Formerly each railroad used its own cars exclusively, and through freights were transferred at every junction point. This involved such delay and expense that railroads now generally permit all loaded cars to go through to destination without transfer, and allow each other a certain sum for the use of cars. Usually this is about three-quarters of a cent for each mile which the car travels on a foreign road. This involves a great scattering of cars, and an extensive organization to keep record of their whereabouts and of the accounts between the companies for mileage.[15] This organization will be referred to more fully in connection with the department of transportation. But the joint use of each other's cars makes it necessary that there should be at least enough similarity in their construction and their coupling appliances to permit their indiscriminate use upon all roads. And conventions of master car-builders have recommended certain forms and dimensions as standards, which are now in general use. There is much convenience in this, but one disadvantage. It requires almost unanimous action to introduce any change of form or of construction, however advantageous it may be. And to secure unanimous action in such matters is almost as hard as it would be to secure unanimity in a change in the spelling of English words. Still there is progress, though slow, toward several desirable reforms, the most important of which is the adoption of a standard automatic coupler (see p. 142). Having shown how the property of all kinds is kept in efficient condition, we next come to its operation. This is called "conducting transportation," and the officer in charge is usually called the superintendent of transportation. All train-despatchers, conductors, train-men, and telegraph operators are under his immediate control. He makes all schedules and provides all extra and irregular service that the traffic department makes requisition for, himself calling upon the superintendent of machinery for the necessary locomotives, switching engines, and cars. It is his especial province to handle all trains as swiftly as possible, and to see that there are no collisions. It is impossible to detail fully the safeguards and precautions used to this end, but the general principles observed are as follows: First, a general time-table or schedule is carefully made out for all regular trains upon each division, showing on one sheet the time of each train at each station.