It just dawned on me that an inexpensive little application I bought for work might have use in model operations. It is a random number generator. You can select a range where the numbers will fall (1 through your total number of cars, say 20, 200 2000?); the total number of numbers you want generated (your maximum train size for example), and select that there be no duplicates. It has a feature to export to Excel and from there it could go just about anywhere. Hmmm. Anyone used such a thing to determine car movements, etc? It cost me $15 for the download a few years back. I'm not on my work pc right now so I don't have the name but I bet you could google it quite easily. ???