But once the fleet is determined, most XM car selections should be based on a mathematically random chance, subject to some individual cases of 'skew' for specially equipped or assigned cars.
And I forgot to add, for Mike Brock, that waybill assignments do NOT determine train composition. Once the destinations for the cars have been chosen more or less randomly, then the logic of train operations takes over, and has a significant effect on the makeup of individual trains.
