Dr. Nii Attoh-Okine and Emmanuel Martey (graduate student), University of Delaware
Assessing and maintaining track geometry within acceptable limits are key components of railroad infrastructure maintenance operations. Track geometry conditions have a significant influence on rider comfort and safety. To maintain the ride quality and safety of the track, maintenance activities pertaining to track geometry, such as tamping, are performed. Tamping enhances the track geometry quality but fails to return the track geometry to an as-good-as-new condition. Majority of studies have evaluated tamping recovery using deterministic techniques, which assume that tamping recovery is dependent on the track geometry quality prior to tamping. However, they fail to capture the uncertainty of the recovery values. Probabilistic approaches are increasingly being used to account for the uncertainty but fail to model the underlying dependence between the variables, which may exhibit nonlinear dependencies such as tail or asymmetric dependence. To accurately model the tamping recovery phenomenon, this research conducted by University of Delaware employs the copula models in combining arbitrary marginal distributions to form a joint multivariate distribution with the underlying dependence. Copula models are used to estimate the tamping recovery of track geometry parameters such as surface (longitudinal level), alignment, cross level, gage, and warp.
The results of this study showed that the after tamping recovery (correction) of the track does not behave like a traditional two-parameter normal distribution but rather has a distinct distribution (a three-parameter log-normal distribution) which can be used to better predict the results of the track tamping operations. Similarly, non-normal, behavior was also observed for the track quality condition before and after tamping.
Implementation of Research Outcomes
The results are part of an integrated activity looking at improving tamping performance and improving overall track maintenance effectiveness. This is one part of a multi-pronged activity.
Impacts/Benefits of Implementation
The results of this activity can be used to improve the quality of track maintenance by providing better guidance on how to improve the effectiveness of the track tamping operation. This in turn leads to a better track condition, improved ride quality, and reduced overall maintenance cost. In addition, the results can help develop improved track maintenance scheduling models by providing a better understanding of the quality of the track, its overall condition, after tamping maintenance. This will result in improved maintenance efficiency and reduced maintenance costs. Finally, by better understanding the tamping recovery phenomena more effective maintenance management models can be developed that will result in better and more durable track conditions, with corresponding improvements in ride quality and safety.
These results have been published but have not yet been incorporated into a maintenance management model.
E. Martey and N. Attoh-Okine, Modeling tamping recovery of track geometry using the copula-based approach, Journal of Rail and Rapid Transit, Volume: 232 issue: 8, page(s): 2079-2096, https://doi.org/10.1177/0954409718757556