TNO is investigating the impact of night-time traffic noise on sleep. Overall the results of the study indicate that people living in the vicinity of busy motorways, urban access roads, provincial roads, and - during the night-time - busy railways sleep poorer compared people living near quieter streets.
From November 2004 to May 2005 TNO carried out a major study in twelve residential areas of cities and villages. In the study 262 adult subjects (between 18 and 80 years of age, 55% women) participated for six nights and five days (1572 subject nights). Subjects wore actimeters to monitor motility during sleep and to register self-reported awakening. Noise monitors measured sound levels per second during each study night from 22:00 till 09:00 hours outside and inside the bedroom of each subject.
The results show a consistent pattern. Motility and self-reported awakening increase, whereas perceived sleep quality decreases with increasing road and railway noise exposure indoors during sleep. In contrast to common believe, the results show that people do not get completely physically accustomed to night-time traffic noise.
A study that incorporates the data from the major study referred to above has recently been completed into the reaction of the autonomic nervous system during sleep to noise caused by road and rail traffic. The results show that this part of the nervous system, which promotes rest and recovery, is less active during sleep when traffic noise exposure is high. Normally during sleep this resting activity of the nervous system remains relatively high, which is important for recuperation. Further research is needed to investigate the long-term effects on health.