Traffic Projections in Noise Analysis

Traffic volumes are an integral part of any highway traffic noise analysis. The defining procedure for federal regulation for highway transportation noise analysis is 23 CFR 772. Section 23 CFR 772.9 Traffic Noise Prediction (d) states "In predicting noise levels and assessing noise impacts, traffic characteristics that would yield the worst traffic noise impact for the design year shall be used." States have the discretion to determine how to interpret what traffic metrics they use in their federally approved noise analyses. For example, some states use Level of Service (LOS) traffic volumes, while others use peak hour or design hour volume. Some states use an in-depth method to determine loudest hour which incorporates traffic volumes for a twenty four hour period and their corresponding operating speed per hour. This paper will discuss the time and effort associated with each procedure. Case studies will be presented to determine which of these traffic metrics best matches the current traffic counts.