Living with noise: planning land use with highway traffic noise in mind can help local agencies improve residents' quality of life

Public Roads, July-August, 2003 by Chris Corbisier

According to the most recent data available from 1987, noise from highway traffic affects more than 18 million people in the United States. As highway systems continue expanding, increased traffic volumes result in higher levels of traffic noise for residents of adjacent neighborhoods. New residential development typically occurs near roadways because of the case of traveling to work, school, and leisure and shopping activities. But as open space for new development becomes scarce, must people simply accept increases in highway traffic noise? Not necessarily.

Avoiding a noise problem frequently is more effective than trying to correct an existing one using noise barriers. FHWA encourages developers, government officials, planners, and private citizens to consider ways to address highway traffic noise before--rather than after--frustrating problems arise. One solution is noise-compatible land-use planning.

Through advance planning and shared responsibility, local governments and developers, working cooperatively with Federal and State governments, can plan, design, and construct new development projects and roadways that minimize the adverse effects of noise from highway traffic. Noise-compatible land-use planning encourages the location of less noise-sensitive land uses near highways, promotes the use of open space separating roads from developments, and suggests special construction techniques that minimize the impact of noise from highway traffic.

Sound Basics

Acousticians define sound as a sensation in the ear created by pressure variations or vibrations in the air. What qualifies as noise, or unwanted sound, tends to be subjective. That is, sound that one person perceives as music may be noise to someone else.

Sound is composed of many frequencies, some of which may affect one person more than another. Because engineers measure sound in decibels (dB) on a logarithmic scale, when two sources of sound, each measuring 70 dB(A), are added together, the resulting sound level is not 140 dB(A) but 73 dB(A). The (A) refers to a weighting scale that approximates the manner in which humans hear higher frequencies better than lower frequencies.

Levels of highway traffic noise typically range from 70 to 80 dB(A) at a distance of 15 meters (50 feet) from the highway. These levels affect a majority of people, interrupting concentration, increasing heart rates, or limiting the ability to carry on a conversation. The noise generated by a conversation between two people standing 1 meter (3 feet) apart is usually in the range of 60-65 dB(A). Most people prefer the noise levels in their homes to be in the 40-45 dB(A) range, similar to the levels found in a small office. A reduction of sound from 65 to 55 dB(A) reduces the loudness of the sound by one half, while a reduction of sound from 65 to 45 dB(A) results in a loudness reduction of one quarter.

Common Outdoor and Indoor Noises

                               Sound   Sound
                           Pressures   Pressure
                               (uPa)   Levels
   Outdoor Noises                      (dB)      Indoor Noises

                           6,324,555   110    Rock Band at 5 m
Jet Flyover at 300 m
                           2,000,000   100    Inside Subway Train
Gas Lawn Mower at 1 m                           (New York)
                             632,456   90     Food Blender at 1 m
Diesel Truck at 15                            Garbage Disposal at 1 m
Noisy Urban Daytime          200,000   80     Shouting at 1 m
Gas Lawn Mower at 30 m        63,246   70     Vacuum Cleaner at 3 m
                                              Normal Speech at 1 m
Commercial Area               20,000   60
                                              Large Business Office
Quiet Urban Daytime            6,325   50     Dishwasher Next Room
Quiet Urban Nighttime          2,000   40     Small Theatre, Large
                                              Conference Room
                                                (Background)
Quiet Suburban Nighttime                      Library
                                 632   30
                                              Bedroom at Night
Quiet Rural Nighttime                         Concert Hall (Background)
                                 200   20
                                              Broadcast and Recording
                                                Studio
                                  63   10
                                              Threshold of Hearing
                                  20   0

Source: FHWA

Reducing Noise from Highway Traffic

FHWA recognizes three broad approaches for reducing noise from highway traffic: source control, mitigation measures associated with the design of road projects or their operation, and noise-compatible land-use planning.

Source control in the United States involves regulating and enforcing the level of noise emissions from newly manufactured medium and heavy trucks with a gross vehicle weight rating of more than 4,525 kilograms (10,000 pounds). The level of noise emitted by trucks has decreased by 3 dB(A) in the past 20 years. Noise from automobiles, however, is not regulated.