Understanding the Benefits of Long Travel Constant Contact Side Bearings

In 2001, a comprehensive test program was conducted under the AAR strategic research initiatives program by the Transportation Technology Center, Inc. (TTCI), Pueblo, Colorado, to determine the best types of constant contact side bearings (CCSBs) for use in 10 different North American freight cars. Test results indicated that long travel (LT) CCSB designs generally provided the best overall performance, which lead to an industry wide rule change. By using LT-CCSB, rail operations can be improved by maintaining better vertical wheel loads, providing high-speed stability, and providing more predictable truck turning forces. With a better understanding of both CCSB performance and the needs of the rail industry, an updated specification M-948 (AAR’s Manual of Standards and Recommended Practices) [Ref. 1] was researched and revised in 2005. This paper documents the evolution of LT-CCSB research and the industry’s implementation efforts since testing began in 2001. The testing and modeling that was performed in 2001 concentrated on car types that had a history of unpredictable performance. Well-maintained cars were selected to highlight the characteristics of long, short, tall, and torsional stiffness that each plays a part in the vehicles ability to reliably negotiate the railroad. Of the 10 cars, four were both track tested and modeled and the balance were only modeled. In almost every case, the railcars had a demonstrable performance improvement with the simple application of LT-CCSBs. The AAR quickly reacted by requiring all new cars and cars meeting certain conditions to have LT-CCSB (Rule 88) [Ref. 2]. Following this test program two other independent tests were conducted, which demonstrated the advantages of LT-CCSBs. The first was a rail service test of two diesel tank cars and the second was a series of controlled tests on a tank car that had derailed at high speed. In both cases performance was markedly improved by the application of LT-CCSB. Finally the industry needed to update the side bearing specification M-948, in order to reliably control the performance of LT-CCSBs and preserve the benefit derived from their use. In preparation, a 2-year rail service test was conducted on three different cars, which were a refrigerated orange juice boxcar (operated in high speed intermodal or “Z-train” service), an intermodal car, and a coal gondola. Using the data from these cars and knowledge from participants in the CCSB supply industry, the M-948 specification was revised to represent and preserve the operational benefits derived from CCSBs. This paper will also document an audit of the specification to highlight advantages from the revised M-948 specification.