Proceedings of the 2015 Industrial and Systems Engineering Research Conference S. Cetinkaya and J. K. Ryan, eds. A Bi-objective Railroad Track Inspection Planning Problem Hadi Farhangi, Dinçer Konur, Suzanna Long, Ruwen Qin Missouri University of Science and Technology, Rolla, MO, USA Jennifer Harper Missouri Department of Transportation, Jefferson City, MO, USA Abstract Track inspection, specifically automated ultrasonic inspections of railroad tracks, is one of the most important safety operations that State Department of Transportation and railroad companies need to plan. This study analyzes a track inspection scheduling problem (TISP) considering the practical constraints and objectives of track inspections. TISP is a bi-objective binary optimization problem, where the total time to complete the predetermined number of inspections on a given set of railroad tracks is minimized and the total weighted importance of the inspections is maximized. We explicitly consider the track inspection times, the travel times between tracks, and the time required between two consecutive inspections of the same track. Two greedy algorithms are proposed and used to approximate a set of Pareto efficient inspection schedules. Keywords Track inspection, Bi-objective, Optimization, Greedy Algorithm 1. Introduction and Literature Review Track failures are among the major problems that railroad companies frequently face [16]. These companies make substantial investments to maintain the serviceability of their tracks. Similarly, State Departments of Transportation need to maintain safety of the public railroad network. The first step to keep tracks safe and serviceable is track inspection, which is usually followed by track maintenance activities [18]. In the literature, track inspection planning and maintenance planning are treated as different problems. Unlike track maintenance planning, which has been broadly studied by operational research techniques [3, 7, 10, 15, 19], track inspection planning has not been widely investigated with operations research tools [16, 18]. Particularly, track maintenance planning studies focus on the scheduling of maintenance activities on tracks, where a specific maintenance is required. These studies formulate and analyze optimization models for planning maintenance operations to minimize the total traffic delay on the railroad network due to maintenance activities [10] and/or minimize costs related to maintenance activities such as crew costs, travel costs [7, 20]. Nevertheless, track inspection scheduling has different settings than maintenance planning/scheduling problems. In maintenance planning, it is known which maintenance operations should be completed on which tracks. On the other hand, in track inspection scheduling, all of the tracks of the given railroad network should be inspected regularly. It should be noted that some tracks should be inspected more frequently than the others as they might have higher potential for failure due to high traffic or they might have higher safety requirements due to the type of traffic such as hazardous materials traffic or public transportation. Furthermore, in track inspection planning, one should consider that the next inspection of a track should be after a specific time period in order to estimate failures accurately. For instance, in two months, if a track is inspected 4 times within the same week, these inspections would indicate similar observations and would ignore possible failure implications in the remainder of the this two months period. In this study, we account for these practical settings of track inspection scheduling. It should be noted that there are several aspects of track inspection that are discussed in the literature such as soil inspection, bridge inspection, railhead inspection, bottom edge inspection, track gauge inspection, and crane inspection [2, 5, 6, 9, 11, 17, 21, 22]. As noted by Missouri Department of Transportation, sponsor of this research, the focus of this study is set on scheduling a track inspection vehicle for ultrasonic inspections, we, therefore, consider the travel time of the inspection vehicle from one track to another. We use operations research techniques for analyzing the