Vibration from bus is transmitted to passenger's body mainly through three portions: seat's lazyback, seat's support surface, and passenger's feet, respectively; many scholars have a lot of research works in human body vibration, especially Michael Griffin and his teams.
During the evaluation of comfort, the criterion specifies that not only the three-direction linear vibration of the three portions, seat's lazyback, seat's support surface, and passenger's feet, respectively, but also the three-direction angular vibration of the seat's support surface should be considered; that is, there are a total of 3 points of vibration input and 12 axial vibrations should be calculated in order to completely describe the vibration.