Sorry to say, but this 55 KMPH rule of IR is just idiotic. There shouldn't be any specific rule to it. This mps should vary from route-to-route. Ex. HWH-DHN or NDLS-CNB stretch can never be compared with GHY-DMV stretch. Infact, a train which has greater speed and lesser stops than others enroute should be called an SF for that specific route. In HWH-DHN stretch where most of the trains are doing 70-80 comfortably, then 55 should not be a measurement here for an SF. Had it been in RNC-DHN section, then it might be considered...