Federal Highway Administration's Traffic Noise Model (FHWA TNM®), Version 1.0 - Technical Manual

Final Report February 1998

FHWA-PD-96-010

DOT-VNTSC-FHWA-98-2

Prepared for
U.S. Department of Transportation
Federal Highway Administration
Office of Environment and Planning
Washington, DC 20590

Prepared by
U.S. Department of Transportation
Research and Special Programs Administration
John A. Volpe National Transportation Systems Center
Acoustics Facility
Cambridge, MA 02142-1093

Notice

This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or use thereof. This report does not constitute a standard, specification, or regulation.

The United States Government does not endorse products or manufacturers. Trade or manufacturers' names appear herein solely because they are considered essential to the object of this document.

Preface

This Technical Manual is for the Federal Highway Administration's Traffic Noise Model (FHWA TNM®), Version 1.0 -- the Federal Highway Administration's computer program for highway traffic noise prediction and analysis. A companion User's Guide describes how to use TNM [Anderson 1998]. In addition, a companion technical report documents the vehicle noise-emissions data base [Fleming 1995].

Overview of TNM: TNM computes highway traffic noise at nearby receivers and aids in the design of highway noise barriers. As sources of noise, it includes 1994-1995 noise emission levels for the following cruise-throttle vehicle types:

• Automobiles: all vehicles with two axles and four tires -- primarily designed to carry nine or fewer people (passenger cars, vans) or cargo (vans, light trucks) -- generally with gross vehicle weight less than 4,500 kg (9,900 lb);
• Medium trucks: all cargo vehicles with two axles and six tires -- generally with gross vehicle weight between 4,500 kg (9,900 lb) and 12,000 kg (26,400 lb);
• Heavy trucks: all cargo vehicles with three or more axles -- generally with gross vehicle weight more than 12,000 kg (26,400 lb);
• Buses: all vehicles designed to carry more than nine passengers; and
• Motorcycles: all vehicles with two or three tires and an open-air driver/passenger compartment.

Noise emission levels consist of A-weighted sound levels, one-third octave-band spectra, and subsource-height strengths for the following pavement types:

• Dense-graded asphaltic concrete (DGAC);
• Portland cement concrete (PCC);
• Open-graded asphaltic concrete (OGAC); and
• A composite pavement type consisting of data for DGAC and PCC combined.

In addition, TNM includes full-throttle noise emission levels for vehicles on upgrades and vehicles accelerating away from the following traffic-control devices:

• Stop signs;
• Toll booths;
• Traffic signals; and
• On-ramp start points.

TNM combines these full-throttle noise emission levels with its internal speed computations to account for the full effect (noise emissions plus speed) of roadway grades and traffic-control devices.

TNM propagates sound energy, in one-third-octave bands, between highway systems and nearby receivers. Sound propagation takes the following factors into account:

• Atmospheric absorption;
• Divergence;
• Intervening ground: its acoustical characteristics and its topography;
• Intervening barriers: walls, berms and their combination;
• Intervening rows of buildings; and
• Intervening areas of heavy vegetation.

TNM computes the effect of intervening ground (defined by its type, or optionally by its flow resistivity) with theory-based acoustics that have been calibrated against field measurements. In addition, TNM allows sound to propagate underneath selected intervening roadways and barriers, rather than being shielded by them.

During calculation, TNM perturbs intervening barriers up and down from their input height, to calculate for multiple heights. Then during acoustical design of selected barriers, combined with selected receivers, TNM displays sound-level results for any combination of height perturbations. It also contains an input-height check, to determine if noise barriers break the lines-of-sight between sources and receivers. In addition, it provides summary cost and benefit information for each barrier design, from user-supplied unit barrier costs and land-use information.

For selected cross sections, TNM also computes the effect of multiple reflections between parallel barriers or retaining walls that flank a roadway. The TNM user can then enter the computed parallel-barrier degradations as adjustment factors for individual receivers in TNM's calculation of receiver sound levels.

TNM computes three measures of highway traffic noise:

• L_Aeq1h :hourly A-weighted equivalent sound level (1HEQ);
• L_dn :day-night average sound level (DNL); and
• L_den :Community Noise Equivalent Level (CNEL), where "den" stands for day/evening/night.

TNM computes these three noise measures at user-defined receiver locations, where it also computes several diagnostics to aid in noise-barrier design. In addition, it computes three types of contours:

• Sound-level contours;
• Noise Reduction, i.e., insertion-loss, contours for noise barriers; and
• Level-difference contours between any two noise-barrier designs.

TNM runs under Microsoft® Windows Version 3.1 (or later). Within Windows, it allows digitized input using a generic Windows digitizer driver, plus the import of DXF files from CAD programs and input files from STAMINA 2.0/OPTIMA. Note: TNM will run under Microsoft® Windows 95 or Windows NT, however, TNM is a 16-bit program and will not take full advantage of the 32-bit architecture associated with Windows 95 or NT.

