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A road surface complying with the new International Standards Organization (ISO) specification was installed at an Arizona test facility (DPG site) in the winter of 1995/96. As part of the acoustic qualification of this site, comparative tests were conducted between this new surface, a Society of Automotive Engineers (SAE) sealed asphalt surface and an existing ISO surface in Michigan (MPG site). Initial testing with one vehicle and tire combination indicated that the new ISO surface produced ISO 362-1994 passby and coastby levels about 2 dB lower than sealed asphalt. Relative to the Michigan surface, the levels for the new Arizona ISO surface were 3 to 3½ dB lower. These differences were much greater than expected based on previously published studies of these two test surface types.