From: r.m.ellsworth@att.net   
      
   >> What does "top-down track system" mean?   
      
   > In direct fixation, it means top of rail and gauge are established to the   
   > specification, then the fasteners are attached, then the concrete is placed   
   > last. That really makes a lot of sense, because there's just the one step   
   > at which things are calibrated. Bottom up requires a lot more calibration.   
      
   In connection with direct fixation, you might enjoy some of the references on   
   the GERB company's Web site:   
      
   http://www.gerb.com/en/arbeitsgebiete/arbeitsgebiete.php?ID=107&kategorie=5   
      
   Note the 'sidebar' at top right with some technical descriptions of the   
   instantiations.  This is more than just direct fixation, but I think it is   
   significant if the track is to be used for effective high speed.   
      
   (The Germans have a long and fascinating history with sprung track...)   
      
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