Driver discomfort in vehicle seats: effect of changing road conditions and seat foam composition

Discomfort in vehicle seats is a multi-factorial problem with contributions occurring from effects of sitting duration, seat design, and the dynamic environment to which the occupant is exposed. This paper reports laboratory studies investigating the extent to which reports of discomfort are affected by vibration commencing or ceasing, and whether methods of assessment are sensitive enough to detect small changes in foam composition. Study 1 measured discomfort ratings for two conditions of 60 minutes each, comprising 30 minutes of vibration exposure followed by 30 minutes of static sitting in a car seat, and vice-versa. Study 2 measured discomfort ratings for three conditions over a period of 40 minutes each, whilst participants were sitting in one of two car seat compositions, and either exposed to vibration or not. In both studies participants operated a driving simulator. It is shown that exposure to vibration increases the rate of discomfort onset in comparison to periods of static sitting. When vibration stopped, there was an acute improvement in comfort but discomfort did not drop to the levels reported by those who had been unexposed. When vibration started after 30 minutes of static sitting, there was an acute increase in discomfort but not to the levels reported by those who had been exposed to 30 minutes of vibration. After 40 minutes of continuous exposure it was possible to detect significant differences in overall discomfort between the two seat compositions, although trends could be observed in less time.