Highway traffic creates noise—and sometimes the negative impacts of noise in an area need to be mitigated or minimized. To do so, a project team must first conduct a highway traffic noise analysis to determine whether noise impacts exist and to consider and design potential mitigation measures—noise abatement—to reduce those impacts. Designing noise abatement requires understanding basic acoustic principles, regulatory requirements, public expectations, and some engineering considerations.

To assist with regulatory compliance related to noise impact determinations and noise abatement design, the Federal Highway Administration created the Traffic Noise Model (TNM) software. The TNM line of software packages has been around for over two decades. FHWA released TNM 3.0 in February 2020 and will soon release the next version, TNM 3.1.

FHWA worked closely with the Volpe National Transportation Systems Center to complete the version 3.1 update. The development focused on fixing software bugs and addressing feedback and feature requests from active TNM 3.0 users.

Increased Functionality

TNM 3.1 now includes an installer, parallel processing of receivers, and removal of the database saving structure. The updates should decrease the memory usage and runtimes of the software.

TNM 3.1 corrects some minor acoustical calculation issues from TNM 3.0, although there have been no changes to the underlying acoustical assumptions or metrics since the last release. The developers updated the data model for TNM 3.1 with improved error checking and error handling compared to TNM 3.0, so that version 3.1 can provide results for project models that would have errored out in TNM 3.0.

This screenshot of the TNM 3.1 Graphical User Interface displays the various areas and windows available for the user to input and review data. The main window is a streetview map of the example project area.

TNM 3.1 also offers an improved user interface and data connections. These changes were made in response to detailed user feedback regarding important functionality and data visibility required to conduct a highway traffic noise analysis on a typical project. For example, the Barrier Design Table now shows sound source contributions by barrier segment and offers the ability to filter and sort the data in the table. TNM 3.1 also enables the user to import existing TNM model files that include coordinate systems, projections, and adjustments. For more information regarding the updates, please see the Release Notes and TNM 3.1 Fact Sheet at www.fhwa.dot.gov/environment/noise/traffic_noise_model/tnm_v31/index.cfm. To further expand TNM's functionality, FHWA is developing a Noise Screening Tool that allows simplified inputs and outputs to enable users to determine the likelihood of noise impacts occurring before engaging in a full-scale noise analysis.

Ongoing Maintenance and Future Enhancements

FHWA has set a target schedule to provide annual or semi-annual releases of TNM. This will enable the development team to respond quickly to user requests, enhancement ideas, and new software programing protocols. The TNM 3.0 acoustics and TNM 3.1 functionality will be used to update the Roadway Construction Noise Model (RCNM). In addition, the team is evaluating whether it is possible to integrate TNM and RCNM into a single highway noise model.

FHWA continues to engage the user community through training, regular email updates, and meetings. For further information on using TNM, visit the instructional demonstration videos on the TNM playlist at www.youtube.com/playlist?list=PL5_sm9g9d4T3naH9knm5E6SZUpmI_QD3y. The FHWA Resource Center also offers training via a multi-day course. The lessons are currently instructor-led, but virtual.

For more information, contact Aileen Varela-Margolles at a.varela-margolles@dot.gov.

Aileen Varela-Margolles is an environmental specialist on the Air Quality and Noise Team in FHWA's Office of Environment, Planning, and Realty.