Interface - The Journal of Wheel/Rail Interaction

WAYSIDE DETECTION SYSTEMS

Wayside Detection Systems Move to the Forefront of the Stress State Landscape (continued)

High-Speed Lateral Stability

Norfolk Southern has used an array of truck performance detectors in order to identify and quantify the effects of hunting—a phenomenon that has been shown to wear friction components in trucks and contribute to track degradation. Truck hunting is directly related to the high-speed lateral stability of a railway vehicle. Parameters such as vehicle speed, track conditions and friction levels affect whether a typical three-piece truck will hunt.

"Worn trucks are more likely to hunt, particularly at higher speeds," said L. Scott Keegan, senior engineer, at NS Research & Test. "Empty cars are more prone to hunting than loaded cars."

While truck hunting is not a major cause of derailments, hunting-related derailments do occur. More commonly, the violent carbody oscillations associated with hunting wear friction components in the truck and cause lading damage. And while it's difficult to assign a hard cost to it, hunting contributes to track degradation.

Working under the sponsorship of the FRA Office of Research and Development, NS established a car performance monitoring station on a 50-mph, 80-mgt line at Flat Rock, Kentucky. NS installed a Salient Systems WILD system, Wayside Inspection Devices' Truck/Bogie Optical Geometry Inspection (T/BOGI) laser/camera-based system, and a proof-of-concept system from Lynxrail and the TTCI, which uses wheel proximity sensors to identify hunting motions. “By using three, rather than a single reading system, we can clearly identify wheelsets that are oscillating, or hunting, as they move down the track,” Keegan said.

NS mounted lateral accelerometers on a consist of the worst of the bad actor covered hoppers, coal cars and autoracks identified by the WILD and T/BOGIE systems. The consist was operated at speeds ranging from 20 to 50 mph across the detector site, with data fed directly to a research car that was part of the consist. There was strong correlation between the wayside detectors, which record truck motion, and the onboard sensors, which characterize carbody motion. There was also strong correlation of the data on individual trucks among the three wayside systems.

Through these tests NS found that while hunting tends to increase with speed, particularly within the 35- to 50-mph range, there are periods during which vehicles that have become excited may dampen back down. Worn trucks are more likely to hunt than new or well-maintained trucks. Friction conditions also play a role.

While this work has been a Research and Test function, NS has developed a stress-state focus group, in which the Transportation, Mechanical, Engineering, and Signals and Communications Departments all have input into what the detectors are monitoring and how future installations may help improve safety and maintenance strategies.

"As we move forward, we need to bring in other segments of the industry, including private car owners, to develop standards and acceptance procedures that are satisfactory to all stakeholders in the railroad industry," Keegan said.

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