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1 Background Over the past decade, consideration of quieter pavement as an alternative to barriers for highway noise mitigation has been advanced by highway agencies and the public. As an abatement measure, barriers have a higher initial cost than quieter pavements but have lower ongoing costs due to minimal maintenance requirements. Additionally, the noise reduction benefit provided by barriers does not change over time. In contrast, the noise reduction provid- ed by quieter pavements typically diminishes with time. Although the initial cost of quieter pavement can be lower than barriers, the ongoing cost needed to maintain the desired noise reduction performance can be greater. Title 23, Part 772, of the Code of Federal Regulations (23 CFR 772) requires that noise analysis be performed for specific types of projects when potentially impacted receptors are present. Although this regulation identifies several noise mitigation measures, it does not include pavements as a noise abatement measure. Developing a rational methodology for evaluating the acoustic and economic features of pavement strategies and barriers will help demonstrate the potential of quiet pavement technology as a noise abatement measure. Overview of the Project This research focused on developing a methodology to account for the acoustic perfor- mance and life-cycle costs of both types of mitigation measurements when used separately or in combination to allow a systematic and fair comparison of abatement alternatives. This methodology provides a means of evaluating pavement strategies and barriers together for feasibility, reasonableness, effectiveness, acoustic longevity, and economic features. It incor- porates the use of (1) on-board sound intensity (OBSI) data to account for the effect of pavement performance on tire noise source levels; (2) the Federal Highway Administration Traffic Noise Model (FHWA TNM®) with a modification to adjust for tireâpavement noise based on OBSI data; and (3) life-cycle cost analysis (LCCA) to compare the costs of barriers, quieter pavement, and combinations of pavements and barriers. The LCCA provided a means for evaluating the economic features of barriers and pave- ment strategies. The modified version of the FHWA TNM allowed for the modification of the ground-level vehicle noise source strength to account for differences in tireâpavement noise levels using OBSI levels. In this manner, TNM can be used to predict the traffic noise levels for different barrier designs, different pavements, and any combinations of these. OBSI can also be used to establish rates at which pavement noise performance degrades over time for purposes of predicting future levels and/or for monitoring the performance of pavement over its life cycle. S U M M A R Y Evaluating Pavement Strategies and Barriers for Noise Mitigation
2In addition to accounting for economic features and acoustic longevity, the methodology provides a means for evaluating feasibility and reasonableness on the basis of overall noise reduction attributable to insertion of the barrier, use of the pavement, or a combination of the two instead of insertion loss only as is done currently. In addition to feasibility and reasonableness, a third evaluation parameter, effectiveness, has been included to go beyond the relative measures of insertion loss and noise reduction to consider the absolute level performance of the noise abatement. This parameter is needed because the relative metrics of barrier insertion loss and tireâpavement noise reduction when considered separately do not necessarily identify the quietest noise abatement alternative. For example, the most effective low traffic noise levels may not be achieved by combining good barrier insertion loss with noisier pavement or by combining a short (or no) barrier with a moderately quieter pavement. The proposed methodology was applied to several typical highway project case studies. These cases demonstrated that the methodology is appropriate for evaluating pavement strat- egies and barriers in order to identify alternatives that meet cost- and acoustic-effectiveness criteria similar to that used currently by highway agencies.
