EVERAL generations of Americans and Canadians have first become acquainted with the economic geography of their countries at the railroad crossing. A typical freight train, composed of 100 cars which may be owned by 30 different railroad companies, presents a pageant of the economic interconnections that bind together the various regions of the United States and Canada. But the uniqueness of this familiar feature of the North American landscape is not commonly realized. With the grouping and subsequent unification of British railways into a single national system, the railroads of Anglo-America were left alone in their specialized functions. Because the American-Canadian railnet is composed of hundreds of separate companies, only rarely do shipments originate, travel, and terminate on the lines of a single railroad. Most freight is loaded on the lines of one railroad and unloaded on another. On only 15 major railroads does tonnage originated and terminated on-line predominate, and only two major systems, both in Canada, have traffic that is composed more than half of internal or local' shipments. The two exceptional systems are the Canadian National Railways and the Canadian Pacific Railway, each of which has lines serving nearly all parts of Canada. These two large Canadian systems are the closest Anglo-American approximation to the unified national rail systems prevalent in most of the world. Most Canadian and American railroads are specialized in some phase of freight haulage, that is, originating, terminating, or carrying traffic between other systems-the bridge line function. Elsewhere in the world, the organization of the railnet into unified national or regional systems, either at the outset by state construction or later by governmental acquisition, has caused most rail systems to function primarily as discrete units. In the few places where separate rail systems do exist, the characteristic lack of connection or significant traffic interchange among systems preserves discreteness, and the vigorous flow of freight between separate railroads and consequent specialization of function that is characteristic in Anglo-America does not take place. The importance of traffic interchange and its effect upon the functions of Amer-