City sizes and transport costs[Tailles de villes et coûts de transport]

In this paper, the conjecture that city size doesn't lead to economies of scale in operation of urban public transportation is successfully tested with data over 47 French towns. Operating costs are increasing stronger than city size. This is due to a larger supply per inhabitant and to bigger unit cost (per seat kilometre). The urban area of Paris is an exception to the rule of the increasing unit cost, but because of the important service level, operating costs per inhabitant are nevertheless higher than those of smaller cities. The comparison between Paris and the provinces puts forward that the capacity of bus and trains could be very important for improvement in productivity. However, vehicles capacity increasing seems to be significant only in huge urban area, as Paris for instance. But those diminishing operating costs could be balanced by travel length and travel time. In this respect, it is worthy to mention the possible gap between the productivity of urban services and the efficiency of an urban area considered as a whole.