Technology Digests / Deterministic Hunting Risks Based on Car Characteristics

TD22-005

May 1, 2022
Authors
  • Kenny Morrison
  • Walter Rosenberger
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Key Findings

  • The deterministic hunting risk methodology developed to assess typical speed restricted equipment can also evaluate car types and physical characteristics.
  • The various car characteristics studied had substantial differences in hunting risk rates.
  • Many characteristics, such as length, had hunting risk rates that corroborated and quantified historical experience.
  • The risk rates for some characteristics were counter to experience. For example, long travel CCSBs had higher rates than short travel CCSBs at speeds 60 mph and above.
  • Because the various car characteristics overlap on the populations of equipment, care must be used when selecting equipment groups to evaluate hunting risk rates.

Deterministic Hunting Risks Based on Car Characteristics

As part of the Association of American Railroads’ (AAR) Car and Truck Systems Strategic Research Initiative program, MxV Rail (formerly TTCI) was asked to study the conditions related to high-speed instability, better known as “hunting.” This effort continues the work described in a previous Technology Digest 1 to optimize hunting speed restrictions. This work shows how the hunting risk methodology can assess various car characteristics. Six fields from the UMLER® registry were selected for evaluation: 1) constant-contact side bearing (CCSB) type, 2) truck center length, 3) outside length, 4) tare weight, 5) equipment type code, and 6) outside extreme height. The results of this study appear to show differences in hunting risk levels of the populations as defined by these car characteristics. However, the characteristics may be related, such that their effects on hunting were not isolated. As a result, some of the outcomes appear to be counter-intuitive. For example,…