"Adam H. Kerman"  .   
   >   
   > This came up in a Yahoo group. As one would expect without CTC, IC had   
   > no convenient method of reversing the flow of traffic on a main. So how   
   > was it done? How were trains given permission to pass trains on the other   
   > main, and how were trains in the other direction held? Was the train being   
   > passed the one given permission to throw switches and hold on the other   
   > main? Were these done as a series of orders in a train order given over   
   > the radio? Or were these movements scheduled?   
      
   I don't know the answers exactly, but I know how directional double track   
   works on GCOR railroads today and can interpolate the rest.   
      
   Movement authorities these days are issued by radio in the form of track   
   warrants authorizing movements from point A to point B, usually in a single   
   direction only. The dispatcher can give overlapping authorities only if   
   there is some supplemental form of protection in place. In the case of   
   double track, there is usually a signal system that protects trains moving   
   with the current of traffic from experiencing nose-to-tail collisions, so   
   the dispatcher can issue warrants for multiple trains to move over the same   
   piece of track so long as they're moving with the current. On the other   
   hand, the signal system provides no protection against head-on collisions,   
   and no protection against rear-end collisions for trains moving against the   
   current of traffic, so if a train has a warrant for movement in the "wrong"   
   direction, no other train can get a warrant on that piece of track.   
      
   In timetable / train order days it basically worked the same way. Scheduled   
   trains got their authority from the timetable, modified by orders; extras   
   got theirs from orders. Again the dispatcher could only authorize   
   conflicting movements if there was an alternative form of protection in   
   place. By default, trains moving against the current of traffic had to   
   protect their movement with a flagman, but their orders could relieve them   
   of this obligation (if the dispatcher had issued orders to other trains to   
   ensure that no conflicting movements were authorized).   
      
   Hand-throw switches on the main line work similarly: per rule, a train must   
   return every switch to its "normal" position when it is past it, but the   
   dispatcher can relieve them of that obligation if he informs the next train   
   through that the switch is not in normal position. (Normal position usually   
   means lined for the straight route, unless specified otherwise in the   
   timetable; a switch that is not in normal position is "open" or "reverse".)   
      
   When trains had cabooses, the default rule worked quite well because there   
   were guys at the back of the train to restore each switch once the train   
   was past. Sure, the train using the switch had to stop twice (once for the   
   head brakeman to open the switch and once for the rear brakeman to restore   
   it to normal), but they were short stops. But now, the conductor gets off,   
   opens the switch, and has to stay there until the train is past, so that he   
   can restore the switch. When he's done that, he has to walk up to the head   
   end or catch a ride from a crew van if available.   
      
   So more often than not, trains are permitted to leave the switch in the   
   reverse position, and the next train through has to stop and restore it   
   (unless it is also using the diverging route).   
      
   If a passenger train needs to overtake a freight, you either have to make   
   the passenger train cross over to the wrong track and back - stopping twice   
   to throw switches, and leaving both crossovers open behind them so that   
   other trains will also have to stop - or you have to cross the freight   
   train over to the wrong track and find a way to get the freight conductor   
   back into the locomotive.   
      
   Power switches solve a lot of problems, and in cases where train counts are   
   low enough to be handled with single track and sidings, CTC single track   
   may well be better than double track with directional signaling and   
   hand-throw crossovers. You can also have directional double track with   
   power switches at the crossovers (usually with an "island" of CTC at each   
   set of crossovers), which is almost always going to give smoother train   
   operation, and if you then fill in the space between crossovers with   
   bidirectional CTC signaling, you get the best of all worlds but at the   
   highest cost.   
      
   Dan   
      
   --- SoupGate/W32 v1.03   
    * Origin: LiveWire BBS -=*=- UseNet FTN Gateway (1:2320/1)