Environmental Noise
We live in an increasingly noisy world. As population densities increase, there is less available buffer space between noise sources and homes. Homes are increasingly built closer to highways and industrial land uses. Often, noisy activities are forced into close proximity with noise-sensitive areas such as residences, hospitals or parks.
Noise can degrade the quality of life, interfere with sleep, and can adversely affect property values.
Having worked on hundreds of environmental noise projects since 1984, we have considerable experience studying outdoor noise problems, and developing mitigation measures. We use standard modeling techniques to predict traffic noise, aircraft noise contours, and railroad noise. Once noise levels are known (either by measurement or prediction) appropriate actions can be taken to minimize the effects on surrounding areas. We often act as technical experts at public hearings regarding the assessment of noise impacts.
Traffic noise is determined by the daily and peak-hour volume of traffic, travel speed, number of lanes, terrain, type of vehicles and the location of the affected receivers, usually residences. The most practical mitigation is typically a roadside noise barrier. Sound-rated windows and exterior walls can also be used to reduce noise levels indoors. The FHWA Traffic Noise Model (TNM) is used to analyze and predict traffic noise based on the parameters mentioned above. TNM is also used design adequate noise barriers.
Aircraft are loudest on take-off, especially for locations behind and under the departure flight path. Landing aircraft are typically much quieter. The FAA has published the Integrated Noise Model (INM) and Helicopter Noise Model (HNM). These computer models are used to generate noise contours or "footprints" of average noise levels based on the number of operations and aircraft types. Areas exposed to levels above Ldn 65 are considered to be "noise impacted".
Railroad operations can also create significant noise levels. DOT regulations require that a horn or signal of a certain sound level be used at road crossings. Diesel locomotives produce a great deal of low frequency noise. Once the locomotive is past, squealing wheels, air brakes and other track noises remain. Standard FTA methodology is used to predict railway noise, based on number of trains, track conditions, speed, grade, and similar factors.
Recreational vehicles and activities can create unpleasant noise levels in some of the quietest areas. Snowmobiles, motorcycles and ATV's travel into quiet parks and wooded areas, disturbing the peace and quiet that make such areas appealing in the first place. Personal water craft (jet-skis) can be a real nuisance to lakefront homes.
HUD and other federal agencies specify the acceptable noise levels for
residential projects. For sites exposed
to noise above Ldn 60, there is the potential for impact. Sites exposed to outdoor noise up to Ldn 65 are
considered “normally acceptable” for residential development. HUD requires a noise study whenever the site
is within certain distances of major roads, rail lines or airports. The study needs to look at both present and
future conditions. Future conditions
need to be projected at least ten years out, but twenty years is the standard
of practice.
MULLINS ACOUSTICS has the capability to measure and model many noise
environments. We own sound level meters that can measure frequency
content, and other sound meters that can log data continuously for days at a
time, collecting statistical data on minimum, maximum and average sound
levels. The typical project will need a
24-hour noise measurement, with data taken hour by hour. That captures the normal variation of noise
during the day and night as activity patterns change.