20 C.F.R. § 234.40
The residual lump-sum (RLS) is the means by which railroad employees and their survivors are guaranteed to receive at least as much in benefits as the employee paid in railroad retirement taxes during the years 1937 through 1974. An RLS payment can be made only if it appears that no other benefits based at least in part on railroad service will be payable under either the Railroad Retirement Act or Social Security Act in the future. The residual is reduced for any retirement benefits that were paid on the basis of the employee's railroad service, and for any survivor benefits based on the employee's earnings already paid by either the Board or the Social Security Administration. A widow(er) or dependent parent can, before attaining age 60, elect to waive future rights to monthly benefits based on the employee's railroad service in order to receive the RLS.
20 C.F.R. § 234.40