Time of day noise adjustments or "penalties"

Community response descriptors, such as Day-Night Average Sound Level (DNL), have included a nighttime adjustment or ‘‘penalty’’ in their formulation. Typically this nighttime penalty has been 10 dB. Some models incorporate an evening penalty in addition to the nighttime penalty. The basis for these penalties is examined in this paper. This analysis is based on results from a community attitudinal survey conducted in the vicinity of a large Army base. The survey sought to compare blast noise (e.g., artillery) and helicopters in the context of all noise such as airplane, traffic, and children. The analysis shows that there are at least two factors which contribute to a ‘‘penalty’’ during any time period. One factor occurs when individual events are intrinsically more bothersome or annoying during one period of time than during another time period. The second factor occurs because a greater percentage of events are most likely to be noticed and found bothersome during one period of time as compared with another. The results show that single bothersome events are more or less equally annoying during all time periods of the day. There is only a small growth in annoyance during the night and this growth occurs primarily with the more impulsive sources such as artillery and helicopters. The results indicate that the second factor described above is more important in contributing to a total nighttime adjustment of penalty. That is, for a given number of available events, respondents are more likely to notice and be bothered by events during the night than during the day. This factor appears to be a primary contributor to any nighttime adjustment. The nighttime penalty indicated by these two factors is of the order of 5 to 10 dB. These results tend to support retention of a nighttime penalty in descriptors such as DNL. Based on the results, one would not be tempted to depart from the long-established 10-dB value for the penalty.