Evolution of rate sheets, 101.--Terminal v. haulage costs, 102.--Local competition, 104.--What the traffic will bear, 107.--Trunk line rate system, 111.--Complexity of rate structure, 113.--Competition of routes, 114.--Competition of facilities, 116.--Competition of markets, 118.--Ever-widening markets, 119.--Primary and secondary market competition, 121.--Jobbing or distributive business, 124.--Flat rates, 127.--Mississippi-Missouri rate scheme, 128.--Relation between raw materials and finished products, 134.--Export rates on wheat and flour, 135.--Cattle and packing-house products, 139.-- Refrigerator cars, 140.--By-products and substitution, 142.--Kansas corn and Minnesota flour, 143.--Ex-Lake grain rates, 145.-- The task of constructing a freight or passenger tariff is an eminently practical one. The process must be tentative and experimental. Little can be calculated in advance. Tariffs are not made out of hand; they grow. Not until a rate has been put into effect, can its results be known. The lower limit of charges, however, is more or less fixed. Obviously the rate must not be less than that portion of the variable expenses incident to each particular unit of business. This variable expense is divisible into two parts, one for loading and unloading, and the other for actual movement. The first step in constructing a tariff, therefore, is to separate these two portions of the variable outgo. General experience fixes the terminal outlay for loading and unloading at an average figure of about twenty or twenty-five cents per ton at each end of the line; that is to say, at an average of about two and one-half cents per hundred pounds as the total terminal cost.[64] Just where, above or below this average, the figure for any particular tariff will lie, depends upon a multitude of details. This terminal expense is obviously quite independent of the length of the haul. It costs no more to load for a carriage of 3,000 miles than for one between two adjoining stations. It is the second portion of the specific costs, namely, the movement expense, which varies with the distance. This movement cost is more difficult of determination, as affected by a multitude of variable factors, such as the grades, curvature, number of stops, the size of train load, and above all, the volume of the traffic. Assuming the simplest physical conditions, one would expect the movement expense, aside from the initial cost of getting up steam in order to move at all, to rise proportionately to the distance traversed. Graphically represented, the tariff would appear somewhat as follows: [Illustration: Relation of Cost of Carriage to Distance.]