For each of the three delivery locations, a separate PSD profile was created. Table 1 represents the overall Grms levels for each of the three delivery locations. Each of the PSD profiles (Figures 4-6) shows the results in power density levels versus frequency in the lateral, longitudinal, and vertical axes. The vertical axis produced highest overall Grms values of the three axes, and the inter-city delivery route had the highest overall vertical Grms value of 0.303.
The varying intensity of the Grms values reported in this study match closely with what other researchers have reported in previous studies of inter-city and highway delivery vehicles [5]. The higher Grms values of the inter-city location could be attributed to external sources such as road surface irregularities and repeated braking and forward acceleration [6]. These irregularities and repeated braking and accelerating happen much less frequently in the rural and highway delivery routes of this study resulting in lower overall Grms values.