Vehicle routing problem with soft time windows and a case study

VEHICLE ROUTING PROBLEM WITH SOFT TIME WINDOWSAND A CASE STUDY(M.Sc. Thesis)Emrah AYDEM RGAZ UNIVERSITYINSTITUTE OF SCIENCE AND TECHNOLOGYSeptember 2006ABSTRACTThe cost of routing vehicles represents an important component ofmany transportation and distribution costs in a logistics system. Thetypical vehicle routing problem involves in designing a set of minimum-cost routes for a fleet of vehicle. Each route originates and terminatesat a single depot and serves a set of customer with known demands.The vehicle routing problem with time windows is a generalization ofthe vehicle routing problem where the service of a customer can beginwithin the time window defined by the earliest and the latest times whenthe customer will permit the start of service. The vehicle routingproblem with soft time windows (VRPSTW) is a variation of vehiclerouting problem with time windows in which time windows can beviolated by paying appropriate penalties.In this study an automotive factory which has 42 suppliers andimplements just in time system has been considered and its routingproblem with suppliers has been sold as VRPSTW and the optimalsolution has been provided. Goals of the case study are minimizingtotal operational cost, satisfying time window preferences of suppliersand avoid underutilization of vehicles capacity.For solving the problem first phase enumerates all feasible rotes. Thento find best routes enumeration-followed-by-optimization approach hasbeen represented and this approach has been implemented to casestudy. For enumerating feasible routes and for filtering them aprogramme has been coded with Visual Basic 6.0 and the feasibleroutes are solved by Lingo 8.0, optimization software, to get the optimalsolution.This methodology is recommended for solving real-life medium-sizedproblems. It provides optimal solutions in a acceptable computationaltime.Automotive factory?s existing routes and the optimal routes arecompared and at a ratio of % 13, 2 improvement has been provided.