Taking a nap is a welcome pastime in vehicles such as trains, airplanes, and cars. Flat sleeping cannot always be facilitated because of space and economic constraints, but a larger backrest recline angle is associated with better sleep quality. To define the best and the worst comfort experience and sleep comfort in these settings, and to offer design guidelines to practitioners, six backrest recline angles were compared regarding overall comfort and sleep comfort. The backrest recline angles ranged from 110 to 150 degrees, and 180 degrees was added as a reference. 16 participants were invited to sleep for a duration of 90 min. in each condition. Overall comfort and sleep comfort significantly improve in conditions higher than 120 degrees. Local discomfort is rated relatively low in all angles, but in comparison, people experience high discomfort in the neck, lower back, and lower leg region while in the 110 and 120 degrees condition. It is concluded that in the bigger recline angles the napping comfort experience is higher, with a minimum advised angle of 130 degrees.@en

As the automotive industry advances towards greater autonomy, the landscape of car travel is evolving. The integration of reclined seating within vehicles, made possible without major alterations to traditional layouts, presents a promising avenue for enhancing passenger experiences. This shift, however, comes with unique safety challenges due to the changed seating dynamics.
Research, including insights from General Motors, Volvo & Volkswagen emphasizes the need for innovative safety solutions for reclined seating. Simulations comparing three-point and four-point seat belt configurations, in both upright and reclined positions, reveal advantages for the latter at higher speeds. This configuration produces a more balanced force distribution during impacts, away from vital areas.
While the potential of a four-point restraint system is evident, implementation hurdles arise. Addressing both safety and comfort, a study assesses the user experience for both systems. Building on these insights, a convertible restraint system is proposed, seamlessly transitioning from a three-point to a four-point configuration based on passenger position. This adaptable design merges safety and comfort effectively.
The proposed design requires the redesign of certain components of the seat back & headrest. These are provided as recommendations.

As the automotive industry advances towards greater autonomy, the landscape of car travel is evolving. The integration of reclined seating within vehicles, made possible without major alterations to traditional layouts, presents a promising avenue for enhancing passenger experiences. This shift, however, comes with unique safety challenges due to the changed seating dynamics.

Research, including insights from General Motors, Volvo & Volkswagen emphasizes the need for innovative safety solutions for reclined seating. Simulations comparing three-point and four point seat belt configurations, in both upright and reclined positions, reveal advantages for the latter at higher speeds. This configuration produces a more balanced force distribution during
impacts, away from vital areas.

While the potential of a four-point restraint system is evident, implementation hurdles arise. Addressing both safety and comfort, a study assesses the user experience for both systems. Building on these insights, a convertible restraint system is proposed, seamlessly transitioning from a three-point to a four-point
configuration based on passenger position. This adaptable design merges safety and comfort effectively.

The proposed design requires redesign of certain components of the seat back & headrest. These are provided as recommendations

The sleep quality and (dis)comfort sitting upright was studied among 40 participants who took a nap at home. They were asked to take a nap at 17:00h on three consecutive days. The backrest had to be at a different angle every day: upright, reclined and more reclined. They were asked to record the backrest angle of the three positions and report the length of the sleep, the sleep quality, comfort and discomfort and influence of other factors each during each nap. From the 120 cases (3 conditions, 40 participants), the cases where participants were not able to sleep had an average backrest angle of 110˚, which was significantly different from the cases where participants were able to sleep, who had an average backrest angle of 118˚. The scores in the more upright position (<110˚) resulted in significantly more discomfort and a lower sleep quality than in the reclined positions (>123˚). As the conditions were arranged by the participants, there was much variation in outcomes. Therefore, future research under more standardised conditions is recommended.@en