Substitute Goods.• The inclusion of a substitute travel price variable was tested on a subset of routes and was found to increase price elasticities. Estimates that exclude a meaningful substitute in the regression model will produce more inelastic estimates than a correctly specified model would produce. Route substitutes can be defined as a different airport serving the same catchment area (e.g. ChicagoO’Hare or Chicago-Midway) or a different destination serving the same purpose (e.g. Las Vegas or Reno)