Radio Blocking
The old way of train orders carried 2 ways of protecting a preceding train. First would be a scheduled, or TT train. His authority to operate on the main came from the TT, and his protection on both ends was covered under those specific rules. An extra train has several methods of protection. First one, is a signal system in conjunction with 19's. You are protected against following trains by at least 2 block signals (still in effect, today). If you are running dark, you couldn't put one train, on top of another. You ran, from station to station, with an operator reporting you clear of a block, or a qualified employee positively reporting an intact train, displaying markers, past a point of order. This is still a protection we enjoy (?) today, although things have gotten very lax, regarding what is required, to "believe" your train is still intact, and clear of a certain point. Even in the era of cabs and signals, the signal behind you didn't necessarily absolve you from protecting against a following train. You might have to anticipate another train running at restricted, or reduced speed, but you were still responsible for that hind end. Same for running half track speed, etc., but you addressed this, in your comment about flagging rules. There were always emergency provisions, for rescuing trains, track work, etc., but like today, everyone needed new paper, with the info to "remain at" for dead trains, and "assist and travel at restricted/reduced speed" for that assisting train, approaching from either direction. The basic jist of it all, although the terminology has changed, and the physical plant is different, both trackside and on the rails, the rules are still the same. In some cases, we have lost certain "protections" afforded us, in other areas, we have gained. We still have head-on and rear-end collisions, same as since the first trains shared a single track, so you can see, the system is far from perfect. (ATS would end collisions at a near 100% rate) I still don't like dark territory, and I have ZERO trust, or faith, in the guy on that other train. (if he is even only half as tired, and exhausted as me, it's too much). CTC, ABS and ATS are the only way to really, safely go. Regards, Brother Rob.....