Abstract: In the method an existing surface of a bearing course (120) of a traffic route is first chosen as the reference level (100), in relation to which the target level (150) of a surface of a bearing course to be formed is determined. After this the forming procedure of a bearing course is performed, in which the surface of a bearing course is brought to the target level. Typically the forming procedure comprises spreading, levelling and compacting of a soil layer on the surface of the reference level. The location of a traffic route is determined in the terrain as plane coordinate points (xn, yn) with a satellite positioning method and the elevation zn of an existing bearing course chosen as the reference level is determined in each coordinate point (xn, yn) as cross sectional figures extending from the unchanged terrain on the first side of the traffic route over the surface of the traffic route to the unchanged terrain on the second side of the traffic route.