I ran the railroad retirement accounting at three railroads. I am vested with 127 months. El Coke will have to wait a year longer than I to see if the fund survives. At two companies I was asked to do an analysis of the choice: would an employee be better off under RRB or SS with using the extra funds invested in an IRA. The results were the same both times. The extra funds that railroads and their employees put into the fund do not earn a rate of return even matching a good mix of investments or certificates of deposit. It is a good program for what it is, but it is not a great way of investing money for retirement.
I personnally have done significantly better, even in poor stock markets taking the difference between RRB and SS and investing these funds in an IRA.