Approximately 270 noise-level recordings were obtained at 39 highway sites and compared with the noise-level predictions obtained by the procedure outlined in NCHRP Report 117. The measured noise levels were computed in terms of the A-weighted L10 value (level exceeded 10 percent of time) and then compared to the predicted noise levels. A significant discrepancy was found between predicted and measured noise levels; generally, the predicted values exceeded the measured values. Average error per location was 4.8 dBA; the maximum error was 13 dBA. A nomograph was devised to correct the predicted value; this nomograph involves observer-to-roadway distances, truck volumes, and automobile speeds. By applying correction factors, the average error was reduced to 1.9 dBA, a 60-percent reduction in error. Based on these findings, the nomograph was approved by the Federal Highway Administration for use in predicting noise levels in Kentucky.

Report Date


Report Number

No. 409

Digital Object Identifier



Accepted for publication by the Transportation Research Board.