Track-Related Research, Volume 7: Guidelines for Guard/Restraining Rail Installation (2010)

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24 This report compared two guard rail installation philoso- phies and the effects of vehicle types, wheel flange angle, W/R friction coefficient, curve radius, cant deficiency, and track perturbation on flange climb derailments through NUCARS simulations. As a result, a number of conclusions and recom- mended guidelines were drawn for guard/restraining rail installation in terms of vehicle type and track geometry, including the following: • Philosophy I (shared contact between the high-rail flange and the guard rail on the low-rail wheel) leads to better vehicle dynamic performance than Philosophy II (no high- rail flange contact and with the guard rail contact on the low-rail wheel) in terms of lower lateral forces on rails, lower vehicle rolling resistance, and lower leading axle wear. • Both philosophies lead to higher vehicle rolling resistance and leading axle wheel wear compared with the case with no guard rail. • The axle steering capability difference between these two philosophies is negligible. • The Nadal limit and flange climb distance limit are the criteria for flange climb derailment; they are adopted as the guard rail installation criteria in this report. • There are many factors leading to flange climb derailment. Three factors that have the most critical effects are the wheel flange angle, the W/R friction coefficient, and the track per- turbation amplitude. • Flange climb derailment risk decreases as wheel flange angle increases: the larger the wheel flange angle, the smaller the guarded curve radius. • The flange climb derailment risk decreases as the W/R friction coefficient decreases; the lower the friction coeffi- cient is, the smaller the guarded curve radius will be. No guard rail is needed for all simulated vehicles if the friction coefficient can be controlled under 0.4. • Flange climb derailment risk increases as track perturba- tion increases; the smaller the track perturbation ampli- tude is, the smaller the guarded curve radius will be. • TTCI recommends the adoption of 75° flange angle wheels for both transit rail cars (Type 1 and 2) and light rail vehicles (Type 1 and 2) to prevent flange climb derailment. • From a safety point of view, the guard rail installation guide- 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 in the report) with recommended 75° flange angle wheels are listed below: – For yard curves (15 mph speed limit) with the most severe (Level 3, shown in Figure 21) track perturba- tions, the following guard rail installation guidelines are recommended:  No guard rails are needed for Type 1 and Type 2 transit rail cars or Type 2 light rail vehicles.  Guard rails should be installed on curves with radii less than or equal to 755 ft for the Type 1 light rail vehicle. – For main-line curves, the following guard rail installation guidelines are recommended:  No guard rails are needed for Type 1 and 2 transit rail cars running at a 7.5 in. cant deficiency speed with Level 2 (Figure 20) track perturbations.  No guard rails are needed for Type 1 light rail vehicles running at a 7.5 in. cant deficiency speed with Level 1 (Figure 19) track perturbations.  No guard rails are needed for Type 2 light rail vehicles running at a 4.0 in. cant deficiency speed with Level 1 track perturbations.  Guard rails should be installed on curves with radii less than or equal to 500 ft for Type 1 light rail vehicles running at a 4 in. cant deficiency speed with Level 2 track perturbations. C H A P T E R 5 Conclusions

25  Guard rails should be installed on curves with radii greater than or equal to 955 ft for Type 2 light rail vehicles running at a 4 in. cant deficiency speed with Level 2 track perturbations. • Vehicle curving performance is different from case-to-case due to many factors from vehicle and track aspects. The above guidelines and details in Tables 7 through 10 of the report could be used as a reference and applied by taking into account the specific vehicle/track features and running environment. • These guard rail installation guidelines do not apply to special trackwork, such as the guard rail for switches, crossings, and turnouts.