Sleep disturbance due to environmental noise: A proposed assessment index

Traditional methods of assessing the impact of environmental noise are generally based on the use of "equal-energy" measures of noise exposure, such as LAeq,24hr or ANEF. These have been derived from studies of the annoyance generated by the noise. This paper presents a proposed methodology for directly assessing the level of sleep disturbance due to intermittent night-time noise, independent of the degree of annoyance caused. The procedure is based on calculation of a Sleep Disturbance Index (SDI) which is numerically approximately equal to the average number of awakenings per night due to the noise. Typical values of SDI would range from less than 0.2, representing a relatively insignificant level of disturbance, to greater than 5, representing a very high level. Details of calculation procedures, and possible criterion values in terms of SDI, are discussed. The use of this methodology in addition to traditional "equal-energy" noise indices should allow for a more comprehensive assessment of the impact of night-time noise on residential communities