Experiences of upright sleeping in a vehicle: the preferred back rest angle

Abstract: In many vehicles passengers are sleeping. Groenesteijn et al.(2014) reported that on medium to long distance train trips, the second most time was spend on ‘staring or sleeping’. Bouwens et al. (2017) report that the majority of passengers sleep during a flight, while this activity has the lowest comfort score. The likelihood of resting and sleeping during a commute automated vehicle trip is also high (Wilson et al., 2022). Usually this sleeping is a nap, as Faraut et al. (2017) defined a nap as any sleep period with a duration of less than 50% of the average major sleep period of an individual. Discomfort while taking this nap might be caused by the upright sitting position. Studies by Nicholson and Stone (1987), Aeschback et al. (1994), Hayashi and Abe (2008) and Roach et al. (2018) show that the larger the recline angle of the seat ('flatter'), the better the sleep efficiency. A flat bed is preferred. However, a flat bed is often not possible due to space and economic reasons. In this study we tried to discover what back rest angle is acceptable for an upright sleep. The study was carried out using six customized chairs of which the backrest could be positioned in five different angles (110º, 120º, 130º, 140º, 150º) and an additional 180º bed was added as a reference (a horizontal stretcher). Sleeping was facilitated by for instance, a good temperature, darkness, blankets and cushions. 16 participants were asked to try to sleep six times for a duration of 90 minutes to facilitate at least one sleep cycle, each person starting in a different backrest angle and having a different order. Questions on sleep comfort and comfort in general (on a scale 0-10, 0 being no comfort and 10 extreme comfort) were asked after the sleep. The results show that overall comfort was low (below 6) for 110 and 120 degrees and it was significantly better at 130 degrees or more. The same trend was shown for the sleeping comfort. In conclusion, a conclusive statement based on sleep quality is hard to give, but in terms of comfort a backrest angle of 120 degrees or less is unacceptable for a nap. Suggesting that for a short napping situation a minimum of a 130 degree recline should be available. To improve sleep comfort in 110 and 120 degree recline; neck support, lower back and lower leg support are the main attention points.

Keywords: sleep, mobility, Comfort, napping, backrest

DOI: 10.54941/ahfe1005258

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