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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