Traffic Noise Analysis For Transportation Projects: A Beginner’s Guide – Part I

February 12, 2014

Justin K. Kellogg, M.S., QEP, Environmental Engineer gives us a beginners look into Traffic Noise Analysis for Transportation Projects.

Aside from the deep “thunder” of a finely tuned Lamborghini Diablo motoring by at mach 0.28 or the “growl” of a six-ton monster truck crushing half a dozen small cars in a matter of seconds, most people are not big fans of traffic noise. As a matter of fact, I don’t think I’ve EVER met a person who is fond of it.

Cars, trucks, busses, motorcycles…of course we must use them, but, after we are finished riding in them, parking them, or hopping off of them at the bus stop, we typically don’t want to hear their roar again until we need to. Yet, since this is our major form of transportation to pretty much everywhere, the relentless din of traffic noise will almost always be within earshot. So how much traffic noise is too much?

Traffic noise is so integrated into our lives that we tend to accept a certain amount of background noise, but, when it gets too loud we tend to get annoyed – some of us more than others.

Given that our threshold for traffic noise varies from person-to-person due to factors ranging from personal preference and hearing loss to on-the-job necessity, how can you possibly quantify it? Well, there actually IS a way.  Based on land use and past data collected from noise complaints, the Federal Government developed traffic noise standards, better known as the Code of Federal Regulations 23 CFR 772. These standards have been very successful in reducing traffic noise complaints.

Now this may not sound very important to those of you who live, work or recreate in locations that currently have noise levels below what you would consider to be extreme, but, what if that were to change and impact YOU? I expect the subject would suddenly become extremely important as it could begin to impact your sleep, anxiety level, property value, daily productivity, etc. You get the picture.  Well, that’s precisely when a Traffic Noise Study may be needed.

Proposed projects such as new roadways, modifications to roadways, or new traffic patterns that may affect traffic noise are studied in an effort to avoid traffic noise impacts. Traffic noise is studied in coordination with both the environmental review process and standards set by agencies such as the New York State Department of Conservation and the U.S. Environmental Protection Agency (e.g. SEQR or NEPA) and with the design of transportation projects.  Transportation projects are environmentally “screened” up front in order to identify, among other things, potential noise concerns.

Most transportation projects will not require a detailed noise analysis, for example field noise measurements and computer modeling. Projects that do require a detailed noise analysis, however, are generally those that will change roadway conditions. These may include moving roads closer to houses, removing sound barriers, an increase in the number of heavy vehicles, etc., and those found in 23 CFR 772.5 of the Code of Federal Regulations under a Noise Type I Project. If noise concerns can be identified up-front during the design process, noise mitigation measures can often be incorporated to reduce noise impacts and post-construction noise complaints.

Now let’s say you have a project that is a Noise Type I Project and it will require a detailed noise analysis. What do you do next? Well, as experienced noise consultants, Watts Architecture & Engineering (Watts) can perform a detailed Traffic Noise Study for your transportation project.

There are several steps involved in preparing a detailed noise analysis. These include:

1. Knowledge of the Project Area – Getting to know the project site is critical. Generally, a site visit and some in-depth research must be performed to identify current or proposed land uses along the project corridor that may be affected by an increase in traffic noise. With the exception of parking lots, places such as churches, schools, recreation areas, residences, and other “exterior areas of human use” as we refer to it in the industry, will generally become the focus of a noise analysis.

2. Choosing “Receiver” Sites – After noise-sensitive areas along the project corridor are identified, noise-sensitive “receiver” sites are chosen. These sites are simply representative locations that will undergo field noise measurement and detailed computer analysis. Some projects may turn out to have two or three receiver locations while others may have 50 or more!

3. Measurements & Data Collection - Once we know where the noise meter receivers need to be placed, we then gather a team together (generally three to eight people depending upon site conditions) to measure traffic noise and collect traffic data at each receiver location. During the field noise measurements, detailed traffic data must be collected including speeds and separate counts of passing automobiles, medium trucks, heavy trucks, busses, and motorcycles. This simultaneous traffic data collection must be performed for each roadway that can be heard from each receiver. Needless to say, in urban areas, that can translate into a lot of coordination during a noise measurement session and lots of walkie-talkies! The collected traffic data and field noise measurements are then required for use in the computer noise modeling effort.

4. Developing a Virtual Computer Model – Next, we enter the virtual world. The actual noise analysis is performed using a computer model. A computer noise model is constructed of the project site as a virtual 3D map (XYZ coordinates) of roadways, grades, and structures that may affect noise propagation along the corridor. So, how do you know that your virtual computer noise model will work? Well, at each receiver location, the virtual computer model is programmed with the traffic data counted and obtained during the field noise measurements to verify that the model will produce sound levels that match “real-world” conditions. Essentially, if the results of a virtual noise model reasonably match the results obtained from the field noise measurements, the virtual model is good-to-go.

Once you know that your computer noise model results meet the defined accuracy standards, you can then adjust the model conditions (e.g. traffic volumes, speeds, geometry, etc.) to suit future conditions and predict future noise levels that would be expected under each design alternative. With this information, educated decisions can then be made as to whether or not noise mitigation measures should be or can be worked into the overall design plans for a new project, thus resulting in a more successful project outcome for all involved.

If you would like to discuss more on this topic, please post a comment/question or email me at jkellogg@watts-ae.com.