Intermittency ratio: A metric reflecting short-term temporal variations of transportation noise exposure

Abstract

Most environmental epidemiology studies model health effects of noise by regressing on acoustic exposure metrics that are based on the concept of average energetic dose over longer time periods (i.e. the Leq and related measures). Regarding noise effects on health and wellbeing, average measures often cannot satisfactorily predict annoyance and somatic health effects of noise, particularly sleep disturbances. It has been hypothesized that effects of noise can be better explained when also considering the variation of the level over time and the frequency distribution of event-related acoustic measures, such as for example, the maximum sound pressure level. However, it is unclear how this is best parametrized in a metric that is not correlated with the Leq, but takes into account the frequency distribution of events and their emergence from background. In this paper, a calculation method is presented that produces a metric which reflects the intermittency of road, rail and aircraft noise exposure situations. The metric termed intermittency ratio (IR) expresses the proportion of the acoustical energy contribution in the total energetic dose that is created by individual noise events above a certain threshold. To calculate the metric, it is shown how to estimate the distribution of maximum pass-by levels from information on geometry (distance and angle), traffic flow (number and speed) and single-event pass-by levels per vehicle category. On the basis of noise maps that simultaneously visualize Leq, as well as IR, the differences of both metrics are discussed.

Classification of Urban Road Traffic Noise based on Sound Energy and Eventfulness Indicators

“…As explained in Section 2.1, the microphone was placed close to the road to reduce the influence of noise from other sources and, therefore, the source-receiver distance was not always the same. This factor influences the IR values ( Figure 4 in [12]).…”

“…where C, as stated in [7], can be assumed equal to 3 as a result of the numerical simulations for different traffic situations;…”

“…It can be derived either directly from acoustic measurements or calculated from traffic and geometric data for any transportation noise source and any time period. However, as pointed out in [7,8], IR could be a supplementary metric accompanying the continuous equivalent level (L Aeq ), which measures the energy content of the noise exposure.The present paper starts from the results obtained in a previous application of IR on the noise data from road traffic, monitored continuously for 24 h in 90 sites in the city of Milan [8,9]. The database comprised 251 24-h long time series of 1 s A-weighted SPL, monitored at different types of roads, from motorways to local roads with very low traffic flow.…”

“…It can be derived either directly from acoustic measurements or calculated from traffic and geometric data for any transportation noise source and any time period. However, as pointed out in [7,8], IR could be a supplementary metric accompanying the continuous equivalent level (L Aeq ), which measures the energy content of the noise exposure.…”

Validation of large scale noise exposure modelling by long-term measurements

“…On that basis, typical noise exposure metrics such as L Day , L Night , L Evening , and L DEN were derived. In addition to such noise exposure levels based on the Leq, the concept of the Intermittency Ratio (IR) was applied, a metric characterising the temporal variation of a noise exposure situation [36]. IR was evaluated for each façade point on an hourly basis as well as integrally for day and night-time.…”