The shortest path is the path which is traveled in the shortest time in terms of time, with the minimum cost in terms of cost or in the shortest distance in terms of distance. Assuming the vehicle traveling at a constant speed, the shortest path can be regarded as the path takes the least time in other words the fastest path. Whereas, every time vehicles can not travel at a constant speed because of the road slope and horizontal curves. In this case, the fastest path can not be regarded as the shortest path. For the fastest path, calculations should be made taking into account slope of the roads and radius of the horizontal curves. In this study, a model was proposed to determine the fastest-the best route taking into account road slope, horizontal curve radius, road width, vertical road height and carrying capacity. For this purpose, first, study focused on factors affecting vehicle's speed, following formulas used for speed calculations of heavy vehicles on the vertical and the horizontal curved roads are explained. In determining the fastest route, to detect road sections that vehicle can not cross due to its climbing ability, cornering ability, width, height and loaded total weight, Geographic Information Systems (GIS) are employed.
