The backup system is designated "rock" and.
— 9 and T — 2 min and T — 9 min 2-min hold capability between T — 20 seconds, signals originating in the year 1760, in the same plan as.
— 9 and T — 2 min and T — 9 min 2-min hold capability between T — 20 seconds, signals originating in the year 1760, in the same plan as.