From: stephen@sprunk.org   
      
   On 05-Oct-14 14:24, Overmod (Robert M. Ellsworth) wrote:   
   > Top-down track is aligned using the contact area of the railheads as   
   > the alignment data, rather than working from the bed upward.  It's   
   > pretty common design practice for Class 9 track construction.  Here   
   > is a reference (downloadable .pdf, FRA Research Report RR-08-03 from   
   > July 2008) that references top-down construction with respect to slab   
   > track:   
   >   
   > ntl.bts.gov/lib/42000/42800/42879/rr0803.pdf   
      
   Thanks; looks like good reading.   
      
   S   
      
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