The cost of conducting transportation is affected by the rate of grade of the road, the amount of rise and fall in it, and the length of the road. The rate of grade is important, because it limits the loads that can be hauled over the road, or determines the number of loads that must be made to transport a given weight of freight, as well as fixes a limit to the speed of travel. The amount of rise and fall affects the expenditure of power required to haul a load over the road. The length of the road has an effect upon the amount of work necessary to haul a load over it, the time required for a trip, and the cost of maintaining the road surface; each of which, other conditions being the same, is directly proportional to the length.
The cost of construction depends upon the accuracy with which the line of the road is fitted to the surface of the ground, as determining the amount of earth work and cost of bridges and culverts; upon the character of the ground over which the road is to be built, which affects the cost of executing the work and determines the necessity for and expense of drainage; and upon the cost of land for right of way. All of these
items must be considered in any comparison of the cost of constructing on various routes. Special care should be taken in selecting a line to avoid bad ground, such as swamps, upon which construction may be diffi cult and expensive. The availability near the line of the road of materials needed for surfacing may also become a matter of importance in the cost of construc tion, and have an influence in determining location.
The relative importance of the various elements affecting the choice of a line depends upon the nature and amount of the traffic to be provided for and upon the character of the road surface to be used. Where the traffic is heavy, the importance of reducing the cost of moving it by lessening grades and distance will be greater than where the traffic is light, and the cost of construction may be correspondingly increased for that purpose. If a smooth surface be employed, upon which traction' is light, the value of reducing grades will be greater and the value of reducing distance less than with a surface of poorer tractive qualities. .