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