Verification of MICNOISE Computer Program for the Prediction of Highway Noise: Part II: Additional Verification of MICNOISE Version 5

About the report:

This is a continuation of an earlier report in which the MICNOISE computer program for the prediction of highway noise was evaluated. The outputs of the MICNOISE program are the L50 and LI0 sound pressure levels, i.e., those levels experienced 50% and 10% of the time. In the earlier report, it was noted that there were difficulties when truck volumes were low. To overcome these, a modified version was proposed, which is now referred to as MICNOISE 2X. In this continuation of the earlier report, a new version of MICN0ISE, Version 5, is evaluated. Also, an experimental variant, 5X, and a variant proposed by the Virginia Department of Highways and Transportation, 5V, are evaluated. In MICN0ISE 5X, the elevation corrections due to trucks are modified as though the truck frequency spectrum were shifted to half the corresponding frequencies for autos. In MICN0ISE 5V, truck noise is assumed to originate 13.5 ft. (4.l m) above the highway, as compared with 8 ft. (2.4 m) for Version 5. It had been found earlier that for 68% confidence 2 dB should be added to the predicted values of MICNOISE 2X. This is shown to increase to 3 dB for MICNOISE, Version 5, but falls again to 2 dB for MICNOISE 5V. However, results for 5V show greater standard deviations, the 68% confidence band being restored only because it is more conservative than MICN0ISE 2X. The reduced accuracy of Version 5 and its variants is attributed to the methods used for handling vertical corrections. It is concluded that MICNOISE 5V is acceptable, but that the earlier methods of elevation correction are preferable.

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