The presumed relationship between driving comfort and vehicular vibrational levels has not been adequately addressed. Driving simulators now permit experimental means of evaluating hypothesized relationships between the two. The paper describes preliminary results of such a study.Two numerical methods of evaluating the vehicular vibrational levels are discussed. The first, the ISO method, analyzes the vibrational frequency spectra and, by means of a filtering process, yields partial, effective values which, when multiplied by the frequency response of the filter, produce total, effective values. The second method, developed from recent studies, correlates frequency values which are found to be equally stimulative to human perception. This treatment leads to calculation of duration times of toleration of vibrations and subsequent evaluation of loss of operating ability by drivers. Both of these two methods are then incorporated into an optimization program which gives two differing sets of optimum shock absorption characteristics for roadways.Tests were conducted with drivers in a simulator which requires driver operation under vibrational loadings. Preferred shock absorption levels were identified by the subjective reactions of the participants. Results showed good agreement with those predicted by the second vibrational evaluation method.