Effects of traffic noise on quality of sleep: assessment by EEG, subjective report, or performance the next day.

Twelve people living in areas of high traffic noise were studied to assess its effect on their sleep. During 3 weeks, their sleep was monitored physiologically in the natural setting of their own bedrooms. Their performance and subjective report of sleep were recorded each day. For the middle week, the bedroom windows were double glazed to reduce the prevailing level of traffic noise at the bedside [Leq 46.6 dB(A) over the whole night] by an average of 5.8 dB(A). Most physiological measures were unaffected by the noise reduction, but stage 4 sleep and low-frequency, high-amplitude delta waves in the EEG, both thought to be signs of deep sleep, were increased. Also unprepared simple reaction time, a test sensitive to drowsiness, was improved the next day, whereas a more stimulating short term memory test was not. Subjects also reported sleeping better. These improvements with double glazing were all modest in degree, but as they occurred in three independent and predicted measures of sleep quality, the view is supported that the prevailing level of traffic noise does indeed impair sleep.