Noise from highway vehicles emanates primarily from engine exhausts, tire-pavement interaction) gears, and rattles. Studies have shown that at high speeds tires become the dominant generators of noise. Measurements on different road surfaces have produced different noise-versus-speed relationships (1). This led to the road surface adjustment used in the noise prediction procedure developed in NCHRP Report 117 (2). This adjustment called for a 5 dBA reduction for smooth surfaces (very smooth, seal-coated asphalt pavement) and a 5 dBA increase for rough surfaces (rough asphalt pavement with voids 1/2 inch (12 mm) or larger in diameter and grooved concrete). There was no adjustment for normal surfaces (moderately rough asphalt and concrete pavements).

The surface descriptions are vague, and it is left to the discretion of the user to apply adjustments where applicable. Consideration was given initially in this report to ''rough" surfaces, but the term was abandoned because it seemed vague and maybe misleading. Also, various degrees of roughness gave a wide range of noise levels. In fact, it appears that the terms "smooth", "normal", and "rough" address only that portion of tire noise generated by drumming or percussion of the tire against knobs in the pavement surface. "Smooth" does not distinguish "smooth and dense" from "smooth and porous". It has been argued that the -5 dBA adjustment should not be used since some truck tires become excessively noisy on very smooth surfaces and inasmuch as such surfaces are presumed to be ready for renewal because of their inherent low friction characteristics (3). Minimum noise is believed to be associated with smoothness and an optimum porosity. In this report, surfaces are identified according to Kentucky specifications.

Noise data were taken on all major types of surfaces presently used in Kentucky. A reference automobile was used to determine any difference in noise. Strip-chart records were made to evaluate the effect road surface type had on the noise of the entire traffic stream.

Report Date


Report Number

No. 452

Digital Object Identifier



Accepted for publication by the Transportation Research Board.