise analysis, which is centered on noise abatement criteria. Under CEQA, the assessment entails looking at the setting of the noise impact and then how large or perceptible any noise increase would be in the given area. Key considerations include: the uniqueness of the setting, the sensitive nature of the noise receptors, the magnitude of the noise increase, the number of residences affected, and the absolute noise level. The significance of noise impacts under CEQA is determined by the Project Development Team (PDT) and is based on the considerations above. For additional information, see Section 7 of the Noise Protocol.

Proposed noise abatement may also have the potential to result in significant adverse environmental effects if the abatement negatively affects other environmental resources, such as designated scenic highways, historic sites, or endangered species.

If the proposed project or the proposed noise abatement would result in a significant environmental effect, then mitigation must be developed and reported in the environmental document. Note that if a soundwall is included as "mitigation" for a potentially significant impact under CEQA, the soundwall must be built, or if the decision is made not to build the soundwall, the environmental document must be revised and potentially recirculated.

Inter-Agency Coordination

There is no "resource" agency for highway traffic noise. It is the responsibility of the Department (under NEPA Assignment) through the approval of environmental documents to ensure compliance with the provisions of 23 CFR 772. For "state-only" projects, the Department is responsible for the environmental document. For further guidance, see SER Volume 1, Chapter 38, "NEPA Assignment."

Property within the state's right-of-way is not subject to local government ordinances. However, all possible effort should be made to comply with the local ordinances.

Links to counties, cities, and local noise ordinances may be found on the following websites:


Noise Study Report(NSR)/Noise Abatement Decision Report (NADR)

The results of a detailed traffic noise analysis are documented in the Noise Study Report (NSR). Section 3 of the Noise Protocol and Section 6 of the Technical Noise Supplement to the Traffic Noise Analysis Protocol (TeNS) describe in detail the process of developing the NSR. The Noise Abatement Decision Report (NADR) is a report that documents the abatement considerations. Both the Noise Study Report and the Noise Abatement Decision Report must be summarized in the draft environmental document.

Preparer Qualifications

Any lead acoustical analyst or staff member responsible for the assessment of traffic noise impacts, traffic noise abatement, or review and approval of final noise reports shall at a minimum have a BS or BA degree in a related field and 5 years of demonstrated experience.

In lieu of 5 years of experience, equivalent qualifications as determined by the Caltrans Division of Environmental Analysis or successful completion of all of the following will be allowed:

Content and Recommended Format

Section 6 of the TeNS describes the proper format of the NSR. A good NSR contains all the necessary information for the reviewer to understand the report with minimum need for further clarification and consultations. A good noise study report contains:

  • Detailed discussion of: land uses, existing and future noise levels, proposed abatement, and the reasonable and feasibility analysis
  • Visual aids: Vicinity maps, project area maps, layouts that clearly indicate the location of affected receptors relative to the project, proposed location of barriers, topographic information, etc.
  • Technical Information: date, time, location, and duration of noise measurements; instrumentation used; inclusion in the appendices of any references mentioned in the report; modeling input and output files; and projected traffic volume data
  • Evaluation of construction noise impacts

The draft NSR must be reviewed, at a minimum, by the District noise specialist (for consultant-prepared documents) and the District Environmental Planner/Generalist responsible for the environmental document. The NSR is approved by the noise specialist’s supervisor (District Branch Chief). For further guidance, see SER Volume 1, Chapter 38, "NEPA Assignment."

Local Assistance Projects - Noise Study Reports prepared in support of local agency Federal-aid transportation projects "off" the SHS have the same review and approval requirements but are processed through the District Local Assistance Engineer (DLAE). The report shall be reviewed by the District noise specialist and the District Local Assistance Environmental Planner/Generalist, and approved by the District noise specialist's supervisor (District Branch Chief).

The NSR is reviewed to ensure that:

  • it complies with the requirements of all applicable federal laws, regulations, policy and guidance
  • the report format and content are consistent with the SER, and
  • the report summary and conclusions are consistent with the information included in the environmental document

Following the Department's internal review of the NSR, the study may be finalized. For further guidance, see "SER Volume 1, Chapter 38, NEPA Assignment."

