TRAILER registration figures for the entire United States are given to show the rapid increase in the use of trailers in the last seven years, and, for comparison, State registrations of all motor-vehicles in 1931 are given.
To account for the relatively more rapid increase in trailers than in trucks, factors favoring the use of trailers are mentioned and illustrative examples of operation are briefly described. The factor of first importance is legislation, which in general is stated to have promoted the use of trailers to distribute the weight of heavy loads over more axles and wheels; but in some States the laws and regulations have a serious adverse effect.
Next to legislation, savings in hauling costs through the use of trailers account for the increase in their numbers, and comparative figures of the cost of hauling per 100 lb. per 100 miles by truck, by truck and trailer and by rail are given to show the economy.
Another important factor mentioned is convenience to shipper and consignee, and examples of the services rendered are cited. Operators are stated to foresee the development of a Nation-wide service with interchangeable trailers much as railroad freight-cars travel to all parts of the Country over various railroads. Before this can be realized, coupling mechanisms must be standardized so that any trailer can be coupled to any tractor. Difficulties that stand in the way of accomplishing this by a subcommittee of the Society are set forth.
Trailer designers have been confronted with a difficult task in designing the semi-trailer fifth-wheel coupling, which must satisfactorily meet a multitude of requirements, but they have succeeded in refining and reducing the weight of this mechanism and also of the trailer body.