Transportation Logistics CEE 498B/599I - PowerPoint PPT Presentation

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Transportation Logistics CEE 498B/599I

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  1. Transportation LogisticsCEE 498B/599I Professor Goodchild 4/18/07

  2. Routing and Scheduling • Which customers to be visited by each vehicle? • Sequence in which they will be visited • When will each customer be visited? • How much will this cost? • Minimize cost and travel time, missed deliveries, comply with constraints (truck size, driver hours)

  3. TSP and VRP • Traveling Salesman Problem (TSP): Given N points, find a tour that visits them all, returning to the point of departure, with minimum distance (here we are not dealing with many vehicles) • Vehicle Routing Problem (VRP): Find an allocation of points to vehicles, and a set of tours that return to a depot, that minimize either distance, number of vehicles, or a combination of the two (this is the same problem we addressed with the SMM and GA method, but number of vehicles not given)

  4. Text Example: Peapod • Online grocer • Each day has different realization of deliveries • Webvan • Example: • distance on grid proportional to actual distance traveled • Cost proportional to distance traveled • Capacity 200 units • Minimize distance traveled

  5. Location/Allocation • Segment the area (assign customers to a route) • Decide on route

  6. Sequence Customers on Routes • Determine an initial route (not necessarily optimal) • Farthest insert (add farthest from DC first) • Nearest insert (add closest to DC first) • Nearest neighbor (add closest to customer just added first) • Sweep

  7. Results are not always intuitive

  8. Route Improvement Procedures • Can we do better than original tours? • There are many ways you could do this: • 2OPT: break trip 2 spots, reconnect • 3OPT: break trip 3 spots, reconnect

  9. Transportation Networks • Direct Shipping • Milk-run • Distribution center (hub) • Tailored network (serving different customers with different modes, methods or frequencies)

  10. Trade-offs • Management complexity • Inbound/outbound transportation costs • Cost of facility • Inventory • Handling • Ability to respond to the customer • Mode

  11. In-class exercise • What attributes of a logistics system make milk-runs appropriate? (e.g. high density customers, large loads) • What attributes make a cross-docking facility appropriate? • When does it make sense to aggregate inventory?