FHWA Traffic Noise Model

Background

Prior to the release of the FHWA TNM, the FHWA Highway Traffic Noise Prediction Model (FHWA-RD-77-108), or "108 model," was in use for over 20 years. Although an effective model for its time, the "108 model" was comprised of acoustic algorithms, computer architecture, and source code that dated to the 1970s. Since that time, significant advancements have been made in the methodology and technology for noise prediction, barrier analysis and design, and computer software design and coding. Given the fact that over $500 million were spent on barrier design and construction between 1970 and 1990, the FHWA identified the need to design, develop, test, and document a state-of-the-art highway traffic noise prediction model that utilized these advancements. This need for a new traffic noise prediction model resulted in the FHWA TNM.

The core vehicle noise emissions database for the "108 model" was collected in the mid 1970s. Because of the age and associated limitations with this database (e.g., no data for vehicles on grade or vehicles subject to interrupted-flow conditions), it was essential that a state-of-the-art, nationally representative database be developed for the FHWA TNM. A state-sponsored, pooled-fund effort supported the development of the national reference energy mean emission levels (REMEL) database for the FHWA TNM. Between 1993 and 1995, data were collected for over 6000 vehicle pass-bys at over 40 sites in 9 states across the country.

In March 1998, the Federal Highway Administration (FHWA) released the Traffic Noise Model, Version 1.0 (FHWA TNM®). It was developed as a means for aiding compliance with policies and procedures under FHWA regulations. Since its release in March 1998, Version 1.0a was released in March 1999, Version 1.0b in August 1999, Version 1.1 in September 2000, Version 2.0 in June 2002, Version 2.1 in March 2003 and the current version, Version 2.5 in April 2004. The FHWA TNM is an entirely new, state-of-the-art computer program used for predicting noise impacts in the vicinity of highways. It uses advances in personal computer hardware and software to improve upon the accuracy and ease of modeling highway noise, including the design of effective, cost-efficient highway noise barriers.

The FHWA TNM® is a registered copyright and trademark.

The FHWA TNM contains the following components:

• Modeling of five standard vehicle types, including automobiles, medium trucks, heavy trucks, buses, and motorcycles, as well as user-defined vehicles.
• Modeling of both constant-flow and interrupted-flow traffic using a 1994/1995 field-measured data base.
• Modeling of the effects of different pavement types, as well as the effects of graded roadways.
• Sound level computations based on a one-third octave-band data base and algorithms.
• Graphically-interactive noise barrier design and optimization.
• Attenuation over/through rows of buildings and dense vegetation.
• Multiple diffraction analysis.
• Parallel barrier analysis.
• Contour analysis, including sound level contours, barrier insertion loss contours, and sound-level difference contours.

These components are supported by a scientifically founded and experimentally calibrated acoustic computation methodology, as well as an entirely new, and more flexible data base, as compared with that of its predecessor, Stamina 2.0/Optima. The database is made up of over 6000 individual pass-by events measured at forty sites across the country. It is the primary building block around which the acoustic algorithms are structured. The most visible difference between the FHWA TNM and Stamina 2.0/Optima, is the FHWA TNM's Microsoft Windows interface. Data input is menu-driven using a digitizer, mouse, and/or keyboard. Users also have the ability to import Stamina 2.0/Optima files, as well as roadway design files saved in CAD, DXF format. Color graphics will play a central role in both case construction and visual analysis of results.

Prior to the release of the FHWA TNM, the FHWA Highway Traffic Noise Prediction Model (FHWA-RD-77-108), or "108 model," was in use for over 20 years. Although an effective model for its time, the "108 model" was comprised of acoustic algorithms, computer architecture, and source code that dated to the 1970s. Since that time, significant advancements have been made in the methodology and technology for noise prediction, barrier analysis and design, and computer software design and coding. Given the fact that over $500 million were spent on barrier design and construction between 1970 and 1990, the FHWA identified the need to design, develop, test, and document a state-of-the-art highway traffic noise prediction model that utilized these advancements. This need for a new traffic noise prediction model resulted in the FHWA TNM.

The core vehicle noise emissions database for the "108 model" was collected in the mid 1970s. Because of the age and associated limitations with this database (e.g., no data for vehicles on grade or vehicles subject to interrupted-flow conditions), it was essential that a state-of-the-art, nationally representative database be developed for the FHWA TNM. A state-sponsored, pooled-fund effort supported the development of the national reference energy mean emission levels (REMEL) database for the FHWA TNM. Between 1993 and 1995, data were collected for over 6000 vehicle pass-bys at over 40 sites in 9 states across the country.

The FHWA TNM (Version 1.0) was released in March of 1998. The model was the culmination of six years of extensive research. It included a new/expanded vehicle noise emissions database and state-of-the-art acoustical algorithms. After the release, a survey was distributed to FHWA TNM users to allow user input for program Graphical User Interface (GUI) enhancements and bug fixes. This list was prioritized, and many of the enhancements/bug fixes were incorporated into FHWA TNM Versions 1.0a, 1.0b, and 1.1. Version 1.1 also included a major improvement to the computational speed of the program, upgrading the architecture from 16 to 32-bit. Unfortunately, this version also introduced some new bugs. Version 2.0, released in June 2002, focused on removing Version 1.1 bugs, while maintaining the faster computational speed. Version 2.1, released in March 2003, fixed additional bugs and included over 20 enhancements to the TNM GUI. Version 2.5, released in April 2004, is the first version of the software, since the original release, with major improvements to the acoustics.

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