A comprehensive review of technologies and approaches for active safety systems designed to reduce ground vehicle crashes, as well as the associated severity of injuries and fatalities, is provided. Active safety systems are commonly referred to as systems that can forewarn a driver of a potential safety hazard, or automatically intervene to reduce the likelihood of an accident without requiring driver intervention. The data from naturalistic drivers has shown that such systems are instrumental in improving vehicle safety in various conditions, particularly at higher speeds and under adverse road conditions. The increased integration of sensors, electronics, and real-time processing capabilities has served as one of the critical enabling elements in the widespread integration of active safety systems in modern vehicles. The emphasis is placed on control approaches for active safety systems and their progression over the years from antilock brakes to more advanced technologies that have nearly enabled semiautonomous driving. A review of key active safety control approaches for antilock braking, yaw stability, traction control, roll stability, and various collision avoidance systems is provided.

A detailed description of the Virginia Tech-Federal Railroad Administration (VT-FRA) Roller Rig measurement capabilities, along with the efforts in establishing the accuracy, repeatability, and integrity of the results are presented. The results of a series of baseline tests are also documented in an effort to provide an indication of the type of experiments that can be achieved on the rig. The one-fourth scaled rig is intended to be used for evaluating wheel-rail contact mechanics and dynamics with a high degree of precision. The rail is represented by a roller with a diameter that is five times larger than the wheel, in order to maintain the contact ellipse distortion to less than 10 percent. The primary point of differentiation between this rig and others that have been used in the past or are presently in use is that it is able to measure the wheel-rail contact forces with far greater precision than achieved in the past. The rig is also designed such that it provides a high degree of repeatability in testing, often needed for performing design of experiments accurately. The VT-FRA rig is capable of precisely controlling the lateral positioning of the wheel and rail, rail cant angle, the wheel-rail angle of attack, and the speed of the roller and wheel independently. The latter is intended to provide precise control of the relative speed of the wheel and roller, which amounts to precisely controlling creepage. Beyond presenting the rig’s capabilities, the paper provides a discussion of the initial results from the commissioning of the rig. It is concluded that the rig is ready to be commissioned for studies that are of interest to the practitioners in the rail industry and scientists in the research community.

In this study, the effect of natural third body layers on the coefficient of friction and contact forces is evaluated using the Virginia Tech-Federal Railroad Administration (VT-FRA) roller rig facility. The test rig allows us to precisely control the contacting surfaces to study its effect on the wheel-rail interface forces and moments. Experiments have shown while running the tests, a slight amount of wear occurs at the running surfaces. The worn material deposits at the surface and behaves like a “natural” third-body layer at the contact, resulting in changes in traction coefficient and creep forces. The material wear and its accumulation on the running surfaces change with wheel longitudinal load and creepage. A series of organized time-based experiments have been conducted with the running surfaces cleaned at the beginning of the test to study the effect of material wear accumulation on selected parameters including traction coefficient and creep forces over time. In order to highlight the effect of the natural third body layer on the wheel-rail contact forces, a series of experiments were conducted, in which the wheel and roller surfaces were cleaned in one case and left uncleaned in another. The results of the experiments are quite revealing. They indicate that when the running surfaces are cleaned after each test, the maximum creep force (or adhesion) is far lower than when the running surfaces are not cleaned, i.e., the natural third-body layer is allowed to accumulate at the surfaces. The results indicate that the wear debris act as a friction enhancer rather than a friction reducer.

This study evaluates the wheel-rail contact patch geometry of the VT-FRA roller rig, designed and commissioned at the Virginia Tech’s Railway Technologies Laboratory (RTL). Contact patch measurements are crucial for better analyzing the underlying factors that affect the wheel-rail interface (WRI) contact mechanics and dynamics. One of the challenges is in determining the size and pressure distribution at the contact patch, under various conditions. Although past studies have attempted to reach a method that can be used to make such measurements, more research is needed in reaching a practical and consistent method. This is particularly true for making the measurements under dynamic conditions. The use of pressure sensitive films was considered as the means for contact patch measurements on the VT-FRA rig, however, the thickness of the film influences the contact patch area and shape. This paper provides the results of the measurements with films with different range of pressure sensitivities. Three types of pressure-sensitive films are used under static conditions. The films are placed in between the wheel and roller in exact positions to enable comparing the test results for various wheel loads. The contact patch measured by the most sensitive film, which reacts to pressures as low as 0.5 MPa, provides the most accurate outline for the contact patch, although it does not provide the highest resolution for the pressure distribution. The other pressure-sensitive films that are used have a higher pressure range, with minimums of 49.0 MPa and 127.6 MPa. The relationship between the size of the contact patch and average contact pressure is evaluated as a function of the wheel load. The results indicate that with increasing wheel load, the size of the contact patch changes minimally, with the average pressure increasing in a nearly linear relationship to the wheel load as expected.

This study presents an experimental study of the effect of Top-of-Rail Friction Modifiers (TORFM) in quantities ranging from a small to a large amount on the progression of wheel-rail wear, using the Virginia Tech-FRA (VT-FRA) roller rig. TORFM behaves as a third body layer in between the wheel and rail and is applied to reduce wheel and rail wear while preserving a stable traction condition. An added benefit of TORFM is that it is estimated that it can reduce fuel consumption by controlling friction, although we are not aware of any proven data in support of this. Although widely used by the U.S. Class I railroads, there exists no proven method for determining, qualitatively or quantitatively, how the amount of TORFM and rail/wheel wear are related. Simply put, would increasing TORFM amount by a factor of two reduce wheel/rail wear and damage by one-half? How would such doubling effect traction or the longevity of TORFM on the wheel/rail surface? In this study, the VT-FRA roller rig is used to perform a series of tests under highly controlled conditions to shed more light on answering these questions. A series of controlled experiments are designed and performed in order to investigate the potential factors that may influence the traction performance. The wheel surface profile is measured by a high-precision, 3D, laser profiler to measure the progression of wheel wear for the duration of the experiments. The results indicate that it takes as much longer time for the traction force (traction coefficient) to reach a condition that is the same as the unlubricated rail, when compared between lightly-, moderately-, and heavily-lubricated conditions. The results further indicate that wear generation is delayed significantly among all lubrication conditions — even, the lightly-lubricated — when compared with the unlubricated conditions. A further evaluation of the results and additional tests are needed to provide further insight into some of the preliminary results that we have observed thus far.