Conversions between noise exposure metrics 24-hour Leq, Ldn, and Lden: the impact of diurnal local bus traffic patterns on population annoyance in the United States

Noise during evening and nighttime hours tends to be associated with high annoyance, which is reflected in the use of community noise exposure metrics, such as the Ldn and Lden, that include penalties during these hours. Transportation noise sources may exhibit distinct diurnal patterns, but the impact of these patterns on different noise metrics has not been thoroughly evaluated, especially within the United States. In this study, we utilized General Transit Feed Specification (GTFS) data from 24 major cities in the U.S. to quantify diurnal traffic patterns for local buses, and the impact of these patterns on differences in noise metrics, such as LDay, LEvening, LNight, Ldn, and Lden, compared to the 24-hour LAeq24, Using mathematical conversions between the noise metrics, we found on average across the cities that the Ldn was between 2.8 to 3.6 dB higher than the LAeq24, and the Lden was also 3.6 to 3.8 dB higher than the LAeq24 for noise from local buses. This increase was mainly due to noise during daytime (LDay) that was higher than the 24-hour average noise, and dB penalties added to the Ldn and Lden metrics, which compensate for less bus traffic during evening and nighttime hours. We discuss the relevance of these conversions and the observed differences between the 24-hour LAeq24 and the Ldn and Lden, which are used for health impact assessments of high annoyance, on public transportation planning.