A model enhancement approach for optimizing the integrated shift scheduling and vehicle routing problem in waste collection

This paper presents a model enhancement approach for the integrated problem of developing shift schedules and waste collection routes. Given a variable amount of waste to be collected the objective is to find fixed, minimal cost shift schedules and collection routes under a service level constraint. While regular shifts during traffic peak hours are cheaper in terms of labour costs, the collection speed is on average lower than during expensive, non-regular shifts. Our findings can be summarized as follows. (1) Solutions can be found within reasonable computation time for real-life instances. (2) The model enhancement approach accurately estimates the required collection times and therefore consistently finds a feasible solution. (3) The solutions not only result in considerable savings, but are also proven to be (near)optimal by comparison with a practical lower bound based on flexible routes.