The object of the preset study is to make clear the generating mechanism of snow smoke behind trucks running in winter season, and to obtain the basic ideas to prevent the generation of snow smoke. Since the visualization experiments in a wind tunnel suggest that the large-scale vortices behind a truck generate the snow smoke, the spoiler generating three-dimensional perturbation was attached under the truck to suppress the evolution of the large-scale vortices. The three-dimensional perturbation was very effective to break up the large-scale vortices, and the spoiler was a useful device to prevent the snow smoke. The spoiler was installed to a model truck and an actual truck, and the effect of the spoiler was checked by driving tests. The results show that the spoiler is very effective to suppress the large-scale vortices behind the trucks.