Noise Modeling and Measurement Content

Noise Modeling and Measurement Content

FHWA Traffic Noise Model

The FHWA TNM 2.5 Noise Model is the current model version. To comply with 23 CFR, Part 772.17 the FHWA TNM 2.5 is required to be used on all Federal-aid highway projects. 

ADOT EP Noise team is suggesting a default approach for modeling inputs, based on the environmental conditions and level of noise analysis, provided in Instruction on using FHWA TNM in noise analysis. The instructions promote streamlining (FHWA-HEP-17-061), consistency and facilitating comparisons of modeling results between projects and alternatives. It is a dynamic document and may change following the development of new noise modeling tools as approved by FHWA, such as TNM 3.0. These recommendations rely on FHWA’s reports FHWA-HEP-16-018 - Recommended Best Practices for the Use of the FHWA Traffic Noise Model (TNM) and NCHRP Report 791 - Supplemental Guidance on the Application of FHWA’s Traffic Noise Model (TNM). Please visit webinar for the demonstration of the best practices (requires installation of Adobe Connect Add-In).

ADOT strongly encourages consultants to familiarize themselves with FHWA TNM 3.0. Webinars were held in March 2017 and provide basic information on standalone version of TNM 3.0, and Add-ins for ArcGIS, AutoCAD, and Microstation.

TNM 2.5 to TNM 3.0 Conversion tool

Traffic Noise Measurements

Current FHWA guidelines on determining existing-noise in the vicinity of a highway or determining vehicle noise emissions for use with highway noise prediction models; highway barrier insertion loss; noise reduction due to buildings in the vicinity of a highway, and Highway-related occupational noise exposure are provided in FHWA Measurement of Highway-Related Noise - Report.

ADOT EP Noise team have provided an Instruction on Determination on Existing Noise levels and Noise Measurement Data Form.

Field measurements are required, as existing background noise is usually a composite from many sources, and noise prediction models are applicable only to noise originating from a specific source. If it is clear that existing noise levels at locations of interest are predominantly due to a highway, then the existing noise levels may be calculated using the validated FHWA highway traffic noise prediction model.

For the purpose of validation of the FHWA TNM, the noise level measurements taken must be representative of free-flow conditions, without traffic controls, away from sound reflective objects (warehouses, parked trucks, privacy walls etc.), without being influenced by other noise sources (aircrafts, lawn mowers, engines running, running water, loud insects, birds, animals), and with a clear view to the roadway. When and where possible, it is recommended to take two noise measurements simultaneously, with sound level meters placed on the same line perpendicular to the highway, the farther being approximately within 400 ft from the highway, while the other placed half the distance.