Railways had been once the milestones towards modernization. Then road transport predominated over railway transport as a result of improved motorcars and high standard road networks. ― This conversion in transport has been found anywhere in the world. Focusing on Thailand as an example of modern nation-building by the construction of railways and highways, mechanisms of the conversion are studied with a quantitative analysis of commodity flow and the government’s transport policy. The Ohira-prize winner for the latest work sharply depicts the “declining” age of railways.