49 C.F.R. § 299.411
(a) Wheel climb.
(1) Suspension systems shall be designed to reasonably prevent wheel climb, wheel unloading, rail rollover, rail shift, and a vehicle from overturning to ensure safe, stable performance and ride quality. These requirements shall be met—
(2) All passenger equipment shall meet the safety performance standards for suspension systems contained in § 299.609(h). In particular—