Dynamic Effects of Track Surface Condition on Vertical Wheel/Rail Forces and Energy Consumption

Abstract

As track geometry degrades, and in particular as track surface and cross-level (as defined by a Track Quality Index or TQI) degrades, railway vehicles going over that degraded track experience increased vertical dynamic behavior and increased vehicle/track interaction. This in turn translates into increased wheel/rail dynamic forces as well as increased energy (fuel) consumption. While this concept has been known for many years, there has been limited study of the direct relationships between the degree of track degradation (as quantified by a Track Quality Index type parameter) and the magnitude of the dynamic force and energy consumption increase. This paper presents a recent study on the dynamic effects of track surface geometry degradation, which has direct impact on maintenance practices, policies, and economics. Specifically, this paper presents the results of a series of analyses looking at the effect of increased track geometry degradation, as measured by a track geometry inspection vehicle, and quantified by a Track Quality Index (TQI). The effects examined include loss of energy and wasted fuel due to dissipation of energy in the vehicle suspension, as well as the increase in dynamic vertical force at the wheel/rail interface. The analyses used over 100 miles of US main line (Class 1) railroad track geometry data for a broad range of track conditions (and corresponding Track and Surface Quality Indices); together with a sophisticated multi-degree of freedom vehicle dynamics model to develop a relationship between track condition and dynamic effects. The results are a series of non-linear relationships between track condition, as defined by TQI, and energy loss in the suspension system, i.e. energy dissipation. A second set of non-linear relations was also developed between track condition, as defined by TQI, and dynamic force multiplier, i.e. the ratio of dynamic force to static wheel/rail load. The paper presents these results in both mathematical and graphical form.