Railway Track & Structures - October 2007 - (Page 38)

Risk management Table 1, left: Broken-rail risk guidelnes. Figure 2, above: Derailment rate vs. service defect rates, U.S. Class 1 railroads, 1995-2003. injuries and fatalities can occur for this type of derailment such as was the case with the Hatfield derailment in the United Kingdom, where four people were killed and 30 injured as a direct result of a broken-rail derailment. Research studies have shown a relationship between rail defect occurrence, particularly service defects that are located by means other than rail testing, and broken-rail derailments. Recent studies indicate that a broken-rail derailment occurs approximately every 133 service defects for a derailment per service defect rate of 0.0075. Increased testing can reduce this risk, with both the service defect rate and the number of derailments decreasing with increased testing. However, increased testing is expensive and, as such, must be optimized. Simply increasing testing across the board is not the best approach. Rather, targeted increased inspection, focusing on “high-risk” locations, offers a more cost-effective alternative. Quantification of this broken-rail risk can be used to fine tune rail testing. This has been shown to have the effect of reducing service defect rates and associated broken-railcaused derailments. This technique was originally developed by Volpe National Transportation Systems Center in the early 1990s and subsequently modified and implemented by railroads and consultants such as ZETA-TECH’s RailTest ultrasonic test scheduling model, which has been applied extensively in the United States and Europe. The objective of this analysis methodology is to schedule ultrasonic testing so that a defined level of risk of rail failure is held constant, even as rail ages. Risk is defined as the number of service defects (e.g., rail breaks) per mile per year, which, as noted above, is related to the occurrence of broken-rail derailments. Table 1 presents risk guidelines developed through application of this broken-rail-risk methodology on a broad range of freight and passenger railways in North America and Europe. High-risk track segments are thus identified and are candidates for improved UT test scheduling, which has been shown to reduce rail service defects and corresponding rail-related derailments. Figure 2 shows a reduction in service-defect and derailment rate for a major U.S. Class 1 railroad with application of riskbased test scheduling. Track geometry Track geometry represents another major area of trackcaused derailments with more than 400 derailments a year reported. Track-geometry-related derailments refer to those derailments where the geometry of the track is at or near FRA safety limits or where the interaction between the vehicle and track can lead to unsafe vehicle dynamic response and subsequent derailment. Two risk management tools address this area. The first is 38 Railway Track & Structures October 2007 www.rtands.com http://www.rtands.com

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Railway Track & Structures - October 2007 Contents On Track Industry Today Supplier News AREMA News NRC News TTCI R&D Crossties by the Billions Provide Essentials for Full Support Modern Tools Manage Risk M/W Challenges: Better Management of Thermal Forces in CWR TTCI Celebrates 25 Years as Facility, 10 as Part of AAR Products and Literature People Calendar Sales Representatives Website Directory Advertisers Index Professional Directory Classified Advertising Chicago Perspective

Railway Track & Structures - October 2007

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