THE SAFETY IMPACT OF WAGON HEALTH MONITORING IN NORTH AMERICA

North American railroads and car owners are using a new process of condition-based freight car maintenance strategies designed to ensure that adverse vehicle conditions are identified and rectified. Current wayside detector systems implemented by North American railroads include wheel impact load detectors (WILD), hunting detectors, truck performance detectors (TPD), hot and cold wheel detectors, acoustic bearing detector systems (ABD), wheel profile measurement systems, brake condition monitoring systems, and cracked wheel detection systems. The Association of American Railroads (AAR) Advanced Technology Safety Initiative (ATSI) is an effort to make the overall freight interchange system safer and more efficient by taking advantage of new technologies that facilitate more sophisticated assessment of the condition of in-service equipment. This approach can both enhance the performance of rail equipment and prolong the life of railroad infrastructure. AAR and Transportation Technology Center, Inc. (TTCI) have estimated the effect of ATSI on broken wheel and broken rail accidents, and on bearing-related accidents for Class I railroads on mainline track. The Federal Railroad Administration’s (FRA) safety database was analyzed for these cause codes both before and after implementation of ATSI in October 2004. The results of the statistical analysis indicate that there are substantial safety benefits associated with wayside detector implementation, with the primary benefit being improved safety. Since the beginning of the ATSI program in 2004, the North American railway industry has realized reductions in broken rail and broken wheel derailments, and bearing-caused and car-hunting-related derailments. This paper describes the current wagon health monitoring technologies, the current implementation of a new process of conditioned-based freight car maintenance strategies designed to ensure that adverse vehicle conditions are identified and rectified. It additionally presents results from a post audit conducted by an outside consulting firm to quantify the economic benefits of various wayside detectors deployed by the North American railways. The post audit conducted by the independent consultant showed that the net benefit of wayside detectors is estimated to be $226.7 million through 2008. Research costs from 1990 to 2008 are approximately 4.782 million, representing a return on investment of 47 times its total cost. INTRODUCTION As many railways around the globe migrate from government-run institutions to private concessions, there may be some lessons that can be learned from North American experiences. With increasing axle loads and annual tonnage on mainline tracks, there is a continuing need to implement technology to control the stress-state at the wheel/rail interface. The historic trend in the North American railroad industry has been to meet the demands of heavier axle loads by increasing the strength of the track structure. This method requires extensive capital expenditures and does not always produce the desired results. With recent privatizations in Canada and Mexico, the railroads of North America now operate almost exclusively on privately maintained rights-of-way. Unlike other competing transportation modes, they are fully responsible for right-of-way maintenance and restoration. They operate on about 230,000 kilometers of route and own 786,000 freight cars and more than 24,000 locomotives. In addition to the freight cars North American railroads own, they haul about 819,000 additional cars owned by private car companies, lessors, and shippers or consignees. In the United States alone, privately owned cars actually outnumber railroad owned cars by 776,000 to 617,000. Despite ownership, most railcars move seamlessly from one railroad to another toward their destination. (A few special cars move by agreement between the car owner and operating railroads, but these are the exception.) One of the primary functions of the AAR is to provide an industry-wide means of satisfying mechanical requirements for efficient interchange of freight cars. Challenge H: For an even safer and more secure railway 2 Some of the maintenance strategy changes described in this paper will most likely rely on car owners taking proactive steps to correct problems before they reach levels where they adversely affect the stress state of the railroad and the rail vehicle as well. This effort is led by the ATSI Task Force appointed by the AAR’s Safety and Operations Committee. The latter committee is made up of the chief operating officers of North America’s largest railroads. Much of what is described here is a “work in process” and changes are incorporated as the newly revised processes evolve. TRACKSIDE WAGON HEALTH MONITORING SYSTEMS As new technologies come on line, the number and types of detectors with Internet data access capability have grown rapidly in North America. At last count, the