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OCR for page 24
24 CHAPTER 5 Conclusions This report compared two guard rail installation philoso- · Flange climb derailment risk increases as track perturba- phies and the effects of vehicle types, wheel flange angle, W/R tion increases; the smaller the track perturbation ampli- friction coefficient, curve radius, cant deficiency, and track tude is, the smaller the guarded curve radius will be. perturbation on flange climb derailments through NUCARS · TTCI recommends the adoption of 75° flange angle wheels simulations. As a result, a number of conclusions and recom- for both transit rail cars (Type 1 and 2) and light rail vehicles mended guidelines were drawn for guard/restraining rail (Type 1 and 2) to prevent flange climb derailment. installation in terms of vehicle type and track geometry, · From a safety point of view, the guard rail installation guide- including the following: lines for the simulated Type 1 and Type 2 transit rail cars and the Type 1 and Type 2 light rail vehicles (defined in Table 2 · Philosophy I (shared contact between the high-rail flange in the report) with recommended 75° flange angle wheels and the guard rail on the low-rail wheel) leads to better are listed below: vehicle dynamic performance than Philosophy II (no high- For yard curves (15 mph speed limit) with the most rail flange contact and with the guard rail contact on the severe (Level 3, shown in Figure 21) track perturba- low-rail wheel) in terms of lower lateral forces on rails, lower tions, the following guard rail installation guidelines are vehicle rolling resistance, and lower leading axle wear. recommended: · Both philosophies lead to higher vehicle rolling resistance No guard rails are needed for Type 1 and Type 2 and leading axle wheel wear compared with the case with transit rail cars or Type 2 light rail vehicles. no guard rail. Guard rails should be installed on curves with radii · The axle steering capability difference between these two less than or equal to 755 ft for the Type 1 light rail philosophies is negligible. vehicle. · The Nadal limit and flange climb distance limit are the For main-line curves, the following guard rail installation criteria for flange climb derailment; they are adopted as the guidelines are recommended: guard rail installation criteria in this report. No guard rails are needed for Type 1 and 2 transit rail · There are many factors leading to flange climb derailment. cars running at a 7.5 in. cant deficiency speed with Three factors that have the most critical effects are the wheel Level 2 (Figure 20) track perturbations. flange angle, the W/R friction coefficient, and the track per- No guard rails are needed for Type 1 light rail vehicles turbation amplitude. running at a 7.5 in. cant deficiency speed with Level 1 · Flange climb derailment risk decreases as wheel flange (Figure 19) track perturbations. angle increases: the larger the wheel flange angle, the smaller No guard rails are needed for Type 2 light rail vehicles the guarded curve radius. running at a 4.0 in. cant deficiency speed with Level 1 · The flange climb derailment risk decreases as the W/R track perturbations. friction coefficient decreases; the lower the friction coeffi- Guard rails should be installed on curves with radii less cient is, the smaller the guarded curve radius will be. No than or equal to 500 ft for Type 1 light rail vehicles guard rail is needed for all simulated vehicles if the friction running at a 4 in. cant deficiency speed with Level 2 coefficient can be controlled under 0.4. track perturbations.
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25 Guard rails should be installed on curves with radii report could be used as a reference and applied by taking greater than or equal to 955 ft for Type 2 light rail into account the specific vehicle/track features and running vehicles running at a 4 in. cant deficiency speed with environment. Level 2 track perturbations. · These guard rail installation guidelines do not apply to · Vehicle curving performance is different from case-to-case special trackwork, such as the guard rail for switches, due to many factors from vehicle and track aspects. The crossings, and turnouts. above guidelines and details in Tables 7 through 10 of the