Per AAR Field Manual Rule 90, cars built after July 1, 1974 are 50 year tank cars. Per 49 CFR § 215.203, these cars are prohibited from being in transportation after it has exceeded its 50 year life to the month it was constructed. Unless a freight car has been approved for increased life status by the FRA and the AAR, it must be to its final destination by the end of that month.