Is the changing distribution of transport modes the effect of supply-side factors or of competition? – The changing distribution of land freight transport modes can be explained with reference to two sets of factors : those having to do with changes in the production apparatus upstream of the transport market ; and those that affect the competitiveness of various modes on the transport market itself.On the first set of factors, changes in industrial organization affect distribution by changing the type of products transported. Using the traffic statistics by NST categories, the effect this phenomenon had over the period 1980-1991 can be measured in terms of shares of the market going to different transports modes. Changes in the freight structure “ explains” a sixth of the loss in market share by railroads, a third of that lost by inland waterways, and nearly a fifth of the gains recorded by road transport.----------------------------------------------With the author and the publisher of the copyright agreement. The present version in PDF is under the copyright of EDITECOM (http://www.editecom.com/) - 1993.Les changements qui sont intervenus dans la répartition modale du transport terrestre de marchandises au cours des 10 ou 15 dernières années sont bien connus. Cet article en rappelle les données essentielles en comparant les trafics de 1980 et de 1991. Ainsi, on constate le développement de la part de marché du mode de transport routier par rapport aux autres modes de transport. Des facteurs explicatifs sont apportés à ce constat par l'évolution de l'appareil de production des moyens de transports proprement dits, et, par des facteurs de compétitivité de chaque mode