To aid during input and to document the resulting input and barrier designs, TNM shows the following graphical views:

• Plan views;
• Skew sections;
• Perspective views, including a specialized perspective view for noise-barrier design; and
• Roadway profiles.

TNM Version 1.0 replaces FHWA's prior pair of computer programs, STAMINA 2.0/OPTIMA. In addition, TNM's technical manual replaces FHWA's prior prediction model: FHWA Highway Traffic Noise Prediction Model, FHWA-RD-77-108.³

This manual documents the fundamental equations, the acoustical algorithms, and the interactive logic for all computations within the TNM. The manual is organized as follows:

Section 1. Overview of TNM: This section overviews the basic elements of the TNM's prediction model. It describes the basic concepts of the model, from vehicle noise emissions to predicted sound levels.

Section 2. Model Description:This section describes the TNM's prediction model in more detail, with references to the manual's appendixes for detail on algorithms and mathematics. In particular, this section describes:

• Vehicle noise emissions for the TNM's built-in vehicle types.
• Computation of vehicle speeds, where they are affected by upgrades and traffic-control devices.
• Geometrical complexity in the horizontal plane, plus computation of free-field sound levels from a roadway segment.
• Geometrical complexity in the vertical plane, along any line between roadway and receiver, plus the computation of attenuation due to shielding and ground effects along any such line.
• Computation of degradation of barrier insertion loss due to multiple reflections between barriers that flank the roadway.
• Computation of sound-level contours.

In addition, this manual contains the following detailed appendixes:

Appendix A. Vehicle noise emissions;

Appendix B. Vehicle speeds;

Appendix C. Horizontal geometry and acoustics;

Appendix D. Vertical geometry and acoustics;

Appendix E. Parallel barriers;

Appendix F. Contours;

Appendix G. Model verification;

References

Acknowledgments

FHWA TNM® was developed in part by:

U.S. Department of Transportation
Federal Highway Administration

Robert Armstrong, Steven Ronning, Howard Jongedyk.

U.S. Department of Transportation
John A. Volpe National Transportation Systems Center, Acoustics Facility

Overall management, emission-data design/measurement/analysis, propagation-path development, program testing, User's Guide, Technical Manual, TNM Trainer CD-ROM:

Gregg Fleming, Amanda Rapoza, Cynthia Lee, David Read, Paul Gerbi, Christopher Roof, Antonio Godfrey, Shamir Patel.

Harris Miller Miller & Hanson Inc.

Technical management, emission-analysis design, functional requirements, conceptual program design, acoustical algorithms, design/development/testing of acoustical code and vertical geometry, User's Guide, Technical Manual:

Grant Anderson, Christopher Menge, Christopher Rossano, Christopher Bajdek, Thomas Breen, Douglas Barrett, William Robert.

Foliage Software Systems, Inc.

Program design/specification/development/testing, development of horizontal geometry and interfaces, program documentation:

Ronald Rubbico, George Plourde, Paul Huffman, Christopher Bowe, Nathan Legvold.

Special contributors:

Vanderbilt University: William Bowlby -- emission-data design/measurement/analysis, vehicle speeds.⁴
Bowlby & Associates, Inc.: William Bowlby -- TNM Trainer CD-ROM
Serac Technology Group, Inc.: Theodore Patrick -- TNM Trainer CD-ROM
University of Central Florida: Roger Wayson -- emission-data design/measurement/analysis.
Florida Department of Transportation: Win Lindeman -- Funding and management of subsource-height study.
Florida Atlantic University: Stewart Glegg, Robert Coulson -- subsource height measurements.⁵
Maryland State Highway Administration: Kenneth Polcak -- emission data.
Ohio University: Lloyd Herman -- emission data.
Emission-data state agencies: California, Connecticut, Florida, Kentucky, Maryland, Massachusetts, Michigan, New Jersey, Tennessee.

Design and Review Panel:

Domenick Billera, James Byers, Rudy Hendriks, Harvey Knauer, Win Lindeman, William McColl, Kenneth Polcak.

National Pooled-Fund Contributing States:

Arizona, California, Florida, Georgia, Hawaii, Illinois, Indiana, Iowa, Kentucky, Maryland, Massachusetts, Michigan, Minnesota, New Jersey, New York, North Carolina, Ohio, Oregon, Pennsylvania, Tennessee, Texas, Utah, Virginia, Washington and Wisconsin.

The development work of Harris Miller Miller & Hanson, Foliage Software Systems, Vanderbilt University and the University of Central Florida was conducted in part under contract to Foster-Miller, Inc. Vanderbilt University and the University of Central Florida were also under contract to the Volpe Center.

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