Heavy aerodynamic drag of ~70% among all drags is imposed on large bluff-based vehicles like buses and container trucks traveling at high speed. To reduce the drag, wake control experiments are performed with attention to effective utilization of under floor flow by using air guide vanes equipped at the based rear end corners. The aerodynamic drag is measured for a 1/16 bus model settled on the moving ground of a wind tunnel. The flow patterns controlled by the vanes are visualized by oil film and smoke tracer techniques. As a result, drag reduction of ~16% is successfully attained by optimizing the vane profile and position, in which the under floor flow is effectively induced by the under vane into the wake resulting in remarkable recovery of the negative pressure acting on the based end surface.