indicators that characterize the freight volume by direction and sections of a transportation network, as well as among corresponding enterprises, points, or regions. Freight flows may be depicted by graphs or diagrams or in the form of so-called oblique tables, in which corresponding points and the freight volume between them are represented. As a rule, freight flows over individual sections of a network and in the “outbound” and “return” directions are not equal.
Within the USSR the largest freight flows occur on routes that connect the main mining, metallurgical, and lumber industry regions with the large processing-industry centers (for example, the Donbas and the Central Zone, the Kuznetsk Basin with the Urals). The direction of predominant freight flow (for example, from the Donbas to the Central Zone) is called the loaded direction, and the return direction is called the empty direction. In the USSR the amount of cargo shipped in the empty direction is about three-fifths of that shipped in the loaded direction. The inequality of freight flows along the outbound and return routes results in empty trips for rolling stock, unproductive trips by locomotives, ships, and motor vehicles, and an increase in the prime cost of shipping and capital outlays. Measures are being implemented to increase the freight volume sent in empty directions in order to moderate the inequality in freight flows; these include the use of reduced tariffs.
The size of freight flows is measured by the density of freight traffic. It depends on the production volume, the freight turnover associated with the volume, and the extent of the network. The average freight density on the railroads of the USSR is 18.5 million ton-kilometers per kilometer, which is three times higher than the average world freight density and five times that of the USA. A higher degree of use of transportation production capital and low prime cost generally accompany a high freight-traffic density. However, the task of providing continuous transportation operations and its maintenance is becoming a complex undertaking. Thus, because of the excessively high freight traffic densities on some transport routes, parallel routes are being constructed.