It is interesting to compare the measured results in Figure 5 with the findings of a study conducted by Watts (7) in the United Kingdom. On the basis of measurements using a Mini Clubman Estate car, the following regression model between peak vertical acceleration and discomfort assessment was ob- tained by Watts:

x

0.20 + 4.28 aP for 0 ::s x ::s 6, r

2

.69 (1) where aP is the peak vertical acceleration in units of g and x is the discomfort score rated by test subjects the basis of the following scale:

0

comfortable,

2

slightly uncomfortable,

4

uncomfortable, and

6

very uncomfortable. The data in Figure 5 imply that most drivers would not cross a hump faster than a speed that causes a peak vertical acceleration in the region of 0.7 to 0.9 g. According to

Equa

tion 1, this acceleration range corresponds to discomfort scores between 3.2 and 4.1, which is in the "uncomfortable" range. The minimum recorded acceleration of 0.43 g corresponds to

x

1.9 or "slightly uncomfortable," whereas the maximum value, 1.08 g, corresponds to

x

4.8, which is between "un- comfortable" and "very uncomfortable. " The distribution of acceleration data in Figure 5 therefore appears to be in good agreement with the findings of the U.K. study