Seismic analysis is a conventional part of structural analysis (Chopra 2001). All of the finiteelement programs implement it as a basic function, and the effects of moving vehicles are always of special concerns in bridge engineering. Previously, vehicles were often approximated as moving loads, which in many cases allows a finite-element program to implement it without difficulties. But as increasingly larger vehicles are manufactured, bridges are subjected to larger and heavier loads so that the inertia effect of the vehicles can no longer be neglected. To consider this effect, various vehicle models were developed by researchers.