Interface - The Journal of Wheel/Rail Interaction

WAYSIDE LOAD DETECTION

Using Wayside Load Detectors for Preventive Vehicle Maintenance
(Part 1 of 2)
By B. McGuire, R. Sarunac, R. B. Wiley and P. Klauser • April, 2007

The use of vehicle performance detectors is steadily growing on North American freight and high-speed passenger railways. With the installation of a Wayside Wheel/Rail Load Detector (WRLD) on the Washington Metropolitan Area Transit Authority (WMATA), the trend now extends to the rail transit industry, as well.

The original truck performance detector (TPD) was developed in the mid-1990s by the Transportation Technology Center, Inc., through the Association of American Railroads' (AAR) research program. TPDs measure wheel/rail forces via strain gauge sensors on the rails in selected reverse curves. They also can measure the angle of attack of each axle with respect to the rail — a parameter that, in combination with measured vertical and lateral forces, provides information regarding the steering capability of a truck through curves.

TPDs identify suspension systems that do not perform optimally in (or after negotiating) curves. Poor performance may result in derailments due to wheel climb, gauge spreading, rail rollover or track panel shift. Poor performance also contributes to wear on rail, special trackwork, wheel profiles and flanges. By identifying poor performers through performance-based monitoring, preventive maintenance can be performed, reducing derailment risks and improving the overall safety of rail operations.

TPDs are designed to measure rail vehicle curving performance under specific conditions. Measurements (shown in Figure 1) include:

— Vertical Force. The force generated by the wheel perpendicular to the plane of the track.

— Lateral Force. The force generated by the wheel in the plane of the track but perpendicular to the direction of motion.

— Angle of Attack. The angle taken by the axle relative to the direction of motion.

A typical TPD site consists of an “S” curve arrangement where two curves (typically 4 to 6 degrees) are in the opposite direction relative to each other (i.e., a right-hand and a left-hand curve with a tangent section separating them). A modified form of a TPD in the form of a single-curve load station, a Wayside Wheel/Rail Load Detector (WRLD), was installed at WMATA.

Originally, wayside detectors (such as hotbox, wheel impact load and TPDs) were intended for use in exception reporting. Whenever an axle roller bearing temperature, wheel impact or truck performance indicator exceeds a pre-determined threshold, an alarm is raised and the offending item is removed from service at the earliest opportunity. This is the simplest use of wayside detectors.

Within the past few years, TPD data has been used to monitor changes in repeated performance over time and to predict when an alarm condition will be reached. Additionally, the performance profile of a suspected “bad actor” can be compared to peer vehicles or an expected normal performance profile. This allows for prioritization of maintenance plans for the equipment most in need of repair. It also provides a means to declare a vehicle as consistently performing within normal and safe operating ranges for various performance indices, and, thus, not in need of maintenance. In order to accommodate this new approach to performance monitoring, a system, known as InteRRIS®, was designed to process, store, analyze and automatically report on vehicle condition (see Figure 2 next page).

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