As market forces drive up the gross weight on rail, railroads continue moving toward increased usage of heavy axle load (HAL) equipment, namely 286,000 lb and 315,000 lb GWR vehicles that provide more competitive and efficient transportation. According to the AAR's Universal Machine Language Equipment Register (UMLER) database, since 1995, at least 70% of vehicles built each year were HAL vehicles. 2005 had 49,923 more HAL vehicles running on the North America railroad system than the previous year. This practice can result in significant overall savings in operating costs. However, HAL equipment can also accelerate wear and damage to the railroad infrastructure and have a greater potential for truck warping and vehicle dynamics problems. Thus, keeping rolling stock and track safe while ramping up the usage of HAL equipment presents a significant challenge. Wheel Impact Load Detector (WILD) SuperSites, developed by Salient Systems Inc. (SSI), provide real time monitoring and alarming on excessive axle loads and vehicle dynamics. SuperSites are important tools in the scientific study of HAL vehicles and the monitoring of heavy haul operations. This paper provides a snapshot of results of studies conducted on Union Pacific (UP) HAL routes and demonstrates how HAL loads affect the rolling stock, the track, and the wheel/rail interaction. The heavier the load, the higher the impact of the defective wheels to the track; therefore, heavily loaded vehicle routes (such as the coal route from the Powder River Basin to Kansas City and the primary intermodal route from Los Angeles to El Paso) need to be monitored more proactively to avoid track structural damage.

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