L10 versus Leq—A User's Perspective

The Federal Highway Administration (FHWA) regulation tor highway traffic noise analysis, FHPM 7-7-3, allows for the use of either L10 (sound level exceeded 10 percent of the time) or Leq (energy equivalent sound level). Therefore, state highway agencies have the responsibility to empirically determine the preferable descriptor (L10 or Leq) for typical highway projects. As such, the New York State Department of Transportation (NYSDOT) has performed several such studies in recent years. Among those are an analysis of two major prediction methodologies (National Cooperative Highway Research Program (NCHRP) Reports 117 and 174), and a long term measurement study of the Youngmann Expressway Noise Abatement Project in Buffalo, N.Y. Results of these two studies indicate that both L10 and Leq are satisfactory descriptors for proposed highway projects. However, for vehicular flow rates of somewhere less than 400 automobiles per hour, L10 becomes suspect because the assumption of equal vehicular spacing becomes non-valid. For long-term studies, Leq is very sensitive to equipment malfunction, but is superior to L10 in its ability to consider short duration, random occurrences.