I have large number of flow items coming to the model based on an arrival schedule. these items are going to be transported from/to two objects on specific transporters. E.g. item type 1 only goes with transporter 1, item type 20 only goes with transporter 20... . On each trip, there might be 1, 2, 3 or more flow items loaded on to the transporter and the transporter should not leave before all of assigned items are arrived and ready to go. The flow item types come in series. (E.g. arrival 1, arrival 2, and arrival 3 are item type 1, arrival 4, and arrival 5 are item type 2, ...). How can I make the transporters wait for the right flow items to arrive and load them and the leave? I would appreciate any comments or references that might can help.