This report describes a full-scale experiment which examines the subjective response to riding comfort of a sample of over 600 private car drivers, driving their own cars over road surfaces of various standards of surface regularity. In this experiment, subjective impressions of riding comfort have been related in quantitative terms to an objective measure of ride represented by the root-mean-square (rms) vertical acceleration experienced at the person/seat interface. The relationship established, in the form of a 'comfort characteristic' curve, shows that, for a ride with an rms acceleration of less that 40 x 10 -3g, 95 per cent or more of the subjects rated the standard of ride as being 'acceptable or better'. For rms accelerations greater thatn 40 x 10 -3g, this proportion decreases almost linearly with the increasing rms acceleration. This relationship between comfort and rating and rms vertical acceleration could eventually form the basis of a proposed revised specification for road surface regularity in terms of the standard of riding comfort afforded by the surface.

A comparison of the responses obtained on rigid and flexible roads showed that, although similar acceleration levels were experienced, there was a greater probability , at the higher levels, that the assessment of ride on concrete surfaces would be less favourable.

The levels of acceleration experienced by the car-drivers showed no significant difference from those measured at the rear-seat position.

'Comfort characteristic' curves for male and female subjects show no differnce in subjective assessment of ride for the same levels of acceleration.

Future work will examine the standards of riding comfort in public transport and heavy goods vehicles and also investigate the causes of the observed differences found between flexible and rigid construction.

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