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Year : 2002  |  Volume : 4  |  Issue : 15  |  Page : 65--67

Sleep studies before and after - results and comparison of different methods

Evy Ohrstrom 
 Department of Environmental Medicine, Göteborg University, Göteborg, Sweden

Correspondence Address:
Evy Ohrstrom
Department of Environmental Medicine, Göteborg University Box 414, SE-403 50, Göteborg


The effects of long-term exposure to road traffic noise on sleep quality were assessed using questionnaires and acetimetry. Results obtained before and after reduction in road traffic were compared. Sleep quality was improved after the reduction of noise levels. There was some correlation between acetimetry parameters and subjective parameters.

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Ohrstrom E. Sleep studies before and after - results and comparison of different methods.Noise Health 2002;4:65-67

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Ohrstrom E. Sleep studies before and after - results and comparison of different methods. Noise Health [serial online] 2002 [cited 2020 Sep 26 ];4:65-67
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The objectives were to assess: (1) effects on people of long-term exposure to road traffic on sleep quality using various methods and (2) how people's sleep quality was affected by the changed traffic situation.


The area of investigation was divided into an exposed and a control (less exposed) area. The houses were situated less than 70 meters and 125 - 400 m respectively from the trafficked main road. A first study was performed in 1997 before the opening of the new tunnel for road traffic. The main follow up study was performed in 1999 after noise reduction as a result of tunnel use.

A main questionnaire was used for evaluation of various adverse health effects including questions on how you usually sleep. A second questionnaire (sleep log) for daily reports of sleep was completed during 3 consecutive days. A smaller sample also took part in a sleep study with registration of body movements by actigram during 3 nights.


In total 142 participants answered the general questionnaire, 116 answered the 3-day sleep log and 26 participants took part in the acetimetry study. For various reasons not all of the original participants were able to take part in the follow up study. The average age was 51 years in both areas, ranging from 18 - 75 years of age. There was no difference in age, sex or time of residence between those who answered the general questionnaire and those who answered the sleep logs. The acetimetry sample was matched according to age for both men and women. The age varied from 24 to 68 years of age.

The total number of vehicles decreased from about 25 000 to 2 400 from 1997 to 1999. During the night-time there was a decrease from about 1400 to 550 vehicles. Noise levels in LAeq on the noisiest side varied between 56 and 69 dB and decreased with about 10 dB on average in the less-exposed area. The night-time noise level was about 5 dB lower. In addition, the majority of people had their bedrooms on the less noisy side, giving a further 5 dB lower noise level.

Sleep quality - General questionnaires vs. controls

Results from the general questionnaire reveal that sleep quality was significantly worse in the exposed area in terms of time needed for falling asleep, awakenings, sleep quality and alertness in the morning. Also a higher percentage of people in the exposed area closed their bedroom windows at night compared with those in less exposed areas (45% and 20 % respectively).

Changes in sleep quality in the exposed area after changes in noise exposure

Significantly fewer participants slept with closed windows after noise reduction. The percentage with a long sleep-latency decreased and participants felt more alert in the morning.

Awakenings and sleep quality were somewhat, but not significantly improved. Between 20 and 30% of the participants reported improvements in their sleep in various ways.

Sleep quality - comparison of information from questionnaires and sleep logs

Sleep quality based on the general questionnaire was compared with results in the sleep log that was answered for 3 days. The values in the sleep log differ slightly from the general questionnaire, however the difference is only significant in one case.

Sleep quality of a sub-sample in the exposed area based on acetimetry

There were large inter-individual differences for the various acetimetry parameters. After noise reduction a significant, and unexpected, decrease in time in bed and sleep minutes was observed. Sleep latency, mean activity and wake minutes were, however, not significantly affected, although there was a tendency towards an increase in sleep latency.

Sleep quality of a sub-sample in the exposed area based on questionnaires

For sleep minutes we see a significant decrease (on average 50 minutes less) after noise reduction which is in accordance with the acetimetry results. There is also a significant, unexpected increase in estimated movements. Participants felt significantly more alert in the morning and tended to have less difficulty falling asleep and to have better sleep quality. Sleep was therefore more efficient after noise reduction.

Correlations between acetimetry and sleep log parameters

There were significant correlations between acetimetry parameters and subjective parameters. Some correlations were expected to be significant, for example sleep minutes since this is strongly related to time in bed after lights out to getting up in the morning. Sleep quality was also significantly related to activity, wake minutes and number of wake periods. Subjective sleep latency was however not correlated with acetimetry based sleep latency.

Awakenings were not related to wake periods or even to number of wake periods longer than 5 minutes (which you are expected to be able to remember).


Sleep quality is significantly reduced by exposure to road traffic at noise levels below 60 LAeq outdoors at night and sleep quality can be improved by an extensive reduction in noise levels. Sleep quality assessed as "usual sleep" by single questionnaires may give equally good precision as daily reports on sleep over several days and a higher response rate is achieved by a single questionnaire. Some perceived sleep quality parameters are significantly related to acetimetry parameters. However, due to large inter-individual differences, studies performed by acetimetry must include a relatively large number of participants or a rather homogenous study population.[3]


1Ohrstrom E, Agge A and Bjorkman M (1998). Sleep disturbances before and after reduction of road traffic noise. Noise Effects ´98. Proceedings of the 7th International Congress on Noise as a Public Health Problem Sydney Australia 22-26 November 1998, Volume 2, pp 451 - 454.
2Ohrstrom E och Skanberg A_B (1999). Konsekvenser av Lundbytunneln. Del I: Undersokningar av storningsupplevelse, somn, halsa och valbefinnande hos befolkningen vid Vastra Brackevagen, Goteborg. Del II: Fordjupade somnundersokningar. Report 4/99, Department of Environmental Medicine, Goteborg University. In Swedish.
3Ohrstrom E (2001) Adverse health effects before and after reduction in road traffic. In: Proceedings 17th International Congress on Acoustics. Rome 2001, September 2-7. CD-format, Abstract book p 108.