Verification of MICNOISE Computer Program for the Prediction of Highway Noise

About the report:

The objectives of this study were to verify the computer program used by the Virginia Department of Highways to predict highway sound pressure levels, to determine whether the accuracy and usefulness of the program could be improved, and to make recommendations for future research. In the report, the recommendations of NCHRP Report 117 are described briefly because they are the core of the computer program used by the Department. Next, MICNOISE, the Virginia Department of Highways' version of the Michigan/117 computer program, is discussed. Instrumentation, measurement methodology, and analytical techniques are described in detail. On the basis of the evaluation of the predicted sound pressure levels (SPL) against the measured SPL the following conclusions are presented: The revised MICNOISE 5 computer program predicts L10 levels within + 2 dB of actual values, to 68% confidence limits; Further changes in the MICNOISE program will not materially improve the results; Various inherent limitations in the MICNOISE model dealing with final dB summing, the assumption of uniform vehicle separation, the use of the inverse 1 1/2 power law, the absence of a specification for confidence levels, and the lack of an accounting for separate sources of noise in the prediction of noise made by a vehicle are enumerated. It is recommended that: The revised MICNOISE computer program be used essentially as is for the prediction of L10 levels within the aforementioned confidence limits; Further changes to MICNOISE that would alter the predicted levels are not warranted; An evaluation of the predictions for highway barriers should be made; A new prediction program that would avoid the present limitations on MICNOISE should be developed.

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