Following quickly on the heels of a National Transportation Safety Board warning about the D.C. Metro’s crash-prevention system, U.S. DOT regulators are asking transit agencies nationwide to ensure they have safety backups in place.

As Peter Rogoff, chief of the Federal Transit Administration (FTA), wrote to officials [PDF] late yesterday:

We are asking that all train operators that have train control systems capable of monitoring train movements determine whether their systems have adequate safety redundancy if losses in train detection occur.

If a system is susceptible to a single-point failure, we urge you to take corrective action immediately to add redundancy by evaluating track occupancy on a real-time basis …

The House oversight committee’s D.C. panel is holding a hearing this afternoon on the June 22 D.C. Metro crash that left nine dead, including the train operator.