1. A computer-implemented method for generating a schedule for a network of transportation resources, the method comprising: selecting a plurality of market pairs in a transportation network; identifying a quantity of flights to be flown over at least a marketing day for each market pair, wherein the quantity of flights includes more than one flight; determining a range of permissible departure times or arrival times for each market pair in the selected plurality of market pairs; iteratively generating, by operation of at least one computer, sets of variables for each market pair using an objective function and based on at least the determined range of permissible departure times or arrival times for the market pair and spacing parameters, wherein each generated variable represents a different set of possible departure times or arrival times for adjacent flights associated with a particular market pair, each different set including a possible departure time or arrival time for each flight in the identified quantity of flights for the particular market pair, and each different set is generated in accordance with the spacing parameters that define spacing between adjacent departing flights or adjacent arriving flights associated with the particular market pair; and building, by operation of at least one computer, a proposed schedule based on the generated sets of variables for each market pair and a set of constraints by selecting a variable of the generated sets of variables, wherein the selected variable represents a selected set of departure times and arrival times for a plurality of flights associated with the market pair, and the set of constraints includes at least one constraint selected from a group consisting of a number of transportation resources, services to be provided by transportation resources, a number of segments to be served by transportation resources between each of a plurality of locations, and constraints on sequential associations of segments.