Water Terminals

The average freight car earnings per year in America are approx imately $2,200. The average life of a freight car is from 20 to 25 years. To whatever extent the unproductive weight of a train can be diminished, to that extent the productive weight may be increased by the absorption of the same amount of energy of locomotive tractive power without reduction of the rate of speed. The expenditure of fuel in hauling a ton is about the same whether or not it is paying freight. The smaller the percentage of non paying or dead weight to total weight moved, the smaller will be the cost of hauling the paying freight.

On American class I railroads the cost of hauling one ton of dead weight I mile varies from $0.004 to $0.007. The cost of hauling a ton of weight is not directly proportional to the weight carried but rather the relation of the full tonnage possibilities to actual tonnage hauled. A railroad having full tonnage trains will have a lower cost per ton-mile than one with variable loads of less than full tonnage.

Great progress has been made by American railroads in the standardization of freight equipment. The following table shows a comparison of a few representative car parts necessary to keep on hand at railway shops for repairs and represents the progress made in standardization in 41 years.

Car Trucks.

Car trucks in use on American railways are built in accordance with general requirements specified by the American Railway Association. The cast iron wheel 33 in.

diameter, with a chilled tread, is in use under freight cars of a capacity of 5o ton and under. On nearly all passenger equipment and on a few freight cars of high capacity steel wheels are used. For 1929 the side frames of all new freight car trucks are commonly of cast steel. Pedestal type trucks are used for pas senger equipment and to a limited extent for freight equipment.

Tractive Resistance

of freight and passenger cars is very important because of its relation to tonnage ratings of locomotives and to questions of economies of operation. The resistance of a car to movement on a straight level track may be divided into the following components: (a) journal friction, (b) rolling of the wheel on the rail; track resistance due to compression of the track, concussions, and miscellaneous losses due to oscillation and vibration that absorb energy from which no return can be ob tained; (c) flange friction due to the pressure of the wheel flange against the rail; (d) atmospheric resistance; still air and wind.

Plain bearing friction varies within certain limitations of speed while roller bearing friction is fairly constant from zero up to high speeds. Rolling of the wheel on the rail and the flange friction increase with the speed and also vary materially with the condition of the track and stiffness of the rail. The atmospheric resistance increases as the square of the speed. Rolling of the wheel and flange friction are reduced to a minimum by the use of heavy rails well supported and with proper alignment.

Container Car.

The container car system is now coming into popular use on American railroads. This system provides that portable containers shall be loaded and locked at the ship per's own plant, conveyed by motor truck to the railroad yard and lifted by crane aboard the container car where steel bulk heads and sides form absolute protection against opening the container in transit. At its destination the locked container is unloaded by crane and carried by motor truck directly to the warehouse or consignee's door to be unloaded at his convenience. One of the principal advantages of the container car system is the greatly increased use of container car rolling stock in moving service which is particularly important when traffic expands to its "peak" and the prime need is to shorten layovers of cars in yards and stations for loading and unloading and to limit their idleness and obstruction through misuse for storage purposes.

(See American Society Mechanical Engineers, paper by Walter C. Sanders presented at annual meeting, New York, Dec. 6, 192!) Refrigerator and Heater Cars.—The need for protection in transit against all ranges of temperature of such commodities as meat, milk, fruit and vegetables, has led to the design of va rious types of refrigerator and heater cars. A large number of refrigerator cars are designed for both passenger and freight train operation. Some cars used for transporting semi-perishable com modities not requiring refrigeration or heating are insulated and ventilated to protect the loading against extreme outside tempera tures and the heat of the product itself. The principal means of obtaining refrigeration in transit is by circulated air, cooled by contact with ice, or mixtures of ice and salt. Some modifications of this system and others differing radically such as mechanical refrigeration or iceless cars are in use to a small extent and may be more generally adopted in the future.