Interface - The Journal of Wheel/Rail Interaction

W/R INTERACTION ON TRANSIT SYSTEMS

Managing Wheel/Rail Interaction on Rail Transit Systems
By Bob Tuzik • January, 2008

All railways must deal with operating/engineering and vehicle/track interaction issues. But rail transit systems, which operate under the microscope of the urban environment, face special, often unique, challenges. Speakers at Rail Transit ’07, Advanced Rail Management and Interface Journal’s third seminar devoted to wheel/rail interaction on rail transit systems, identified some of the issues that transit properties face and some of the ways they’ve found to deal with them.

The Southeastern Pennsylvania Transportation Authority (SEPTA) and its consultant Zeta-Tech Associates, Inc., for example, examined two low-speed, wheel-climb derailments on its Market Frankfort Line. While factors such as rail type and operating parameters differed, wheel surface roughness from newly trued wheels played a role in both derailments. A change in wheel profiles from SEPTA's M3 profile (which has a 1:38 conicity and small radius in the flange/throat area) to the M4 profile (which has a 1:20 conicity and large radius in the flange/throat area) also was a factor in the derailments.

Onsite investigations and NUCARS simulation indicated that in the first derailment, wear (caused by the new M4 wheel profile) on the gauge corner of the stock rail led to a mismatch with SEPTA's older M3 wheel profile. This significantly increased the lateral forces and led the wheels with the M3 profiles to "walk off."

The surface roughness of newly trued wheels with the M4 profile was a contributing factor in the second derailment. Worn switch points provided a ramp for the new wheel, which under high lateral forces and high surface roughness caused the wheels to climb.

Investigations also showed that wheels and rails on SEPTA wear into a compatible pattern over time. A drastic change in the wheel/rail interface, however, disrupts the compatibility and can result in derailments. Even at that, looking at wheel and rail profiles alone, is not enough, said Donald Holfeld, Zeta-Tech's general director of field engineering. "You must also consider factors such as wheel gauge and track gauge and how they work together to become compatible."

The Washington Metropolitan Area Transit Authority (WMATA) installed a wayside Wheel/Rail Load Detector (WRLD) in order to identify poorly performing vehicles and prevent wheel climb derailments.The WRLD, which was supplied by the Transportation Technology Center, Inc. (TTCI), indicates truck performance by measuring lateral and vertical loads, and angle of attack (and corresponding values such as speed, average car weight and total train weight). Working with its consultants, Booz Allen Hamilton and the TTCI, WMATA found the WRLD to be an effective early warning device that can identify potential “troublemakers.”

"The wayside monitoring system allows us to identify poor performers and select individual vehicles for inspection and unscheduled preventive maintenance," said WMATA Vehicle Engineer Mike Hiller. This is useful in evaluating the dynamic/curving performance of individual vehicles and the fleet, overall. Through use of the WRLD system, WMATA expects to increase truck life by 10% - 25%, and wheel life by 50%. More significantly, it expects the WRLD system to eliminate wheel-climb derailments.

Another type of Wayside Wheel Condition Monitoring (WCM) system, developed by Teknis Electronics, was implemented at RailCorp’s CityRail 1,300-mile mixed freight/passenger network in Sydney, New South Wales, Australia. While this type of technology is well established in the freight industry, the implementation of a WCM system on a suburban network identified unique problems and requirements associated with mixed traffic.

The Teknis WCM system uses a combination of dynamic (accelerometers) and static (strain gauges) measurements to detect wheel defects at line speeds. In this application, rolling stock engineers worked closely with repair facilities to manage maintenance requirements, determine the root cause of the defects and develop early intervention strategies. The process has yielded a reduction in the number of wheel defects by a factor of 30, said Keith Bladon, Teknis’ managing director.

This system can isolate and trend small defects, identify out-of-round wheels and analyze damage potential and the causes of re-emerging wheel defects. It can also be used to monitor, plan and schedule maintenance requirements. “We’ve seen that 95% of wheel defects start small,” Bladon said.

Some wheel defects on passenger railroads and rail transit systems are a result of seasonal adhesion issues, caused by leaves on the rail in the fall. Slip-slide events caused by poor wheel/rail adhesion during these periods generate wheel flats, which increase maintenance requirements and reduce equipment availability. Research has shown that wheel/rail friction levels affect the extent of the damage to each wheel during a low-adhesion wheel slide, said Graham Curtis of DeltaRail Products, a supplier of technology addressing low-adhesion conditions. Left untreated, wheel flats generate out-of-round wheels, which are difficult to detect.

While the problems relating to seasonal adhesion issues in the UK are similar to those in the U.S., approaches to dealing with them differ. Railways in the UK typically employ systems such as Wheel Slip/Slide Protection (WSP) systems and equipment such as the SmartSander system to control wheel slip and braking efforts. By equipping a fleet of 100 Electric Multiple Units with the SmartSander system, for example, one UK railway reduced station overruns by 70%, and delay minutes by 73%, Curtis said. The low-adhesion incident rate dropped from 0.3 incidents per train per year to 0.08 — a 73% decrease. Wheel truing requirements were reduced by 60%. The SmartSander equipment has been adapted for use in the U.S. and is currently undergoing service testing on Metro-North.

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