Information for the Environmental Document

The appropriate environmental document (e.g., Draft Environmental Impact Statement, Environmental Assessment) serves as the vehicle to circulate the preliminary noise abatement (NEPA/23 CFR 772) and CEQA mitigation decisions to the public for review and comment. More information on the process of reporting the preliminary noise abatement and mitigation decision can be found in the Noise Protocol.

Construction Impacts

Construction noise and vibration may only be substantial in exceptional cases, such as when pile driving and crack-and-seat pavement rehabilitation operations will occur. The Noise Protocol, Section 3 and TeNS, Section 6, discusses construction noise. Caltrans Transportation and Construction Vibration Guidance Manual covers the topic of vibration. The FHWA has also developed the Roadway Construction Noise Model (RCNM) for predicting potential construction noise levels.

Timing the Studies with the Environmental Process

The preliminary noise abatement decision (NEPA process) along with the preliminary noise mitigation decision (CEQA process) are incorporated into the environmental documentation. The draft environmental document is publicly circulated and substantive comments are addressed in the final environmental document. An illustration of this process and detailed description of the process are available in the Traffic Noise Protocol (PDF), Figure 2.

Information Needed for Project Delivery

Regional Transportation Plan

This information should be documented in the Environmental Impact Report (EIR) prepared for the Regional Transportation Plan (RTP) and serve as a building block in subsequent decision making.

An RTP requires the preparation of a CEQA environmental document, normally a program or master EIR. Caltrans encourages the Metropolitan Planning Organizations/ Regional Transportation Planning Agencies (MPO/RTPA) to include the following information, as appropriate, in the environmental document for the plan:

  • Project conceptual design (highway on new alignment; substantially change vertical or horizontal alignment of existing highway; or increase number of through lanes; realignment, etc).
  • Land uses (with reference to Noise Abatement Criteria categories).
  • Locations of potentially sensitive receptors within subarea or corridor under study (such as hospitals, schools, churches, libraries, auditoriums, public meeting rooms, motels, hotels, residences, recreational facilities and lands on which serenity and quiet are of extraordinary importance and which serve an important public need).
  • Existence of local noise ordinances covering the corridor or subarea.

Project Initiation Document

Project Study Reports (and equivalents) should contain an inventory of environmental resources, identification of potential environmental issues, and anticipated environmental determination or document type. Potential mitigation requirements and associated costs are also identified. During this project planning phase, it may be more efficient to separate Type I work from other work. If the project covers a large area, and any small portion is determined to have Type I work, the entire project will require a noise study report.

For Local Assistance projects, complete the Preliminary Environmental Study (PES) form. (See Local Assistance Procedures Manual Forms, Chapter 6.)

For projects on the SHS, the following information concerning noise is to be documented in the Preliminary Environmental Analysis Report and included in the PID:

  • Potential noise receivers (receptors) within or adjacent to the project.
  • Potential noise impacts.
  • Possible need for noise abatement measures.
  • Monitoring need.

Draft Project Report and Noise Abatement Decision Report (NADR)

The information contained in the NSR and NADR must be presented in the draft environmental document. Include the proposed configuration of any noise abatement measures considered.

Project Report

In addition to the information provided in the draft environmental document, also provide the following information in the final environmental document:

  • Noise abatement that is likely to be incorporated into the project.
  • Cost estimates for abatement and mitigation measures.

Activities That May Occur During Project Design

Project re-analysis may be necessary if:

  • Undeveloped land becomes permitted for development after the noise analysis but before the project "Date of Public Knowledge" (see the Noise Protocol for a definition of this item).
  • A project re-evaluation may be needed if 1) there has been a significant change in design or scope, or 2) the project is proceeding to the next major federal approval (i.e., authority to undertake final design, authority to acquire a significant portion of the right-of-way, or approval of the plans, specifications, and estimates), or 3) more than three years have elapsed between milestones for an Environmental Impact Statement.

Activities That May Occur During Construction

During the construction the Project Engineer or Resident Engineer may need to take action to resolve issues arising from:

Noise Considerations During Maintenance and Owner-Operator Activities

There are no known maintenance and owner-operator activities that require noise considerations.

(Last content update: 06/29/2021)