Figure 1. Proposed Bluegrass Motorsports Development
Project.
Finding detailed but apparently unenforceable With the goals established, the challenge that
Commonwealth of Kentucky noise regulations dat- remained for the URS and Bluegrass team was to
ing back to the 1970s, the authors had to first define accurately depict noise from a transportation-related
defensible acoustical objectives that would mutually source that defied usual classifications. In other
satisfy local government, the Project proponents, and words, while the traffic on nearby Interstate-71 could
the nearest noise-sensitive neighbors. As usual in such and was modeled routinely with FHWA’s TNM, how
cases where existing noise law, ordinances, regulations does one depict the silence of an empty racetrack
and standards (LORS) are absent or lacking, the United during one moment, followed immediately by the roar
States Environmental Protection Agency (USEPA) com- of a Ferrari F430 quickly closing the gap on a pack of
monly-known “levels document”
1
was invoked to set hundred-plus mile-per-hour Corvettes on the straight-
an exterior level of 55 dBA, L
dn
at nearby residential away?
receiver locations as a threshold of significance in
assessing potential noise impacts associated with the 2. NOISE PREDICTION METHOD
development of the Project. When the noise study for this Project was underway,
It should be noted that this impact threshold of 55 URS utilized the version 3.5 series of Cadna/A Noise
dBA, L
dn
is substantially more restrictive and stringent Prediction Model to estimate the Project-generated
than what is typically established for most transpor- sound level at nearby noise-sensitive receivers.
tation noise sources. The FHWA has established a Cadna/A is a Windows® based software program that
loudest hour Leq of 67 dBA in their noise abatement predicts and assesses noise levels based on ISO 9613-
criteria for residential land uses near highways, and 2 standards for noise propagation calculations. The
the Federal Aviation Administration (FAA) generally model accepts sound power levels (PWL, in decibels
applies an Ldn of 65 dBA as justification for noise miti- with respect to 1 picowatt) provided by the user,
gation treatments for residential area near airports. equipment manufacturers and other sources. The cal-
But given the Project’s rural surroundings and related culations account for classical sound wave divergence,
concerns, usage of the quieter noise limit seemed plus attenuation factors resulting from air absorption,
prudent and was likely helpful in securing zoning and basic ground effects, and barrier/shielding.
other pre-construction approvals and permits for the
The Official Magazine of the NSBE Alumni Extension November 2009 | Alumni Arsenal • 19
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