From: stephen@sprunk.org   
      
   On 10-Apr-15 08:54, Clark F Morris wrote:   
   > hancock4@bbs.cpcn.com wrote:   
   >> On a section of busy bi-directional double track that CSX shares   
   >> with SEPTA, CSX is spending money to build a third track dedicated   
   >> for its trains.  I think this is foolish.  CSX will go from a very   
   >> fluid two-track line to a single track line that will hurt, not   
   >> help its freight trains.  The two-track line was busy, but not   
   >> over-crowded, and the bi-directional signalling made it flexible.   
   >   
   > Given that SEPTA needs to upgrade to high level platforms for ADA   
   > and performance reasons, this could make a lot of sense.   
      
   For the high platform issue, gauntlet tracks are cheaper and take up a   
   lot less space than building a separate track, and the performance of   
   freights will be a lot better if they can still use two tracks, rather   
   than have to use a single track bidirectionally.   
      
   > Differing speed bands and maintenance needs (50 mph heavy haul   
   > versus 80 - 90 mph every 15 minute or half hourly passenger service)   
   > can make separate lines the best answer.   
      
   No, you just need to learn how to use fixed slots.  Those "faster"   
   commuter trains probably average about the same speed once you factor in   
   all the stops they make--especially on SEPTA, which has closer stops   
   than most other "commuter" systems.   
      
   Intercity trains they have a much higher average speed, but you _can_   
   create slots that move at different speeds; the math is a bit more   
   difficult, but it's still cheaper than additional tracks.   
      
   > Switches are expensive.   
      
   Not as expensive as adding an entirely new track, especially once you   
   figure in having to widen every bridge and crossing on the route.   
      
   That's why many trunk lines are still mostly single tracked, even though   
   that requires frequent sidings (with two switches each) for passing.   
      
   S   
      
   --   
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   CCIE #3723         "God is an inveterate gambler, and He throws the   
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