Sleep disturbances caused by vibrations from heavy road traffic.

The influence of whole-body vibrations, noise, and a combination of the two, caused by heavy road traffic (150 events/night) on sleep, subjectively experienced sleep quality, and performance was investigated under controlled laboratory conditions for male and female subjects 20-35 years of age. A room was built above a vibrator table, with the legs of the bed mounted directly on the table through holes in the floor. Vertical vibrations were found to be attenuated by the mattress with 20-40 dB for frequencies greater than 10 Hz, whereas horizontal vibrations were slightly amplified. It could be concluded that when traffic noise [50-dB (A) peak level] is accompanied by vibrations with peak levels of 0.24 m/s2 vertically and 0.17 m/s2 horizontally as measured on the frame of the bed (stimulus duration approximately 2 s, dominant frequency approximately 12 Hz), sleep is more disturbed than is the case when noise alone occurs. The amount of REM sleep, which was significantly reduced for the vibration level mentioned above, was even more disturbed when a higher exposure level, 0.34 m/s2 vertically and 0.24 m/s2 horizontally, was applied. The subjectively rated sleep quality was lower for the higher than for the lower vibration level. Performance in the morning was only influenced for the higher vibration level. It could be concluded that vibration exposure levels near the recommendation made in ISO-standard 2631 for the awake state disturb sleep in man.