Development and Implementation of a Continuous Vertical Track-Support Testing Technique

Abstract

As part of an Association of American Railroads (AAR) research program, the Transportation Technology Center, Inc., a subsidiary of AAR, has developed a new method using its track loading vehicle (TLV) technique to measure vertical track deflections under given vertical loads while in motion. The technique was developed to identify weak track locations and to measure the load-carrying capacity of existing tracks to aid and prioritize track maintenance and to improve railroad operational performance. Discussed are the development and implementation of this continuous vertical track-support measurement technique. This technique provides an in-motion and nondestructive means of testing vertical track support. Currently, this newly developed TLV technique is being used in revenue service to identify large track stiffness variations along the track, indicating lower track strength or abrupt transitional stiffness changes. It is also used to locate the source of lower strength due to ballast and subgrade conditions, as well as to assess the need for upgrades to accommodate higher operation speeds or heavier axle loads. Extensive tests in revenue service have shown this TLV testing technique to be a viable method to perform the above tasks successfully. In addition, this new test technique can be used to improve the understanding of track strength degradation over time and to help direct limited maintenance resources to track locations requiring near-term maintenance.

Evaluating the potential of a rolling deflection measurement system to estimate track modulus

“…Over the past two decades, two deflection/track modulus measurement techniques have been developed and tested in North America: the Track Loading Vehicle (TLV) developed by the Transportation Technology Center, Inc. (TTCI) and the University of Nebraska Real-Time Vertical Track Deflection Measurement System (UNL system, commercially known as MRail) developed under the sponsorship of the Federal Railroad Administration (FRA). 6,13,[17][18][19] The focus of this study is on the UNL system that has shown the potential to measure deflection at relatively higher speeds and at lower equipment costs. 20 The UNL system measures the relative vertical distance (referred to as Y rel ) between the rail surface and the rail/wheel contact plane at a distance of 1.22 m from the nearest wheel to the sensor system.…”

“…The application of on-train techniques for measuring the track modulus at revenue speed provides a comprehensive overview of railway line conditions over long distances of track. 12–16 Despite this significant advantage, measuring the vertical rail deflection from a moving car is a challenge due to the difficulty in defining a reference point. Moreover, the interpretation of the on-train deflection measurement data still needs more investigation.…”

Estimation of vertical bending stress in rails using train-mounted vertical track deflection measurement systems

“…A number of train-mounted measurement systems have been developed for the estimation of track stiffness continuously along rails. 16–25 This includes the Track Loading Vehicle (TLV; developed by the Transportation Technology Center, Inc.) and the University of Nebraska Real-Time Vertical Track Deflection Measurement System (commercially known as MRail; developed under the sponsorship of the Federal Railroad Administration) that measure the VTD from moving railcars under axle loads that are representative of fully loaded railcars. 16,17,19,20 These train-mounted VTD measurement systems have potential use for the estimation of maximum bending moments and stresses in the rail by applying the mathematical correlation between rail deflections and bending stresses.…”

“…Train-mounted instruments that measure the vertical track deflection (VTD) under train loading have become available over the last decade. 16–20 These instruments present an opportunity to estimate rail bending stresses over long distances, and thus characterize the spatial variation of bending stresses. 15,16 However, the effect of track modulus and its variability on the mathematical correlation between rail deflection and bending stresses has not been thoroughly investigated and, as a result, the method used to estimate rail bending stresses from VTD measurements is overly simplistic.…”

Continuous Evaluation of Track Modulus from a Moving Railcar Using ANN-Based Techniques

“…Although these techniques provide accurate estimations of track stiffness, they are laborious and time-consuming, especially when multi-point measurements are required. On the other hand, on-train measurement systems allow the measurement of rail deflections over long distances and thus provide a good overall evaluation of the entire railway network [10][11][12][13][14][15]. Comprehensive analysis is typically needed to investigate the relationship between deflection measurements from on-train systems and track modulus [16,17].…”