A long researched and very prevalent problem in several industry dealing with delivered products supply chain is VRP (vehicle route planning). Practitioners can add more to the list of complexity below, but you will get a good idea of the beast of a problem it is-

• Customers are spread across large area with significant distance and delivery lead times
• Some customer are order based and some you may be in service level agreement to manage minimum safety stock
• Vehicles in fleet may not match the delivery requirement (order or inventory replenishment)
• Company may have more than one supply locations to serve customers
• Vehicles are spread across network, some in-transit, some in maintenance, some available at supply locations
• Not all vehicles are Compatible with all sites (source/customer) for reasons like permits, vehicle size
• Enroute multi drop customer choices are numerous
• Customer and source and working time windows. For pickup and delivery if you miss it then the vehicle will be idling or there would be delays. In a multi drop trip hitting all the time windows right while choosing right customers in route.
• Customers have delivery sequence preferences or there may be physical limitations for un-economic route sequence.
• Source supply limitations or disruptions are commonplace
• Night driving restrictions, congestions and weather disruptions will trigger need rescheduling
• Changing one vehicle trip assignment has cascading impact on other customers, supply side product availability, costs etc.
• Coupled with all this driver availability, labour laws makes the problem extremely complex