In this paper the method, analysis, and results are presented of a study to determine the traffic noise field near and surrounding a highway tunnel portal. The purpose of the study was to determine how the increase in noise due to reverberations in a tunnel affects noise levels immediately outside a tunnel. An array of sound-level meters measured the traffic noise simultaneously at various locations near a tunnel portal. The results are given in terms of the statistical noise descriptors L10, L50, and L90. Graphic plots of distance from the tunnel portal versus decibel level are presented. Measurements were taken on top and in front of the tunnel portal. The results indicate that for measurement sites on top of the tunnel, the drop-off in sound level is very abrupt and at 30 to 40 ft (9 to 12 m) behind the portal the traffic noise has diminished to the ambient noise levels of the surrounding area. For sites in front of the tunnel portal, the drop-off rate is less abrupt than that for the sites on top but still rapid and reaches normal free-field traffic noise levels at 60 to 70 ft (18 to 21 m) from the portal.