Recommended Best Practices for the Use of the FHWA Traffic Noise Model (TNM)
Appendix E. Sample QA Plan
The QA Plan in this appendix presents some concepts that organizations may wish to consider when drafting a QA Plan. Note that this sample QA Plan is provided solely as an example and that the language appearing in it is not mandated by the FHWA. For instance, although some state SHAs may wish to do so, the FHWA is not mandating the amount of experience for different levels of staff who may work on a highway noise study. The sample QA Plan is based on one organization's approach to QA.
Sample Quality Assurance Plan
- The objectives of the Quality Assurance (QA) Plan are to improve the quality of noise models and noise analysis reports prepared by this organization. Adherence and commitment to the policies and procedures outlined herein help ensure, to the degree practicable, that:
- Noise models are accurate and developed in a consistent, traceable, and repeatable manner.
- Noise analysis reports meet all applicable regulatory requirements and present the results of the noise study in a clear and concise manner.
- All members of the highway noise team shall understand and commit to the policies and objectives of the QA Plan.
- The QA Plan will be reviewed and updated, as necessary, on a periodic basis, or in conjunction with planned revisions to the SHA Noise Abatement Policy developed under 23 CFR 772.
- Each highway noise study will be overseen and reviewed by a Principal Investigator (PI) or Principal in Charge (PIC) who has specialized experience in highway noise analysis. The PI typically has 20 or more years of experience, has demonstrated exceptional technical ability, and has shown the ability to find creative and appropriate solutions to complex technical problems. The PI often serves as the Project Manager (PM) on the largest or most complex highway noise projects. On smaller or less complex projects, the PM often has 5 or more years of experience in highway noise analysis. In such cases, a PI will always serve in an oversight and review capacity for the PM.
- The PI will review each study proposal for the completeness and reasonableness of the proposed staffing, scope of work, schedule, and cost budget.
- At the beginning of the study, the PI and/or PM will review all mapping and traffic data provided for the noise analysis to ensure that the data are sufficient. For example, mapping must be extensive enough to include all potentially impacted land uses, and traffic data must be sufficient to allow computation of the loudest hour of the day, as required by the FHWA.
- On the larger projects, which require a number of staff members working simultaneously, regular project team meetings shall be held by the PM to ensure accuracy and consistency among all of the team members.
- Before conducting highway noise measurements, all staff members shall be trained in all aspects of measurement by experienced senior staff, or through approved training courses and/or programs.
- During noise measurement surveys for roadway improvement projects, traffic classification counts shall be conducted simultaneously with noise measurements of the existing facility whenever possible. These traffic counts will then be used as input to the noise prediction model to compute noise levels from the existing facility at the measurement locations. Comparison of the measured noise levels to the computed levels will serve to validate the noise model or to assist in refining modeling assumptions that relate to sound propagation.
- Before performing any noise modeling, all staff members shall be trained in all aspects of highway noise prediction and the details of the models by qualified senior staff, or through approved training courses.
- Upon completion of a TNM model for a highway project, the PM shall review the modeled geometry and traffic input with the analyst, and as needed, complete a TNM Object input checklist to document the review.
- For NEPA noise studies, the PI and/or PM shall review the predicted noise levels at each reported measurement and prediction location for each of the project alternatives to ensure consistency of predicted noise levels among multiple alternatives. Differences in predicted levels among alternatives shall be evaluated to determine the appropriateness of the observed differences. Where differences are greater or less than expected by the PI and/or PM, or where sound levels appear incorrect, the input data, calculation procedures, and modeling assumptions shall be reviewed and discussed. TNM-computed noise levels shall not be finalized until all reported noise levels are reviewed and approved by the PI and/or PM.
- Prior to finalizing the noise impact inventory, the PI and/or PM shall carefully review the inventory numbers by FHWA Activity Category and by alternative and the locations of the impacted properties. The review evaluates both the appropriateness of impact numbers along each alternative and the differences among alternatives. Where, in the judgment of the PI/PM, inventory numbers or impact locations appear to be inappropriate or inconsistent among alternatives, the approach, analysis, and assumptions shall be reviewed, and the impact inventory shall not be finalized until all reported numbers meet the approval of the PI/PM.
- The noise abatement (acoustical) design shall be conducted in accordance with the individual SHA's requirements pertaining to barrier feasibility and reasonableness. Prior to finalizing any noise abatement design, the PI and/or PM shall carefully review the details of each barrier concept including location, height, length, range of insertion loss predicted, number of homes protected, cost, and cost effectiveness. Based on professional judgment, the PI and/or PM may provide suggestions to modify the design to improve cost-effectiveness, provide additional protection, or limit cost. In the case of final barrier design studies, after barrier designs are finalized to the satisfaction of the PI/PM, they shall be submitted to the SHA for review prior to submitting a draft noise study report. Finally, modifications to the abatement designs shall be made as requested by the SHA, prior to submitting the final noise study report.
- All draft and final versions of noise study reports and noise abatement design reports shall be reviewed and approved by the PI and/or PM before submittal to the SHA.
- All checklists prepared for TNM object input and/or noise analysis reports should be submitted to the SHA as part of the project closeout process.
