Continuous welded rail is laid down from 1/4 mile sections carried on special rail cars. These photos taken February 5, 2008 at Sandy Hook Yard in Lynchburg, VA
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Rail cars carrying the continuous welded rail
On the lookout platform midway on the train
   
This machine welds the sections along the way
 
 
The rail is cut near crossings. Notice the shower of sparks from the cutting torch near the bottom of the photo