Economies of Density versus Economies of Scale: Why Trunk and Local Service Airline Costs Differ

There has been a perception that U.S. trunk airlines had an inherent cost advantage over smaller regional airlines because of economies of scale. We have formulated a general model of airline costs, which we estimate by using panel data on large and small airlines. Differences in scale are shown to have no role in explaining higher costs for small airlines. The primary factor explaining cost differences is density of traffic within an airline's network. Also of major importance is the average length of individual flights.