Technology Digests / Truck Hunting Detector Evaluation: Repeatability and Reproducibility

TD24-010

September 10, 2024
Authors
  • Kenny Morrison
  • Walter Rosenberger
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Key Findings

  • The vast majority of trucks do not hunt, and the vast majority of THD readings are highly repeatable and reproducible with low HI values.
  • On the same truck with the same orientation, the same weight and speed, and a consistent direction basis, there is less than 0.05 variation in HI for:
    - 99 percent of truck passes over 
the same site.
    - 98 percent of truck passes over different sites.
  • Hunting is a performance attribute. Using THD measurements to identify trucks that are prone to hunting involves managing the exceptions. Most THD readings of HI ≥ 0.2 are statistical outliers and are not repeatable.
    - The analysis of THD data from individual trucks showed a slightly higher probability of repeating HI > 0.2 when passes within 120 days were at higher speeds and/or lighter truck weights.
    - For trucks generating at least one reading of HI ≥ 0.2, 38 percent of trucks with the same direction and orientation had an additional reading of 0.2 or greater within 120 days.

Truck Hunting Detector Evaluation: Repeatability and Reproducibility

Through the the Association of American Railroads’ (AAR) Strategic Research Initiatives (SRI) program, MxV Rail analyzed hunting detector data to understand measurements relative to true truck hunting behavior. The ultimate goal of performing the analysis was to provide the industry with greater confidence in the accuracy, repeatability, and reproducibility of hunting detection. Today’s truck hunting detectors (THDs) represent well over 20 years of research, development, testing, analysis, and experience. Work undertaken by Norfolk Southern (NS) and Salient Systems (now L.B. Foster Co.), with the help of the Federal Railroad Administration (FRA), corellated THD Hunting Index (HI) measurements with lateral carbody accelerations of vehicles known to hunt.1,2 Previous SRI work identified eight single-unit cars that performed poorly; five of the eight showed moderate to substantial improvement in hunting performance after repairs.3 Further SRI research found that multiple elevated HI measures were associated with specific mechanical deficiencies, such as wedge rise, roller…