Some of you recently met our noise analysts that have been working in your community. Noise complaints are frequently associated with transportation activities (highway, airplanes, and trains), and this analysis is a regular component of PENNDOT planning studies.
By definition, noise is "unwanted sound." But that could create a lot of confusion since what is music to one person can be noise to another. So PENNDOT and the Federal Highway Administration (FHWA) have developed measurable standards to define noise. For residential areas (and related land uses like schools and parks), a highway project would create a noise impact if the predicted level is expected to approach or exceed 67 dBA. In addition, a project would create an impact if the future noise levels are expected to be 10 dBA higher than the existing levels, which PENNDOT considers to be a substantial increase. So what is a "dBA"? Noise is measured in units called decibels (dB). But the human ear doesn't hear all sounds equally. We don't hear low pitches as well as higher ones, so a weighting system has been developed to correspond to our response.

We call this "A-weighting," and levels measured with this system are expressed as dBA. Loudness can vary based on how close you are to the source. And similar sources (e.g., trucks) can vary from one to another. That being said, it might be useful to think about common sources, as shown in the table. Another way to think about the noise impact criterion of 67 dBA is to recognize that this is the normal range for conversation. In fact, that impact standard was set based on concerns for interference with communication, such as talking across the picnic table in your back yard. For the other impact standard, a 10-dBA increase would generally be perceived as a doubling of the noise level.
When noise impacts are predicted, the study team must look at the viability of noise abatement. That might mean a noise wall or roadside berm would be included if a new highway is constructed. But these mitigation features are only included if they are shown to be feasible and reasonable. In addition to the noise measurements that were made in August, the analysis uses a computer model developed by FHWA, which permits prediction

of noise conditions in the future and an assessment onthe effectiveness of mitigation measures. These analyses will be used in the preparation of the Environmental Impact Statement.
For more information on noise you can visit with our noise consultant at the next public meeting. Or you can use the Internet to get background on the policies and procedures from the PENNDOT Traffic Noise Handbook
ftp://ftp.dot.state.pa.us/public/pdf
pennDOTpub24.pdf) or visit the FHWA web site (http://www.fhwa.dot.gov/
environment/noise/index.htm). Please note that you will need the free Adobe Acrobat Reader (http://www.adobe.com) to view the PENNDOT Manual.