Route Dummies.• These dummy variables were found in many cases to increase the explanatory power of the model, suggesting that some other route-specific factors are important for demand (e.g. whether or not non-stop service is available, whether there are competing carriers operating on non-stop routes,whether there is a low cost carrier, what types of cultural or financial linkages there are between pairs of cities). The use of route dummy variables controls for these variables without the need to quantify them