North American railroads have 136 WILDs, 25 TPDs, 7 wheel profile measurement systems (WPM), and 13 ABDs. More of each type of detector system is on order or in capital plans. Machine vision and other available or emerging technologies are being actively developed by TTCI, USA, in partnership with suppliers worldwide and are expected to be on line within the next few years. Traditionally, detectors systems are set to alarm when preset criteria are exceeded. Most systems control signal aspects or are “talkers,” which communicate with the train crew by radio using a synthesized voice noting any exception detected and the axle count from the lead locomotive axle to the indicated defect. Most wayside detectors are in an advanced stage of implementation throughout North America. The following is a description of the function and the use of some of the existing detectors in N. America. Wheel impact load detectors, shown in Figure 1, measure vertical wheel loads as the car passes across the site. Their primary function is to measure vertical impact loads to identify out-of-round wheels for removal beyond a specific level. Many have subsequently been adapted to function as overload and imbalanced load detectors (OILD), as well as truck (bogie) hunting detectors (THD) The function of OILDs is self explanatory. THD utilize an algorithm based on the yawing motion of the wheelsets of the bogie relative to the track to identify poorly performing bogies and, in particular, 3-piece bogies with poor truck warp (lozenge) stiffness and/or low bogie rotational resistance to the body. Truck performance detectors (TPD) have been deployed to monitor the tracking performance of vehicles, particularly on curved track. These detectors use either strain gages to measure vertical and lateral forces or laser position sensors to measure the lateral and yaw attitude of the wheelset (Figure 1). These detectors identify:  Radially misaligned wheels occurring on 3-piece North American bogies when two side frames in the same truck have mismatched wheelbases  Low bogie warp (shear) restraint from missing main or wedge springs, worn wedges, loose or worn column wear liners  Mismatched wheel diameters on the same axle, either as a result of poor machining or as a result of eccentric profile wear between wheels on the same axle Wheel temperature measuring devices (WTMD) use similar technology to hot box detectors (HBD) to identify unbraked wheels when they should be braking and unreleased brakes when the wheels should be running freely. Algorithms are developed to cater for a specific wheel’s temperature in relation to all wheels in the train. Unreleased handbrakes, inoperative or malfunctioning valves, and binding brake rigging are identified. Wheel profile measurement systems measure the complete profile, identify traditional metrics (e.g., flange thickness, height, and rim thickness) and introduce new and additional useful metrics associated with the asymmetry of the wear on the wheel. The Acoustic Bearing Detectors (ABD) are state-of-the-art in bearing defect detection systems (Figure 2). For many years railroads have relied on either HBDs or scheduled maintenance to prevent overheated bearings. The acoustic bearing detector allows railroad operators to detect defects long before they cause overheating and plan bearing maintenance based on performance. The ABD allows railroad operators to detect defects long before they cause overheating and to plan Challenge H: For an even safer and more secure railway 3 bearing maintenance based on performance. The minimization of service disruption is a major economic driver of an ABD as well as the prevention of catastrophic failures that can occur despite a network of HBDs. Due to the early warning capability of an ABD, a large number is not required provided that individual bearings are monitored over a reasonable time or mileage interval. Figure 1. The North American railway industry’s existing array of wheel impact load and truck performance detectors provided the opportunity for rapid implementation of new rules for identification and removal of high-impact wheels and poorly performing trucks. Figure 2. (l) TADS® installed on Union Pacific Railroad and (r) a photo of a defective bearing found by the system. Recently TTCI partnered with DAPCO, a Connecticut-based ultrasonic inspection company, to develop a detection system capable of inspecting internal wheel defects such as shattered rims and wheel tread defects. The prototype system, which was subsequently installed at TTC, is capable of inspecting one side of a railcar at speeds up to 8 kph (5 mph). The design included servo-driven, tandem inspection heads guided by a rack-and-pinion system capable of tracking car wheels at speeds of 2.4 meters per second (8 feet per second). The inspection system is comprised of four stations, each with the probes and tracking systems to measure all four wheels of one side of a freight car. Figure 3 shows a production system installed at Union