A large number of passenger train cars were in 1928 equipped with roller bearings and all modern cars are now roller bearing equipped. Practically all of the new designs of the electric cars are fully roller bearing equipped. These applications exist not only on the journals but also on the armature shafts of the motors and in the speed reduction units. Roller bearings have also been applied to freight cars, locomotive tenders, driving axles, engine trucks and trailing axles. A roller bearing equipped train can be started with one-eighth the power required to start a train equipped with plain journals.
For a discussion of Electric Motor Cars and Self Propelled Equipment see ELECTRIC TRACTION ; LOCOMOTIVES.
An articulated car consists of two or more car bodies flexibly coupled together and operating as a single unit by necessity of its truck arrangement. Each articulation or joint in the car is supported by only one truck. The number of trucks is one more than the number of bodies permanently coupled. The use of articulated cars in America is limited mainly to elevated and subway service in cities, to electric railway cars and to self-propelled rail motor cars, as the articulated principle must be used in trains kept as one unit during their entire trip.
Rolling stock for use in handling freight in America are termed "freight cars" and are divided into several general classes. The cars generally in use are of either the enclosed type, which includes box, refrigerator, stock and other house cars; or of the open type which include flat cars, gondolas, both high and low side, hopper and other cars of open construction. Tank cars for conveying oil and other liquids in bulk are used; as are also many types of special cars.
The operation of freight cars on American railroads has resulted in the adoption of certain fundamentals of design which experience has shown to be the most practicable. (See "Standards and Recommended Practices" and "Supplement," American Railway Association.) The materials that are used in the construction and maintenance of freight and passenger train cars may with few exceptions be divided into four general classes, as follows : (1) metal materials ; (2) lumber ; (3) paints and varnishes ; (4) various complete devices or specialties. The re quirements to be met in the design of freight rolling stock are protection of the contents (when required) from weather; facili ties for loading, packing and unloading ; strength of underframe and body to withstand severe service, and the largest available capacity consistent with requirements of construction.
In the early days of development freight cars were constructed more strongly than passenger cars and a freight car 28 ft. long with a capacity of 9 ton, weighed 6 ton. In existing designs of open top cars the ratio of dead weight to pay load is approximately I to 3. The types of cars now in use on American railroads are developments from the early crude forms. Wooden freight cars are being rapidly replaced by all steel or steel underframe cars. Nearly all coal cars, either gondola or hopper, are now being made of steel. After Jan. 1, 1931, no wooden cars were accepted in interchange on American railroads. Early in this century the combination of pressed steel and structural steel was used in car construction and this is the type of construction most commonly used today. The 7o ton hopper cars have come into general use and also 90 ton, zoo ton and 120 ton capacity coal cars are in operation. The largest freight car in commercial use at present is the 120 ton capacity steel coal car. This is a type of gondola of which the most novel feature is its size.
A large number of "automobile" or box cars with large cubical capacity are in use in the United States. Many have end doors and all have wide side doors.
The number of freight train cars in service (1935) on railroads in the United States was as follows : (1) railroad owned or leased 1,596,711; (2) privately owned 295,664; total 1,892,375. Freight train cars installed in major steam railways during the year 1935 totalled 18,496, a very low figure due to the depression.
The average mileage made by a freight car in America is approximately 3o m. in 24 hours. The railroads of America are constantly speeding up train operation. It is predicted that in a few years freight trains will be operated at passenger train speeds. In America the percentage of empty to loaded car miles has run about 3o% during the past few years. Freight car heavy repairs become due in periods of about once every 8 or 10 years, whereas running repairs and inspections are a continuous necessity.