Vehicle Track Interaction Safety Standards
Authors: Marquis Brian , LeBlanc Jon , Tajaddini Ali 
Published: June 2014

Vehicle/Track Interaction (VTI) Safety Standards aim to reduce the risk of derailments and other accidents attributable to the dynamic interaction between moving vehicles and the track over which they operate. On March 13, 2013, the Federal Railroad Administration (FRA) published a final rule titled “Vehicle/Track Interaction Safety Standards; High-Speed and High Cant Deficiency Operations” which amended the Track Safety Standards (49 CFR Part213) and the Passenger Equipment Safety Standards (49 CFR Part 238) in order to promote VTI safety under a variety of conditions at speeds up to 220 mph. Among its main accomplishments, the final rule revises standards for track geometry and enhances qualification procedures for demonstrating vehicle trackworthiness to take advantage of computer modeling.

The Track Safety Standards provide safety limits for maximum allowable track geometry variations for all nine FRA Track Classes — i.e., safety “minimums.” These limits serve to identify conditions that require immediate attention because they may pose or create a potential safety hazard. While these conditions are generally infrequent, they define the worst conditions that can exist before a vehicle is required to slow down. To promote the safe interaction of rail vehicles with the track over which they operate (i.e. wheels stay on track, and vehicle dynamics do not overload the track structure, vehicle itself, or cause injury to passengers), these conditions must be considered in the design of suspension systems. In particular, rail vehicle suspensions must be designed to control the dynamic response such that wheel/rail forces and vehicle accelerations remain within prescribed thresholds (VTI safety limits) when traversing these more demanding track geometry conditions at all allowable speeds associated with at particular track class.

To help understand the differences in performance requirements (design constraints) being placed on the design of passenger equipment suspensions throughout the world, comparisons have been made between FRA safety standards and similar standards used internationally (Europe, Japan, and China) in terms of both allowable track geometry deviations and the criteria that define acceptable vehicle performance (VTI safety limits). While the various factors that have influenced the development of each of the standards are not readily available or fully understood at this time (e.g., economic considerations, provide safety for unique operating conditions, promote interoperability by providing a railway infrastructure that supports a wide variety of rail vehicle types, etc.), this comparative study helps to explain in part why, in certain circumstances, equipment that has been designed for operation in other parts of the world has performed poorly, and in some cases had derailment problems when imported to the U.S. Furthermore, for specific equipment that is not specifically designed for operation in the U.S., it helps to identify areas that may need to be addressed with other appropriate action(s) to mitigate potential safety concerns, such as by ensuring that the track over which the equipment is operating is maintained to standards appropriate for the specific equipment type, or by placing operational restrictions on the equipment, or both.

In addition to these comparisons, an overview of the new FRA qualification procedures which are used for demonstrating vehicle trackworthiness is provided in this paper. These procedures, which include use of simulations to demonstrate dynamic performance, are intended to give guidance to vehicle designers and provide a more comprehensive tool for safety assessment and verification of the suitability of a particular equipment design for the track conditions found in the U.S.