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The Federal Highway Administration is celebrating 25 years of the Traffic Noise Model (TNM) with the release of an anniversary web page (https://www.fhwa.dot.gov/environment/noise/traffic_noise_model/tnm_25th_anniv/index.cfm). TNM assists policymakers, planners, engineers, and traffic noise analysts in fulfilling the requirements of the highway traffic and construction noise rules in 23 Code of Federal Regulations, Part 772 (https://www.ecfr.gov/current/title-23/chapter-I/subchapter-H/part-772). To best assist stakeholders and users, TNM was developed cooperatively with States, academia, and consultants with a focus on providing the necessary acoustic outputs to make decisions and provide the necessary public information as required by the rule. TNM calculates noise levels from a highway project so analysts can identify potential noise impacts to areas near highways. TNM also calculates the reduction in traffic noise to those areas from noise abatement measures, like noise walls or berms.
The noise rule provides the process and requires using TNM for conducting a noise analysis on applicable Federal aid-funded or FHWA-approved projects. Typically, a validated project-level TNM setup is used first to predict the existing and anticipated noise levels on the roadway. The noise analyst then reviews TNM outputs to determine whether there are impacts. If there are impacts, TNM is used to evaluate noise abatement options and to determine whether they meet the criteria for feasibility and reasonableness from the noise rule, as implemented in the State’s policy.
To meet the criteria, the noise abatement options must be constructable, provide the necessary acoustic reductions, and remain below the maximum cost. If the abatement measure meets these criteria, it is deemed feasible and reasonable and proposed for inclusion in the project. Engineering review is important to the determination of constructability, and further public involvement is necessary to determine if there is public support for the abatement measure. TNM is central to the analysis process because it assists with the determination of whether the abatement measure provides the requisite noise reductions and meets the cost criteria.
“TNM is a state-of-the-art computerized model used to predict noise impacts of highways. The evolving functionality of TNM allows for ease-of-use highway traffic noise modeling, leading to the design of efficient, cost-effective highway noise barriers,” says FHWA Associate Administrator for the Office of Planning, Environment, and Realty (HEP) Emily Biondi.
Before TNM, noise analysts used numerical methods and charts to hand calculate noise impacts on highway projects. From there, the noise modeling technology was used with punch card computers. Finally, in 1978, a program for noise impacts was developed for personal computers. This program was the Standard Method In Noise Analysis (STAMINA) and its associated barrier optimization system called OPTIMA. STAMINA was used for two decades, but as research and technology advanced, FHWA and its partners saw the need to design a new noise model.
FHWA worked with the John A. Volpe National Transportation Systems Center (Volpe), researchers in academia, and the private sector to develop TNM 1.0, which was released in 1998. TNM used a new acoustic database containing reference energy mean emissions levels (REMELs) for different vehicle types and operating conditions. This new REMEL database was developed in cooperation with multiple State departments of transportation (DOTs), based on thousands of field measurements and validated by acoustic experts. TNM has been updated over the past 25 years to add new capabilities and functions, incorporate the latest acoustic science, address different bugs, and improve usability. Each update has relied on the feedback and cooperation of the user community.
TNM 2.5, the version currently required by FHWA’s noise rule, included an updated REMELs database, and relied on State DOT participation and assistance. The next version, TNM 3.0, also started with the prioritization of State DOT needs and cooperative funding agreements. TNM 3.0 updated the acoustics and separated the graphical user interface (GUI) from the acoustics database. This separation of the GUI from the database was an improvement that has allowed for increased responsiveness to user needs and more frequent software releases. The latest version, TNM 3.2, integrates the Roadway Construction Noise Model (RCNM). The combined program of TNM and RCNM now enables the prediction of construction noise levels via the application of the empirical data collected under the National Cooperative Highway Research Program (NCHRP 25-49)(https://onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP25-49/nchrp_25-49RCNM2.0finalreport.pdf).
In response to user feedback and national trends, FHWA developed three new tools associated with TNM: the Traffic Noise Screening Tool (TNST), the TNMAide spreadsheet tool, and the Automated Consistency Test Suite (ACTS). The TNST improves and replaces the Low Volume Road Tool and helps analysts determine whether a more detailed study is needed. The TNMAide spreadsheet tool works with the Database for Air Quality and Noise Analysis, known as DANA, to identify the worst noise hour for a given segment of roadway. ACTS speeds up consistency tests by automating the comparison of other noise models to TNM.
FHWA has responded to TNM stakeholders by including novel elements in each TNM version, such as the user interface, bug fixes, and in acoustic updates. FHWA responds to stakeholders by providing funding opportunities or participating in national research though the NCHRP program, via pooled funds, or by collecting input on beta tests, and group meetings. The future of TNM will continue to involve cooperative research and development. FHWA and Volpe are currently participating in NCHRP 25-66 to update the acoustic database in TNM in response to changing vehicle fleet characteristics. FHWA invites users to continue to share feedback and needs as we look toward the future together.
Aileen Varela-Margolles is the lead noise specialist for FHWA’s Office of Natural Environment (HEPN). She has a decade of experience in highway traffic noise policy and requirements, and a master’s in environmental studies from Florida International University.
Anthony Norman, PE, is an environmental protection specialist with HEPN. He has 12 years of experience in civil and environmental engineering, and earned a bachelor’s in civil engineering from the Ohio State University and a master’s in civil engineering from the University of Kentucky.
Kelly Joy, an environmental protection specialist, is a Pathways intern with HEPN, and holds a bachelor’s in education and public policy from Pennsylvania State University and a master’s in public policy from the University of Massachusetts.
Lilah Morrissey is the marketing specialist for FHWA’s HEP. She has 14 years of professional experience in project management and marketing, and holds a bachelor’s in economics from the University of Central Florida and has a master’s in community and regional planning from the University of Oregon.
For more information about TNM, visit https://www.fhwa.dot.gov/environment/noise/traffic_noise_model/ or contact TNMHelp@dot.gov.
The different versions of TNM are archived online at: https://www.fhwa.dot.gov/environment/noise/traffic_noise_model/old_versions/.
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