Reliable service systems design under the risk of network access failures

In service systems with natural or anthropogenic barriers (e.g., rivers, railroads), customers who intend to visit facilities for service must first pass through certain network access points (e.g., bridges, railway crossings). Possible blockage or disruptions of these access points could change the customer-facility assignments or even affect reachability of various facilities, and thus introduce facility reliability and correlation issues. This paper incorporates network access points and their probabilistic failures into a joint optimization framework. A layer of network access points are added and connected to facilities to imply the real-world connections between facilities and access points. The access points are assumed to be subject to disruptions with site-dependent probabilities. We then develop a compact mixed-integer mathematical model to optimize the facility location and customer assignment decisions for the service systems design. Lagrangian relaxation based algorithms are designed to effectively solve the proposed model. Multiple case studies are constructed to test the model and the algorithm, and to demonstrate their performance and applicability.