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Friction Coefficient 0.6
1.2
3rd Axle (IRW) High Rail Wheel L/V
1
0.8
0.6
0.4
NADAL Limit 7.5 inch CD, no pert
0.2 7.5 inch CD, pert1 4.0 inch CD, pert2
15 mph, pert3 4.0 inch CD, pert1
0
100 500 900 1300 1700 2100 2500 2900
Curve Radius (feet)
Figure 39. Wheel L/V ratio, Type 2 light rail vehicle, friction
coefficient 0.6.
curves with radii greater than or equal to 955 ft at a 4.0 in. cant curving L/V ratio exceeded the Nadal value or the vehicle
deficiency speed under Level 2 perturbations. The derailment derailed with a 0.6 W/R friction coefficient. Curves with radii
was caused by resonance responses of the Type 2 vehicle at less than those shown in the following tables are recommended
higher speeds. The Type 2 light rail vehicle with a 75° flange for guard rail installation. Table 8 lists the simulation results
angle wheel can run safely at a 4.0 in. cant deficiency speed on with a 0.55 friction coefficient for the less conservative guard
curves with radii larger than 100 ft and Level 1 perturbations. rail installation application.
Tables 9 and 10 list the dynamic curving simulation results
on main-line curves with a 0.6 W/R friction coefficient and at
4.4 Summary of Flange Climb
speeds of 4.0 and 7.5 in. cant deficiency, respectively.
Derailment Simulations
The following conclusions can be drawn from the flange
Dynamic curving simulations of the four types of transit climb derailment simulations of Type 1 and 2 transit rail cars
rail cars and light rail vehicles with three different flange angle and light rail vehicles with various flange angle wheels:
wheels (IRW for Type 2 light rail vehicles only) at 15 mph on
yard track were conducted using the NUCARS program. · There are many factors leading to flange climb derailment,
Table 7 lists the radii of the curves where either the dynamic but three of them have the most critical effects: wheel flange
Table 7. Flange climb derailment on yard curves with a W/R friction coefficient of 0.6 at 15 mph.
Perturbation Transit Rail Car Type 1 Transit Rail Car Type 2 Light Rail VehicleType 1 Light Rail Vehicle Type 2
Level 63 70 75 63 70 75 63 70 75 63 70 75
1 R<=500* LTN** LTN R<=955 LTN LTN R<=500 R<=320 LTN R<=1,145 LTN LTN
2 R<=755 R<=320 LTN R<=2,000 R<=320 LTN R<=1,145 R<=955 R<=500 R<=3,000 R<=500 LTN
3 R<=3,000 R<=320 LTN R<=3,000 R<=320 LTN R<=3,000 R<=1,145 R<=755 R<=3,000 R<=3,000 LTN
Note: *R<=320 indicates that the 3-ft window L/V ratios on curves with radii lower or equal to 320 ft exceeded Nadal values or the vehicle derailed.
**LTN indicates that the L/V ratios of all simulated cases with curve radii from 100 to 3000 ft are less than Nadal values, and derailment is not expected.
Table 8. Flange climb derailment on yard curves with a W/R friction coefficient if 0.55 at 15 mph.
Light Rail Vehicle Type
Perturbation Transit Rail Car Type 1 Transit Rail Car Type 2 Light Rail Vehicle Type 1 2
Level 63 70 75 63 70 75 63 70 75 63 70 75
1 R<=320 LTN LTN R<=500 LTN LTN R<=320 LTN LTN R<=320 LTN LTN
2 R<=500 LTN LTN R<=1,145 LTN LTN R<=955 R<=500 LTN R<=3,000 LTN LTN
3 R<=1,145 LTN LTN R<=1,145 LTN LTN R<=2,000 R<=755 LTN R<=3,000 LTN LTN

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Table 9. Flange climb derailment on main-line curves with a W/R friction coefficient
of 0.6 at 4-in. cant deficiency.
Light Rail Vehicle Light Rail Vehicle
Perturbation Transit Rail Car Type 1 Transit Rail Car Type 2 Type 1 Type 2
Level 63 70 75 63 70 75 70 75 70 75
R>=1,145, R>=1,145,
1 R<=500 LTN LTN R<=755 LTN LTN <=2,000* LTN <=2,000 LTN
R<=320,
2 R=955
R<=755,
3 R=2,000 R>=2,000 R=500
Note: *R>=1,145,<=2,000 indicates that the 5-ft window L/V ratios on curves with radii greater than or equal to 1145 ft, but less than or equal to
2,000 ft exceeded Nadal values or the vehicle derailed.
Table 10. Flange climb derailment in main-line curves with a W/R friction coefficient
of 0.6 at 7.5-in. cant deficiency.
Light Rail Vehicle Light Rail Vehicle
Perturbation Transit Rail Car Type 1 Transit Rail Car Type 2 Type 1 Type 2
Level 63 70 75 63 70 75 70 75 70 75
R>=755,
1 R<=500 LTN LTN R<=500 LTN LTN R<=320 LTN <=2,000 R=2,000
R<=320, R<=755, R<=500,
2 R=2,000 LTN R=2,000 =3,000 R<=3,000 R<=3,000
3 R=955 R=755 R>=1,145 R<=3,000 R<=3,000 R<=3,000 R<=3,000
angle, W/R friction coefficient, and track perturbation Guard rails should be installed on curves with radii less
amplitude. than or equal to 755 ft for the Type 1 light rail vehicle.
· Flange climb derailment risk decreases as the wheel flange For main-line curves, these are the following guard rail
angle increases: the larger the wheel flange angle, the smaller installation guidelines:
the guarded curve radius. No guard rails are needed for Type 1 and 2 transit rail
· Flange climb derailment risk decreases as the W/R friction cars running at a 7.5 in. cant deficiency speed with
coefficient decreases: the lower the friction coefficient, the Level 2 (Figure 20) track perturbations.
smaller the guarded curve radius. No guard rail is needed No guard rails are needed for Type 1 light rail vehicles
for all simulated vehicles if the friction coefficient can be running at a 7.5 in. cant deficiency speed with Level 1
controlled under 0.4. (Figure 19) track perturbations.
· Flange climb derailment risk increases as track perturbation No guard rails are needed for Type 2 light rail vehicles
increases; the smaller the track perturbation amplitude, the running at a 4.0 in. cant deficiency speed with Level 1
smaller the guarded curve radius. track perturbations.
· TTCI recommends to adopt 75° flange angle wheels for Guard rails should be installed on curves with radii
both transit rail cars (Type 1 and 2) and light rail vehicles less than or equal to 500 ft for Type 1 light rail vehicles
(Type 1 and 2) to prevent flange climb derailment. running at a 4 in. cant deficiency speed with Level 2
· From a safety point of view, the guard rail installation track perturbations.
guidelines for the simulated two types of transit rail cars Guard rails should be installed on curves with radii
and two types of light rail vehicles (defined in Table 2 in greater than or equal to 955 ft for Type 2 light rail
the report) with recommended 75° flange angle wheels are vehicles running at a 4 in. cant deficiency speed with
listed below: Level 2 track perturbations.
For yard curves (15 mph speed limit) with the most · Vehicle curving performance is different from case-to-case
severe (Level 3, shown in Figure 21 in the report) track due to many factors from vehicle and track aspects. The above
perturbations, these are the following guard rail instal- guidelines and details in Tables 7 through 10 of the report
lation guidelines: could be used as a reference and applied by taking into
No guard rails are needed for Type 1 and Type 2 account the specific vehicle/track features and running
transit rail cars or Type 2 light rail vehicles. environment.