This study aims to determine the optimal winter speed limit through the application of a cost analysis and by analysis of effects of road and traffic conditions. Initially, a cost analysis of travel time costs, vehicle operating costs, pollution costs, and accident cost was applied to determine optimal average speed on the basis of the minimum total cost. Then, the effects of road and traffic conditions were calculated by regression analysis. Finally, the optimal winter speed limits were achieved. In conclusion, we found that our model was reliable and the results were appropriate and sustainable for the long term.