LAST STOP
Freight rail research and implementation: Answering challenges and pulling us forward By Gary Fry, Ph.D., P.E., Vice President, Fry Technical Services, Inc.
S
cience smiles approvingly at the sight of hard steel wheels rolling along hard steel rails and at the favorable aerodynamics of a train’s slipstream. So much so that rail transportation is a globally compelling resource to develop and maintain. On every continent, except Antarctica, railways are critical lifeline infrastructure systems. Regarding freight train efficiency, the heavier and the longer, the better. There are no theoretical limits as to the maximum weight or maximum length of a freight train. But there are certainly practical challenges that arise from economic, social, political, technological, geographic, geologic, and topographic conditions, all of which must be answered successfully. Often it is through research and implementation that effective answers are found. For example, prior to around 1970, a normal heavy axle load in North America was 25 tons. By the year 2000, 36-ton axle loads were approved for interchange service in North America and became widespread in use—an increase of more than 40%. This substantial shift in the definition of maximum allowable axle loads did not come easily. Among other challenges, as implementation of axle load increases progressed in revenue service, a major engineering hurdle was encountered in the form of metal fatigue. Metal fatigue is the formation of cracks in otherwise sound metal after the accumulation of many load cycles. These fatigue cracks can lead to complete fractures of the components that contain them, but oftentimes it was only after accumulating on the order of millions of load cycles. In simple terms, for the pearlitic steel alloys used in the rail industry, fatigue damage accumulates with load intensity raised roughly to the third power. That means if nothing changes except increasing axle loads by 40%, a factor of 1.4, the fatigue damage per load cycle could be nearly three times more severe: 1.4 x 1.4 x 1.4 = 2.7. Stated another way, the expected safe service life of the components would decrease by 2.7 times. An overview of techniques to model this phenomenon is provided in Fry and Tangtragulwong (2018). In response to the situation on the ground, comprehensive, coordinated, multinational research efforts were undertaken. The common
36 Railway Track & Structures // April 2022
objectives were to develop new knowledge, new materials, new designs, new technology, and new recommended procedures that would support safe and economical operations under heavier axle loads. Within 10 years, work accomplished by the many research and development teams representing industry, government, and academia began to have a measurable and positive impact. Guided by the research results, suppliers around the world developed improved rail steel, improved rail welding materials and procedures, new alloys for special trackwork castings, new wheel alloys and wheel plate designs, new axle designs, new bearing alloys and designs, new designs for bogie systems, new railcars, and more. Of equal and critical significance, the railway companies were able to make the necessary investments to implement the new technology. It is perhaps most illustrative to view the outcomes of this remarkable global endeavor from a safety point of view. Figure 1 is a graph displaying total derailments (including events on mainline, yard, and siding tracks) per million train-miles in the U.S. from 1975 to 2020 (FRA 2021). Red markers indicate the impact of a future safety challenge goal of eliminating all mainline derailments by the
year 2030. In the U.S., between 1975 and 2000 maximum allowed axle loads increased by 40% (from 25 tons to 36 tons), and the derailment rate per million train-miles decreased by over 70%. There also were economic gains associated with implementing heavier axle loads. For example, Martland (2013) estimated that the widespread implementation of 36-ton axle loads in the U.S. between 1994 and 2010 resulted in net cumulative benefits of over $5 billion USD. Compared to not increasing axle loads, and not utilizing the enhanced materials and technology, these benefits continue annually even today. The years 1970 to 2000 were remarkable in terms of the challenges undertaken and answered by the global heavy-haul freight rail transportation industry and its research partners. Though a specific and focused desire to further increase axle loads does not exist into the foreseeable future, many opportunities and challenges remain that offer potential to enhance the safety, efficiency, and efficacy of heavy-haul freight rail transportation. Creative attention, time, and support for research and implementation are still essential as we look to the future of freight rail transportation.
Figure 2. Total derailments in the U.S. per million train miles (FRA 2021). rtands.com